Faculty Profiles - UMEHARA, Noritsugu

Effect of Water on Wear of DLC Coatings in High Temperature and Pressurized Ethanol Reviewed

Tokoroyama, T; Horikawa, S; Mimata, J; Umehara, N; Murashima, M

TRIBOLOGY LETTERS Vol. 72 ( 4 ) 2024.12

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology Letters

The friction and wear characteristics of a-C:H:Si and a-C:H coatings in an ethanol environment at 120 °C and 10 MPa focusing on the effects of water and dissolved oxygen in ethanol were investigated. The friction tests were conducted using an autoclave chamber, with gases (oxygen or nitrogen) and ethanol–water mixtures (0 and 6 vol.%). The wear acceleration of a-C:H:Si took place when it slid in ethanol with 6 vol.% water and pressurized by oxygen, thus the specific wear rate was the highest, approximately 1.8 × 10−7 mm3/Nm. The reason of this wear acceleration was assumed the effect of hardness reduction due to oxidation of the a-C:H:Si, so the O/C ratio by AES and the hardness of topmost surface by AFM nano-scratch were investigated. As a result, the higher O/C ratio showed higher specific wear rate due to the hardness reduction from 13.3 to 6.0 GPa. These findings highlight the role of water and dissolved oxygen in accelerating wear of a-C:H:Si coatings. Graphical abstract: (Figure presented.)

DOI： 10.1007/s11249-024-01910-z

Corrosion and tribological properties of ta-C/ta-C: Ta coatings: Analysis of the influence of Ta-O/Ta-C ratio Reviewed

Proposal of a model for the influence of coating area on the electric field at the tip of electrocautery for suppressing tip charring and surgical smoke generation due to blood heating Reviewed

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 18 ( 6 ) page： AMDSM00210 2024.11

Li, LL; Tokoroyama, T; Zhang, RX; Umehara, N

Vol. 198 2024.10

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology International

Multilayer ta-C/ta-C: Ta coatings with varying total thicknesses (300, 600, and 1000 nm) and layer thickness ratios (1:0.5, 1:1, and 1:2) between the ta-C layer and ta-C: Ta layer were prepared. The study investigated the static corrosion resistance and tribological properties of the coatings in the NaCl solution. The static corrosion resistance positive correlation depended on the coating surface's Ta-O/Ta-C ratio. The lowest friction coefficient of 0.05 was obtained from the coating with a total thickness of 1000 nm due to the formation of the graphitized transfer film on the counterpart surface. A decreased sp2/sp3 ratio and the formation of tantalum oxide on the wear scar contributed to the lowest corrosion current, corrosive defect density, and wear rate.

DOI： 10.1016/j.triboint.2024.109916

The development of B/Cr co-doped DLC coating by FCVA deposition system and its tribological properties at 300 °C Reviewed International coauthorship International journal

Zhang, RX; Lee, WY; Umehara, N; Tokoroyama, T; Murashima, M; Takimoto, Y

SURFACE & COATINGS TECHNOLOGY Vol. 487 2024.7

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Surface and Coatings Technology

The diamond-like carbon (DLC) coating prepared using filtered cathodic arc deposition (FCVA) lost its promising wear resistance under high temperatures. Element-doped DLC coatings have been investigated to suppress carbon oxidation reaction and subsequently enhance the wear resistance in high-temperature environments. Previous research clarified the excellent tribological properties of boron-doped DLC (B-DLC) but identified challenge such as arc discharge extinguishment and coating declamation (under high-temperature friction test). In this study, the introduction of Argon gas (10 sccm) during the deposition process stabilized stable arc discharge, resulting in high hardness and deposition rate. Moreover, a chromium interlayer and varying concentration of Cr dopant (0.5 %, 1.0 %, 3.0 % at.) were added to B-DLC to develop a stable, co-doped DLC with low friction and high wear resistance. Raman spectroscopy and nano-indentation revealed an increase in the disordered carbon structure and reduction in hardness and Young's Modulus with Cr doping. Macroscopic ball-on-disk friction test, showed 1 % Cr-doped B-DLC (a-C:B:Cr1) coating exhibited super low friction (avg. coefficient 0.02) and a low specific wear rate (<5.0 × 10−6 mm3/Nm). Raman spectroscopy indicated that the transferred graphite-like tribo-film onto the surface of Si3N4 counterparts contributed to stable low friction. Additionally, XPS analysis on the DLC coatings' wear track suggested the rich B–B bond might contribute to its high wear resistance. This successful improvement on element-doped DLC prepared by FCVA provided valuable insights for further exploration of DLC coating applied to various working situations.

DOI： 10.1016/j.surfcoat.2024.130968

Evaluating Palm Oil Ester Base Oils as Eco-Friendly Alternatives in Lubricant Formulation Reviewed International coauthorship

Samihah Mustaffha, Darius El Pebrian, Mohd Muhyiddin Mustafa, Noritsugu Umehara, Nik Roselina Nik Roseley, Mohamad Ali Ahmad, Nor Azmmi Masripan

Jurnal Tribologi Vol. 43 page： 158 - 168 2024.6

Tribocatalytic Reaction Enabled by TiO2 Nanoparticle for MoDTC-Derived Tribofilm Formation at ta-C/Steel Contact Reviewed International coauthorship International journal

COATINGS Vol. 14 ( 6 ) 2024.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Coatings

Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses surface damage in a high-temperature operating environment; however, it causes a detrimental effect that hinders the formation of a competent tribofilm. In this study, we dispersed highly reactive TiO2 nanoparticles (TDONPs) in molybdenum dithiocarbamate (MoDTC)-containing lubricant for adhering triboproducts on the DLC surface. In addition, TDONPs contributed to the decomposition of triboproducts by promoting the decomposition of MoDTC through its catalytic role. Rutile TDONPs were more helpful in reducing friction than anatase TDONPs and improved the friction performance by up to ~100%.

DOI： 10.3390/coatings14060773

Super hardening of Fe-W alloy plating by phase transformation of amorphous to metal carbides-dispersed nanocrystalline alloys and application as promising alternative for hard chromium plating Reviewed International coauthorship

J.H. Park, J.I. Kim, Y. Shinohara, T. Hagio, N. Umehara, R. Ichino

SURFACE & COATINGS TECHNOLOGY Vol. 477 page： 130388 2024.5

Creation of anti-frost micro-plastic texture surfaces enhancing thermal conductivity by carbon black containing in polyvinyl chloride Reviewed

T. Tokoroyama, L. Zhang, W. Wu, M. Murashima, N.Umehara

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 18 ( 3 ) page： JAMDSM0032 2024.5

Effect of PAO-4 and MoDTC + ZnDTP oil additive lubricants on the tribological performance of novel tetrahedral amorphous carbon (ta-C) coatings Reviewed International coauthorship International journal

Mustafa M.M.B., Umehara N., Tokoroyama T., Murashima M., Utsumi Y., Moriguchi H., Shibata A.

TRIBOLOGY INTERNATIONAL Vol. 193 2024.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology International

This study was carried out to assess the effect of PAO-4 and mineral oil mixed with MoDTC and ZnDTP on the tribological performance of novel tetrahedral-amorphous-carbon (ta-C) coatings namely P:ta-C, and M:ta-C, were analysed using the Pin-on-Disk Tribo-tester with a fixed normal load, temperature, sliding distance and speed of 20 N, 80 °C, 250 m and 0.068 ms−1 for 60 min, respectively. The C:ta-C, P:ta-C, and M:ta-C showed excellent wear resistance when lubricated with MoDTC + ZnDTP. The formation of weak Zn-derived tribofilm on the P:ta-C coating contributed to the strong wear resistance and reduced friction coefficient. Moreover, the passive transfer of ferrous compounds from the SUJ2 disk induced the development of weak Zn-derived tribofilm on the P:ta-C and M:ta-C.

DOI： 10.1016/j.triboint.2024.109396

The 1 μm wear particles entrainment in situ observation via fluorescent staining silica particles by silane coupling with Rhodamine B Reviewed

T. Tokoroyama, M. Okashita, N. Fusetani, M. Murashima, N. Hashizume, R. Tsuboi, H. Shiomi, N. Umehara

FRONTIERS IN MECHANICAL ENGINEERING-SWITZERLAND Vol. 10 page： 1371948 2024.4

The Influence of Succinimide Dispersant on the Formation of Tribofilm in ATF Friction Reviewed

TOKOROYAMA Takayuki, TERAI Yusuke, UMEHARA Noritsugu, MURASHIMA Motoyuki, HONDA Akiyuki, ADACHI Tsuneo

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. advpub ( 0 ) 2024.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

To elucidate the mechanism for suppressing wear of high-speed bearing steel (SUJ2) used in automatic transmission fluid (ATF), friction and wear tests were conducted in lubricating oils containing different concentrations of succinimide dispersant. The wear volume of the SUJ2 disk in the base oil was approximately 1.4×10⁴mm³. However, with the addition of 0.75 wt.% of succinimide dispersant, the wear volume decreased to about 0.4×10⁴mm³, approximately one-third of the original amount. In Fluid A and Fluid A I₀.₇₅-I₂.₇₅, the reduction in wear volume was observed only in Fluid A I₀.₇₅. This was believed to be due to the presence of succinimide dispersant, which led to the formation of iron oxide within the wear scars, and on the surface, FeS and FeS₂formed as tribofilms. In the case of Fluid A I₀.₇₅, the film hardness was higher, contributing to improved wear resistance. The sole reason for the increased hardness of the tribofilm in Fluid A I₀.₇₅was hypothesized to be the repeated friction of the tribofilm within the surface, leading to the deposition of FeS and FeS₂. This, in turn, was presumed to enhance the density of the tribofilm.

DOI： 10.18914/tribologist.23-00021

Lubricity performance of hydrogen-free CVD growth of graphene on copper particles as an additive in paraffin base oil Reviewed International coauthorship International journal

Rahman, NL; Amiruddin, H; Abdollah, MFB; Umehara, N

PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART J-JOURNAL OF ENGINEERING TRIBOLOGY Vol. 238 ( 7 ) page： 869 - 879 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology

This study aims to examine the impact of carbon precursor materials, which are oil palm fiber (OPF) and waste polystyrene (PS), on friction and wear properties of paraffin base oil added with graphene-coated copper (Cu) additive. The graphene was synthesized on Cu particles via hydrogen-free chemical vapor deposition method. The graphene was characterized using Raman spectroscopy and transmission electron microscopy. The lubricity properties of 0.6 wt.% of synthesized graphene-coated Cu additive in paraffin base oil was analyzed based on its tribological behavior using a four-ball tribometer. From the quantitative and qualitative characterization analysis, graphene-coated Cu additive synthesized using 50 wt.% OPF carbon precursors has a good-quality graphene with minimal defects and a well-ordered lattice structure. From the tribological analysis, the paraffin base oil added with graphene-coated Cu additive synthesized using 50 wt.% OPF carbon precursor has the lowest coefficient of friction of 0.07 and wear rate of 1.6 × 10−5 mm3/min. Hence, it can be suggested that incorporating graphene-coated Cu particles, synthesized from a 50 wt.% OPF carbon precursor, into base oil shows great potential as an environmentally friendly additive, particularly in terms of enhancing lubrication performance.

DOI： 10.1177/13506501241236826

The ta-C Hardness Effect on Wear Properties Under MoDTC Contained Boundary Lubrication Reviewed International coauthorship International journal

Tokoroyama, T; Wang, S; Umehara, N; Murashima, M; Lee, WY

TRIBOLOGY LETTERS Vol. 72 ( 1 ) 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology Letters

The accelerated wear of hydrogenated amorphous carbon in the presence of molybdenum dithiocarbamate (MoDTC) lubrication is a significant challenge when considering its application in engine components. While it is presumed that the use of high-hardness tetrahedral amorphous carbon (ta-C) can effectively address wear issues, irrespective of chemical wear caused by Mo-degradable materials, we have yet to understand the impact of ta-C coating hardness on wear when combined with MoDTC. This uncertainty arises from the assumption that the quantity and structure of Mo-degradable material may be linked to contact pressure, implying that even with a highly hard ta-C coating, wear may vary with the applied load. In this study, we prepared ta-C coatings with four different hardness levels (such as approximately 18.2, 22.1, 46.6, and 53.6 GPa) and conducted friction tests to elucidate the influence of ta-C hardness on wear characteristics under boundary lubrication with MoDTC. Subsequently, we performed chemical analysis (Raman, EDS, and XPS) to identify the chemical species present in the tribofilm, with a particular focus on the 22.1 GPa ta-C coating as a representative of low-hardness ta-C coatings. Our findings revealed that wear suppression was achieved the contact pressure exceeded 200 MPa, irrespective of the coating hardness. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s11249-023-01804-6

Clarification of the Effect of Surface Energy on Tribological Behavior of Two-Phase Lubricant Using Reflectance Spectroscopy and Hydrodynamic Analysis Reviewed International coauthorship International journal

Hirata, K; Murashima, M; Umehara, N; Tokoroyama, T; Lee, WY; Hashizume, N; Sato, T; Nagata, R; Hanyuda, K; Otsuka, A; Ueda, M

TRIBOLOGY LETTERS Vol. 72 ( 1 ) 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology Letters

Recently, a new type of lubricant called two-phase lubricants has been developed to realize a high viscosity index. Two-phase lubricants are mixtures of two different lubricants, realizing low viscosity even at low temperatures due to the temperature dependence of the solubility of the lubricant molecules. In the present paper, the effect of surface energy on the tribological behavior of the two-phase lubricant is clarified using in situ observation with reflection spectroscopy. Sliding surfaces with high hydrogen-bonding terms in the surface energy components attracted high-polar lubricants, resulting in reduced friction. Analysis of the theoretical friction coefficient using Couette flow assumption revealed an important design concept of two-phase lubricants: the concentration of high viscosity lubricants on solid surfaces develops a viscosity distribution in the oil film, resulting in reduced friction.

DOI： 10.1007/s11249-023-01827-z

Effect of the graphite domain direction on the friction coefficient of tetrahedral amorphous carbon nitride Reviewed International journal

Tokoroyama T., Fujiwara C., Murashima M., Yamaguchi M., Umehara N.

Diamond and Related Materials Vol. 143 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Diamond and Related Materials

Polarized surface-enhanced Raman scattering was applied to low- and high- friction surfaces of tetrahedral amorphous carbon nitride (ta-CNx) to reveal the presence of the graphite structure and investigate the angular dependence of the graphite domains that formed on the topmost surface. The measured D peak intensity differed along the incident electric field toward the sliding direction, from parallel to perpendicular and armchair edges may be present. The results for the low- friction surface indicated that graphite domains exist on the ta-CNx disk and transfer layer on the counter material (Si3N4) ball in directions different from the sliding friction, which suggests an incommensurate configuration.

DOI： 10.1016/j.diamond.2024.110853

In situ Observation of the Formation of MoDTC-Derived Tribofilm on a Bearing Steel with Different Surface Roughness by Using a Reflectance Spectroscopy and Its Effects on Friction Reviewed International coauthorship International journal

Hashizume, N; Tokoroyama, T; Umehara, N; Murashima, M; Lee, WY; Zhang, RX; Kunisu, M; Shioji, H; Oharada, K

TRIBOLOGY LETTERS Vol. 72 ( 1 ) 2024.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology Letters

In this paper, we evaluated the formation of MoDTC-derived tribofilm and its effects on friction reduction. We conducted in situ observation using reflectance spectroscopy to monitor the tribofilm's evolution during friction, allowing us to estimate its thickness and composition. The results revealed that the rough specimen (Ra= 12.7 nm) maintained a smaller friction coefficient and a larger volume fraction of MoS2 compared to the smooth specimen (Ra= 2.6 nm). Additionally, using the in situ observed composition and contact state, we inferred changes in the frictional properties of the tribofilm formed on both specimens. This analysis suggested that the pronounced direct contact of asperities, especially evident in the rough specimen, promoted the formation of a low-friction tribofilm (primarily MoS2), enabling the rough specimen to sustain lower friction. Graphical abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s11249-023-01810-8

The 1 μm wear particles entrainment in situ observation via fluorescent staining silica particles by silane coupling with Rhodamine B Reviewed

Synthesising graphene with renewably-sourced bio-carbon precursors: a brief review Reviewed International coauthorship International journal

Abd Rahman F.H., Amiruddin H., Abdollah M.F.B., Mohd Zulkifli N.W., Samion S., Umehara N., Tanemura M., Honda M., Morina A.

Journal of the Brazilian Society of Mechanical Sciences and Engineering Vol. 46 ( 3 ) 2024.3

The Effect of Carbon Structure of DLC Coatings on Friction Characteristics of MoDTC-Derived Tribofilm by Using an In Situ Reflectance Spectroscopy Reviewed International coauthorship International journal

Hashizume, N; Yamamoto, Y; Chen, C; Tokoroyama, T; Zhang, RX; Diao, DF; Umehara, N

TRIBOLOGY LETTERS Vol. 72 ( 1 ) 2024.3

Tokoroyama, T; Okashita, M; Fusetani, N; Murashima, M; Hashizume, N; Tsuboi, R; Shiomi, H; Umehara, N

FRONTIERS IN MECHANICAL ENGINEERING-SWITZERLAND Vol. 10 2024.2

SURFACE & COATINGS TECHNOLOGY Vol. 477 2024.2

Development of an Electrocautery Surface Coating Method to Suppress Surgical Smoke Reviewed

Takayuki Tokoroyama, Motoyuki Murashima, Koki Ogawa, Noritsugu Umehara,

Journal of Surgery and Research 2024.1

Nitrogen-containing diamond-like carbon deposited on glass substrate via filtered cathodic vacuum arc with high-frequency pulsed DC substrate bias Reviewed International coauthorship International journal

Kim, JI; Lee, WY; Tanaka, K; Tokoroyama, T; Murashima, M; Umehara, N

SURFACES AND INTERFACES Vol. 44 2024.1

Creation of anti-frost micro-plastic texture surfaces enhancing thermal conductivity by carbon black containing in polyvinyl chloride Reviewed

TOKOROYAMA Takayuki, ZHANG Liying, WU Wenjun, MURASHIMA Motoyuki, UMEHARA Noritsugu

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 18 ( 3 ) page： JAMDSM0032 - JAMDSM0032 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Frost formation poses challenges in various sectors, impacting efficiency and safety. Active methods involve energy-consuming processes like heating, while passive approaches utilize protective coatings or hydrophobic surfaces to minimize frost aggregation. However, low thermal conductivity remains a concern. In previous research, lotus leaves inspired micro-meter-sized asperities were effective in controlling frost growth. Applying this concept to plastic, particularly low-cost PVC, raised challenges due to its low thermal conductivity. The study explores utilizing carbon black (CB) waste from hard coating processes to enhance PVC's thermal conductivity, forming a micro-plastic texture (MPT). The research investigates the influence of CB amount and AC voltage frequency on MPT features and thermal conductivity, aiming for a sustainable solution to address frost-related issues. Incorporating 0.9 vol.% CB into PVC solution under a 2 kV AC electric field (6 Hz) resulted in an extensively distributed MPT on the surface. This MPT, formed under the 6 Hz condition, exhibited no in-plane bias, making it an ideal surface for preventing frost formation. Adding CB to PVC within the range of 0 to 2.1 vol.% and applying a 2 kV, 6 Hz AC electric field led to independent MPT formation at concentrations between 0.4 to 1.2 vol.%. Conducting cooling tests in atmospheric and vacuum conditions, we found that MPT with 0.9 vol.% CB displayed a thermal conductivity of approximately 0.19 kW/mK in atmospheric conditions, similar to aluminum alloy. However, with 1.2 vol.% or more CB, it decreased to about 0.15 kW/mK. In vacuum conditions, MPT with 1.2 vol.% CB exhibited a higher thermal conductivity of 0.063 kW/mK compared to the 0.055 kW/mK observed in MPT with 0 vol.% CB.

DOI： 10.1299/jamdsm.2024jamdsm0032

Active control of Lubricant Flow Using Dielectrophoresis and Its Effect on Friction Reduction Reviewed

Murashima Motoyuki, Aono Kazuma, Umehara Noritsugu, Tokoroyama Takayuki, Lee Woo-Young

Tribology Online Vol. 18 ( 6 ) page： 292 - 301 2023.10

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

With the increasing demand for active friction control, we newly proposed to use dielectrophoresis to change the flow of PG-droplet-containing PAO4 to reduce the friction coefficient. The friction result with a 1-mm roller shows 20% reduction in friction coefficient (from 0.065 to 0.052) at AC 100 V, and in situ observation exhibits that PG tracks are formed over the contact area. On the other hand, at a high bias of 1000 V, the friction coefficient increases to 0.065. In this situation, in situ observation exhibits that PG forms a horseshoe-shaped track covering only the roller edges. Controlled friction tests and FEM analysis using 5-mm rollers revealed a unique behavior; a balanced bias effectively attracts the PG to the roller surface, and surface forces can resist mild dielectrophoretic forces to spread the PG across the roller surface. The present study strongly suggests the importance that the bias strength should be controlled to achieve a balance between surface force and dielectrophoretic force in order to obtain excellent lubrication conditions.

DOI： 10.2474/trol.18.292

Clarification of the effects of adsorption films of ester-blended oil on friction by in situ reflectance spectroscopy Reviewed International coauthorship International journal

Kodai Hirata, Motoyuki Murashima, Noritsugu Umehara, Takayuki Tokoroyama, Naoya Hashizume, Woo Young Lee, Daisuke Takekawa, Keiichi Narita

Tribology International Vol. 187 2023.9

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

In recent years, the demand for friction reduction in oil lubrication systems has become increasingly important due to the need to improve fuel economy and achieve carbon neutrality. Ester-based lubricants are known to show low friction and environmentally friendly, and they have high viscosity indexes. In the present paper, first, in situ reflectance spectroscopy was used to clarify the behavior of the oil-film thickness increase during sliding. The results showed that as the number of ester bonds increased from 1 to 4, the ester oil film thickened and the friction coefficient decreased from 0.10 to 0.06. In addition, oleic-acid-type lubricants were found to have superior ability to form a thicker oil film than the isostearic acid type.

DOI： 10.1016/j.triboint.2023.108718

Synthesis and characterisation of oil palm fibre-based graphene deposited on copper particles for superlubricity oil additive Reviewed International coauthorship International journal

Rahman Nurul Liyana, Amiruddin Hilmi, Bin Abdollah Mohd Fadzli, Umehara Noritsugu

JURNAL TRIBOLOGI Vol. 37 page： 128 - 141 2023.6

Effects of Phosphonate Additives with Hydroxy Groups on the Tribological Properties of ta-C Coatings Under Boundary Lubrication Reviewed International journal

Kento Tanaka, Takayuki Tokoroyama, Noritsugu Umehara, Motoyuki Murashima, Tadashi Oshio, Kazuhiro Yagishita

Tribology Letters Vol. 71 ( 2 ) 2023.6

Language：English Publishing type：Research paper (scientific journal)

Additives that are optimized for diamond-like carbon (DLC) coatings are highly demanded as their applications have expanded recently. In this study, friction tests were conducted on a tetrahedral amorphous carbon (ta-C)/ta-C tribopair using a phosphonate additive with hydroxy groups, which comprises glycerol monooleate (an additive that reduces the friction of DLC) and zinc dialkyl dithiophosphate (an additive that reduces wear), and the obtained tribolayers were analyzed using AFM, XPS, and ToF–SIMS. We found that the phosphonate additive with hydroxy groups tribochemically reacted with the ta-C coating to form a low-shear, hard tribolayer on the surface, thereby reducing the friction and wear of the ta-C coating. Our results indicate that additives with phosphonate structures and hydroxy groups are effective for DLC coatings. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s11249-023-01734-3

An effective strategy for improving the performance of electrodeposited Fe-W alloy plating: Tailoring microstructure by graphene incorporation Reviewed International coauthorship International journal

Shinohara Yu, Park Jae-Hyeok, Hagio Takeshi, Kim Jae-Il, Lee Woo-Young, Umehara Noritsugu, Ichino Ryoichi

MATERIALS & DESIGN Vol. 230 2023.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials and Design

Despite the excellent performance of hard Cr plating using hexavalent chromium (Cr6+), its use is being restricted owing to recent environmental regulations. Electrodeposited Fe-W alloy is considered a possible alternative, but its high coefficient of friction (COF), high wear rate owing to tribo-oxidation, and high corrosion rate hinder its practical application. In this study, we attempted to solve these problems by modifying the microstructure of Fe-W alloy by incorporating 2D-structured graphene. The effect of graphene incorporation on the structure of the Fe-W alloy and its properties, especially microhardness, wear, and corrosion resistance, were investigated. The results showed the graphene effectively modified the columnar structure of the Fe-W alloy by inhibiting the vertical growth of clusters during electrodeposition, leading to fragmentation of the vertical cluster boundaries. This improved the hardness by as much as 17 % up to 9.1 GPa, and the corrosion resistance by changing the corrosion mechanism from localized corrosion to uniform corrosion. In addition, the graphene reduced the COF and wear rate by reducing the Fe2O3 formed by tribo-oxidation to a lower oxidation state. The structural modification of the plating by graphene incorporation thus provides an effective solution to improving the performance of Fe-W alloys.

DOI： 10.1016/j.matdes.2023.111938

Synthesis and characterisation of oil palm fibre-based graphene deposited on copper particles for superlubricity oil additive Reviewed International coauthorship International journal

Rahman N.L., Amiruddin H., Abdollah M.F.B., Umehara N.

Jurnal Tribologi Vol. 37 page： 128 - 141 2023.6

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Jurnal Tribologi

This paper presents the synthesis and characterisation of oil palm fibre-based graphene deposited on copper (Cu) particles for superlubricity oil additive. Oil palm fibre (OPF) is employed as a renewable carbon feedstock to grow graphene on Cu particles during Chemical Vapor Deposition (CVD) process. The surface morphology was observed using Scanning Electron Microscopy (SEM) embedded with Energy Dispersive X-Ray Analysis (EDX), and Transmission Electron Microscopy (TEM). Meanwhile, the presence and quality of graphene were validated and examined using Gaussian analysis of Raman spectroscopy. The results show that decreasing the peak D to peak G intensity ratio (ID/IG) tends to improve graphene quality with less number density of structural defects. The I2D/IG value greater than 1 is indicative of multilayer graphene growth. Increasing the full width at half maximum (FWHM) ratio of peak D to peak G (FWHMD/FWHMG) suggests a better dispersion of graphene. The uniform spread of surface ‘wrinkles’ observed by SEM and TEM implies that the distribution of graphene is more homogeneous on the surface of Cu particles. Further investigation into the synergistic effect of graphene as an oil additive can be performed to achieve superlubricity properties.

Superlubricity with Graphitization in Ti-Doped DLC/Steel Tribopair: Response on Humidity and Temperature Reviewed International coauthorship International journal

Kim Jae-Il, Lee Woo-Young, Tokoroyama Takayuki, Umehara Noritsugu

ACS APPLIED MATERIALS & INTERFACES Vol. 15 ( 15 ) page： 19715 - 19729 2023.4

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Materials and Interfaces

The anti-friction of diamond-like carbon (DLC) is achieved by a well-developed carbonaceous transfer layer, and Ti-doped DLC is developed into a robustly built-up carbonaceous transfer layer. The friction performance of DLC depends on the operating environment, e.g., ambient gas, humidity, temperature, lubricants, and mating material. In this study, we aimed to reveal the environmental sensitivities of Ti-DLC on friction characteristics. To this end, a Ti-DLC was rubbed against a steel ball, and friction behaviors were evaluated with different gas compositions, humidity, and temperature. Finally, we identified that fractional coverage of water on surfaces affected the anti-graphitization on Ti-DLC, leading to avoiding friction reduction.

DOI： 10.1021/acsami.3c01704

Influence of Defects in Graphene-Like Network of Diamond-Like Carbon on Silica Scale Adhesion Reviewed International journal

Y. Nakashima, N. Umehara, H. Kousaka, T. Tokoroyama, M. Murashima, K. Murakami

Tribology Letters Vol. 71 ( 1 ) 2023.2

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

Silica scale adhesion onto geothermal power plant equipment reduces the power efficiency. In our previous study, diamond-like carbon (DLC) coatings with low sp2 fractions and high hydrogen contents were found to suppress silica adhesion. Therefore, the present study was aimed at clarifying the mechanism of silica adhesion onto the graphene-like network of DLC. In-lens scanning electron microscopic imaging of silica adhered onto defective graphene indicated that the adhesion occurred on defects in the graphene-like network. First-principles calculations revealed that the graphene with hydrogen-terminated defects exhibited reduced adsorption energy between silica and the graphene-like network. Overall, the simulations and experiments helped establish a silica adhesion model in which defects in the graphene-like network of DLC behave as silica adhesion sites. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s11249-022-01690-4

Novel friction stabilization technology for surface damage conditions using machine learning Reviewed International coauthorship International journal

Motoyuki Murashima, Takazumi Yamada, Noritsugu Umehara, Takayuki Tokoroyama, Woo Young Lee

Tribology International Vol. 180 2023.2

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

The surface damage is a serious cause of failure in tribosystems. In the present paper, we propose a new damage avoidance method that combines a contact position control system (e.g., morphing surface) and artificial-intelligence-based control (e.g., genetic algorithm: GA) to achieve stable friction and long life of sliding surfaces. In the case of the single-damage condition, the GA sequentially avoided contact with the damaged position, and finally complete damage avoidance was achieved. In the multiple-damage condition, we confirmed that learning by GA effectively stabilized friction, although the learning time was longer. In summary, the contact-position control method should provide new capabilities on real machine surfaces where unexpected damage occurs.

DOI： 10.1016/j.triboint.2023.108280

Long-term low-friction of Ti-overcoated and-doped DLCs: Robustly developed carbonous transfer layer with titanium Reviewed International coauthorship International journal

Kim Jae-Il, Lee Woo-Young, Tokoroyama Takayuki, Umehara Noritsugu

CARBON Vol. 204 page： 268 - 283 2023.2

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Carbon

Diamond-like carbon (DLC) has been under the research spotlight as an exceptional solid lubricant. Its friction performance is depending on a well-developed transfer layer upon its counterparts. Nowadays, iron-and brass-based metals have been utilized as the counterpart against DLC, however, it is reported their friction behaviors are somewhat inferior compared to titanium alloys. In this study, we tried to improve their friction behaviors and modified the contact interface from Fe/C to C/C by Ti addition in DLC. It was revealed that Ti, which has good adhesion for Fe and C, promoted the development of carbon transfer on Fe-based counterpart. Furthermore, Ti built-up a thick carbonous transfer layer and make better the friction performance of DLC sliding against Fe.

DOI： 10.1016/j.carbon.2022.12.012

Mechanical properties of maze-like carbon nanowalls synthesized by the radial injection plasma enhanced chemical vapor deposition method Reviewed International coauthorship International journal

Swapnil Ghodke, Motoyuki Murashima, Dennis Christy, Ngo Van Nong, Kenji Ishikawa, Osamu Oda, Noritsugu Umehara, Masaru Hori

Materials Science and Engineering: A Vol. 862 2023.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

The unique structural properties of vertically aligned graphene sheets or Carbon Nanowalls (CNWs) have attracted great interests for their potential for various applications in microelectronic devices, energy storage, and catalyst support materials. During the handling or operation of the devices, tension and/or pressure are often needed. Under such conditions, CNWs must undergo compression and stress. Therefore, the deformation mechanism and evolution behavior of the CNW structures under load play a critical role in the performance and reliability of the devices. In this study, the mechanical properties of a typical maze-like CNW structure synthesized by a Radial Injection Plasma Enhanced Chemical Vapor Deposition (RI-PECVD) technique were analyzed by employing the nanoindentation method. The measured compressive strength of the CNW structure was 50 MPa with an average modulus E value of ∼28 GPa, which is significantly higher than that of pyrolytic graphite and other graphene-based materials such as 3D graphene-derived carbon, commercial graphene, and reduced graphene oxide films. An elastoplastic behavior of a soft material was observed in high-resolution microscopy and a mechanism of deformation for CNWs is elucidated.

DOI： 10.1016/j.msea.2022.144428

Tribo-chemical wear of various 3d-transition metals against DLC: Influence of tribo-oxidation and low-shear transferred layer Reviewed International coauthorship International journal

Jae-Il Kim, Woo-Young Lee, Takayuki Tokoroyama, Motoyuki Murashima, Noritsugu Umehara

Tribology International Vol. 177 page： 107938 - 107938 2023.1

Carbon-based coatings for suppression of silica adhesion in geothermal power generation Reviewed International journal

Y. Nakashima, N. Umehara, H. Kousaka, T. Tokoroyama, M. Murashima, D. Mori

Tribology International Vol. 177 page： 107956 - 107956 2023.1

Essence of Tribology and Its Future Invited

UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 67 ( 12 ) page： 813 - 813 2022.12

The Tribological Property of a-C:H Coating with Tribolayer by Additive Having Glycerol and Phosphate Oxide Structure Reviewed International coauthorship International journal

Tokoroyama T., Tanaka K., Kani T., Murashima M., Lee W-Y, Umehara N., Oshio T., Yagishita K.

TRIBOLOGY LETTERS Vol. 70 ( 4 ) 2022.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Tribology Letters

The tribological properties of a-C:H coating sliding against a SUJ2 ball, a SUJ2 roller, and an a-C:H coated roller were investigated under temperatures ranging from 20 to 80 °C in PAO with different additives. The additives had a glycerol and hydroxyl functional group in one molecule to enhance additive adsorption for mating with the a-C:H coating disk material and to build a phosphorus oxide tribolayer. Additives with different numbers of hydroxyl groups and primary or secondary-type C6H13O structures were also prepared. The tribolayer derived from each additive was analyzed via EDS, XPS, and ToF-SIMS. XPS depth analysis for the tribolayers revealed that additives were dissociated by friction and suggested C–O bond cleavage occurred. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s11249-022-01659-3

Metal matrix nanocomposites in tribology: Manufacturing, performance, and mechanisms Reviewed International coauthorship

Pan Shuaihang, Jin Kaiyuan, Wang Tianlu, Zhang Zhinan, Zheng Long, Umehara Noritsugu

FRICTION Vol. 10 ( 10 ) page： 1596 - 1634 2022.10

New in situ low-friction technology for diamond-like carbon coatings using surface discharge treatment in ambient air Reviewed International coauthorship International journal

Motoyuki Murashima, Shintaro Oyama, Hiroyuki Kousaka, Takayuki Tokoroyama, Woo-Young Lee, Noritsugu Umehara

Tribology International Vol. 165 page： 107306 - 107306 2022.10

Friction characteristics of amorphous carbon coating against various 3d-transition metals Reviewed International journal

Jae Il Kim, Woo Young Lee, Takayuki Tokoroyama, Motoyuki Murashima, Noritsugu Umehara

Tribology International Vol. 174 2022.10

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

DLC has anti-friction characteristics due to the tribofilm formed by the carbon transfer to its mating material. However, its coefficient of friction depends on each mating material. This study aims to investigate a suitable mating material against diamond-like carbon coatings. We selected four 3d-transition metals (Ti, Fe, Ni and Cu) as the mating materials based on the chemical affinities for carbon, i.e., carbide formability and work of separation. Among them, Ti had the lowest coefficient of friction, followed by Fe, Ni and Cu. The structures of tribofilm formed on mating materials were characterized non-destructively using Raman spectroscopy consisting of confocal optics. It revealed that Ti could strongly attract the carbon and stably formed carbon-containing tribofilm, leading to low friction.

DOI： 10.1016/j.triboint.2022.107690

The tribological property of a-C:H coating with tribolayer by additive having glycerol and phosphate oxide structure Reviewed International journal

T. Tokoroyama, K. Tanaka, T. Kani, M. Murashima, W.Y. Lee, N. Umehara, T. Oshio, K. Yagishita

Tribology letters Vol. 70 page： 118 2022.10

The Effect of Rubber Deterioration on Static Friction on Metal Surfaces with Different Surface Roughness Characteristics Reviewed

MURASHIMA Motoyuki, SASO Tomohiro, UMEHARA Noritsugu, TOKOROYAMA Takayuki, HIRANO Ryo, OKIDATE Ryo

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 67 ( 9 ) page： 646 - 661 2022.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

Many studies on friction of rubber materials revealed the effect of power spectrum of surface roughness on friction. On the other hand, quantitative comparison of the effects of specific surface roughness parameters has not been sufficiently conducted as well as the effects of rubber deterioration on friction. In the present paper, the effect of rubber deterioration on static friction and its variation with surface profile (hard chromium (HCr) treatment, salt-bath nitrocarburizing (SBN) treatment, and gas nitrocarburizing (GN) treatment is clarified. The friction test results showed interesting results that the static friction coefficient of SBN surfaces decreased with rubber degradation, whereas the static friction coefficient of GN surfaces increased. Subsequently, we analyze the main characteristics of surface roughness parameters and explore the mechanism. First, due to the small skewness of the GN surface, the blockage of leakage channels is developed, resulting in the formation of oil reservoirs and a squeeze effect due to micro-slip of the rubber. Second, the surface of SBN has high peaks and the bearing area ratio of the peaks is high, which prevents the occurrence of leak-channel blockage and allows the peaks to penetrate rubber. The present paper specifically clarifies that these surface properties provide the obtained friction results.

DOI： 10.18914/tribologist.22-00001

Effect of fracture properties and surface morphology on wear of DLC coatings at severe contact condition Reviewed International coauthorship International journal

Yusei Yamada, Motoyuki Murashima, Noritsugu Umehara, Takayuki Tokoroyama, Woo Young Lee, Hajime Takamatsu, Yoshikazu Tanaka, Yoshiharu Utsumi

Tribology International Vol. 169 page： 107486 - 107486 2022.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV

The present study shows how the fracture properties and surface morphology of diamond-like carbon (DLC) coatings affect their wear properties. Nine types of DLC coatings with different carbonaceous structures and surface roughness were prepared. Fracture toughness was quantitatively evaluated from the crack length on the coatings. Subsequently, wear tests were conducted under boundary lubrication to evaluate the wear properties. The results showed that the wear rate of DLC coatings with rough surfaces decreased with increasing fracture toughness, while that of smooth DLC is independent of fracture toughness. In the DLCs with rough surface, it was found that brittle fracture occurred, and the fracture significantly increased the wear rate. Additionally, the ratio of the stress intensity factor to the fracture toughness value (K/KIC) was presented, showing comprehensive wear behaviors.

DOI： 10.1016/j.triboint.2022.107486

Development of a new diamond-like carbon surface treatment method with electric discharge for short running-in and friction reduction Reviewed International coauthorship International journal

Motoyuki Murashima, Misato Maeda, Deng Xingrui, Noritsugu Umehara, Hiroyuki Kousaka

Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology Vol. 236 ( 5 ) page： 1020 - 1030 2022.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

The present paper proposes a new treatment method for diamond-like carbon (DLC) coatings using electric discharge. DLC coatings exhibit excellent mechanical and tribological properties due to their unique carbonaceous structure. Several surface treatment methods were presented to achieve short running-in and low friction. However, in-situ surface treatment is needed to extend the life of machines and maintain their performance. Here, we propose an electric discharge treatment with a simple electrical circuit. As a result, the friction coefficient drastically drops from 0.3 to 0.11. Interestingly, the drop starts shortly after the discharge starts. Consequently, the running-in is shortened to about 6-m sliding compared to no discharge condition, which does not show any running-in more than 68-m sliding. Raman analysis reveals that a transfer layer on the ball surface is composed of carbonaceous material and the structure exhibits graphite-like characteristics. However, there is visible damage on the DLC surface. Another friction test shows a very low friction coefficient of 0.04 using a transfer layer-covered ball and a new DLC disk with a smooth surface. In conclusion, the combination of a transfer layer and smooth DLC surface is needed to exhibit excellent tribological performance, indicating the importance of less damage treatment. Next, pulse discharge treatment is demonstrated to achieve less damage to the DLC coating. As a result, the pulse discharge method reduces friction and surface damage. In conclusion, the proposed treatment methods using electric discharge not only show the potential for reducing friction, but also the feasibility of in-situ treatment during machine operation.

DOI： 10.1177/13506501211013126

Realization of near-less friction of ta-CNx coating under R32 refrigerant environment Reviewed International journal

Wooyoung Lee, Motoyuki Murashima, Noritsugu Umehara, Takayuki Tokoroyama, Norihisa Horaguchi, Takao Ishimoto

Tribology International Vol. 168 page： 107404 - 107404 2022.4

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV

Diamond-like carbon (DLC) has attracted attention from refrigeration industry due to their excellent tribological behaviors. This study focused on high friction-efficiency in hydrofluorocarbon (HFC) refrigerant, however, DLC coatings have not been achieved in previous research. We evaluated friction behavior of tetrahedral amorphous carbon nitride under difluoromethane (R32) and R32/polyolester (POE) mixture environment, respectively. Friction coefficients of 0.02 and 0.03 were recorded under R32 and R32/POE atmosphere, respectively. These results emphasize an importance of the tribofilm consisted of graphite-and polymer-like carbon, terminated with R32 components (C, H, and F).

DOI： 10.1016/j.triboint.2021.107404

Tribological Property of ta-CNx:Ta Deposited via Ion Beam Assisted-Filtered Arc Deposition Reviewed International journal

T. Tokoroyama, Y. Tagami, M. Murashima, W. Y. Lee, N. Umehara, H. Kousaka

Tribology International Vol. 168 page： 107450 - 107450 2022.4

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV

Improving the hardness of amorphous carbon nitride with tantalum was realized by using ion beam assisted filtered arc deposition to obtain a low friction coefficient and low specific wear rate in ambient air. The coatings were prepared with different nitrogen flow during coating at different discharge cycles of tantalum. The wear scar and as-deposited surfaces were observed and analyzed by means of FESEM, AES, XPS, and Raman analysis. The lowest friction coefficient (~0.07) was obtained for ta-C:Ta200, which exhibited a low specific wear rate of < 1.0 × 10−7 mm3/Nm. The XPS analysis revealed the existence of amorphous Ta2O5, and the friction coefficient seemed to be positively correlated with oxygen desorption from the coatings.

DOI： 10.1016/j.triboint.2022.107450

Relationship between Friction Coefficient of Carbonaceous Hard Coatings and Surface Energy of Friction Scar from Contact Angels of Condensed Liquid with ESEM Reviewed

UMEHARA Noritsugu, NAKAO Taichi, TERADA Makoto, KOUSAKA Hiroyuki, MURASHIMA Motoyuki

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 67 ( 2 ) page： 126 - 138 2022.2

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

Carbonaceous hard coatings have promising tribological properties, such as low friction, high hardness and high wear resistance. In particular, CNx (Carbon Nitride) coating and a-C:H (hydrogenated amorphous carbon) coating show ultra low friction coefficient (µ < 0.01) in dry nitrogen gas. However, the mechanism of ultra low friction has not clarified. We have developed the in-situ measurement method on friction area during sliding to clarify the ultra low friction mechanism of carbonaceous hard coating. In this research, we demonstrated in-situ measurement of surface energy on friction area during friction by manufacturing friction tester in ESEM (Environmental Scanning Electron Microscope) chamber. Moreover, we estimated the effect of surface energy on friction property of carbonaceous hard coatings. We used UV irradiation to prepare the carbonaceous hard coatings, which have different surface energy. From the results, friction coefficient of carbonaceous hard coating decreased with surface energy, however the approximate line which showed the relationship between friction coefficient and surface energy did not pass through the origin. It suggested that friction occurred beneath the sliding surface in coatings or transferred layers not on the surface. Moreover, surface energy of carbonaceous hard coatings approached the value of graphite when carbonaceous hard coatings showed low friction. It suggested that structure of carbonaceous hard coatings had become graphite-like structure.

DOI： 10.18914/tribologist.21-00018

Metal matrix nanocomposites in tribology: Manufacturing, performance, and mechanisms Reviewed International coauthorship International journal

Pan Shuaihang, Jin Kaiyuan, Wang Tianlu, Zhang Zhinan, Zheng Long, Umehara Noritsugu

Friction Vol. 10 page： 1596 - 1634 2022.1

The Tribological Properties of Hydrogenated DLC Coating Lubrication with Additive Having Glycerol and Phosphonate Structure Reviewed International journal

Kani T., Tokoroyama T., Umehara N., Murashima M., Lee W.Y., Yagishita K.

Vierteljahresschrift fur Sozial und Wirtschaftsgeschichte Vol. 108 ( 4 ) page： 263 - 270 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Vierteljahresschrift fur Sozial und Wirtschaftsgeschichte

In general, several mechanical parts are subjected to friction and wear. To prevent wear and high friction coefficient under lubrication, additives can work to reduce friction force, to build up thin film on surfaces which is so-called tribofilm. Recently, Diamond-Like Carbon (DLC) is focused because it has excellent low friction and high wear proof as solid lubricant. However, several researchers already reported that tetrahedral amorphous carbon (ta-C) showed abnormal wear when it rubbed with glycerol mono-oleate (GMO) that is a kind of additive, although it showed very low friction coefficient. To improve tribological properties, new additives were developed that had both phosphate-oxide structure derived from ZnDTP which had high wear resistance and hydroxy group derived from GMO in one structure. To clarify the effects of the additives, friction tests were performed fixed-roller-on-disk type rotating friction tester. In the friction tests, hydrogenated amorphous carbon (a-C:H) disks, and a-C:H coated rollers were used under boundary lubrication condition at 20-80°C. Friction tests were conducted in Poly-α-olefin (PAO) oil with each GMO and the additives. The results exhibited that a-C:H gave ultra-low friction with the additive. Elemental analysis of the surface showed that tribofilm of phosphorus and oxygen was detected on the a-C:H surface in the additive used condition.

DOI： 10.25162/VSWG-2021-0016

In situ observation of the formation of MoDTC-derived tribofilm on a ta-C coating using reflectance spectroscopy and its effects on friction Reviewed International coauthorship International journal

Naoya Hashizume, Motoyuki Murashima, Noritsugu Umehara, Takayuki Tokoroyama, Woo-Young Lee

TRIBOLOGY INTERNATIONAL Vol. 162 page： 107128 2021.10

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

We clarify the relationships between tribofilm thickness, chemical composition, and friction coefficient by combining in situ and ex situ analyses. An in situ reflectance observation is conducted for MoDTC-derived tribofilm on a ta-C coating during friction tests. The results show that the thicker the tribofilm is, the lower the friction coefficient. In addition, the refractive index increases as friction decreases. XPS analysis shows that the topmost surface of the thick tribofilm contains a higher MoS2 concentration than the deep position. Therefore, the generated MoS2-rich tribofilm is considered to reduce friction. In addition, as the MoS2 tribofilm wears out, friction increases. In conclusion, we have developed a MoDTC-derived tribofilm formation model using a new method of in situ optical measurement.

DOI： 10.1016/j.triboint.2021.107128

The Tribological Properties of Hydrogenated DLC Coating Lubrication with Additive Having Glycerol and Phosphonate Structure Reviewed

Improved wear imbalance with multilayered nanocomposite nanocrystalline Cu and tetrahedral amorphous carbon coating Reviewed International coauthorship

Kim Jae-Il, Kim Jongkuk, Kim Do Hyun, Jang Young-Jun, Umehara Noritsugu

CERAMICS INTERNATIONAL Vol. 47 ( 18 ) page： 25664 - 25673 2021.9

KANI Takumi, TOKOROYAMA Takayuki, UMEHARA Noritsugu, MURASHIMA Motoyuki, LEE Woo-Young, YAGISHITA Kazuhiro

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 66 ( 7 ) page： 570 - 578 2021.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In general, several mechanical parts are subjected to friction and wear. To prevent wear and high friction coefficient under lubrication, additives can work to reduce friction force, to build up thin film on surfaces which is so-called tribofilm. Recently, Diamond-Like Carbon (DLC) is focused because it has excellent low friction and high wear proof as solid lubricant. However, several researchers already reported that tetrahedral amorphous carbon (ta-C) showed abnormal wear when it rubbed with glycerol mono-oleate (GMO) that is a kind of additive, although it showed very low friction coefficient. To improve tribological properties, new additives were developed that had both phosphate-oxide structure derived from ZnDTP which had high wear resistance and hydroxyl group derived from GMO in one structure. To clarify the effects of the additives, friction tests were performed fixed-roller-on-disk type rotating friction tester. In the friction tests, hydrogenated amorphous carbon (a-C:H) disks, and a-C:H coated rollers were used under boundary lubrication condition at 20-80°C. Friction tests were conducted in Poly-α-olefin (PAO) oil with each GMO and the additives. The results exhibited that a-C:H gave ultra-low friction with the additive. Elemental analysis of the surface showed that tribofilm of phosphorus and oxygen was detected on the a-C:H surface in the additive used condition.

DOI： 10.18914/tribologist.21-00001

Wear acceleration of a-C:H coatings by molybdenum-derived particles: Mixing and temperature effects Reviewed International journal

K. A.M. Kassim, T. Tokoroyama, M. Murashima, W. Y. Lee, N. Umehara, M. M.B. Mustafa

Tribology International Vol. 159 page： 106944 - 106944 2021.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier BV

MoDTC has also been reported to degrade into other Mo-derived compounds. It is essential to analyze the effects of each type of MoDTC-degraded material on DLC. Therefore, we chose powder-type MoDTC, MoS2, Mo, MoO3, and Mo2C additives to be dispersed individually into a base oil and tested on an a-C:H sliding against a steel ball under boundary lubrication conditions at 80 °C. We then obtained surface-enhanced Raman scattering (SERS), which proved that MoS2 has the possibility of extracting hydrogen from the topmost surface as chemical wear (hydrogen content decreased from 30 to 35 at.% to 20 at.% of as-deposited) and that MoO3, MoDTC, and Mo have the possibility of catalytic reactions with carbon atoms. Mo2C exhibited abrasive accelerate of the a-C:H wear.

DOI： 10.1016/j.triboint.2021.106944

Evaluation of Mechanical Characteristics of Tribofilm Formed on the Surface of Metal Material Due to Friction under Lubrication with Automatic Transmission Fluid Reviewed

TOKOROYAMA Takayuki, NISHIMOTO Takashi, MURAKAMI Yasuhiro, HONDA Akiyuki, MITSUI Hideaki, TERAI Yusuke, MURASHIMA Motoyuki, LEE Woo-Young, UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 66 ( 6 ) page： 461 - 469 2021.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In this study, nano-scratch tests were conducted using atomic force microscope (AFM) to clarify the hardness of a tribofilm derived from an additive (Fluid A or Fluid B in automatic-transmission fluid) formed on an SKS3 cold work tool steel substrate surface. Comparisons between nano-indentation hardness tests and AFM nano-scratch tests were performed for each specimen. Prior to these tests, the tribofilms on the SKS3 substrate were examined with energy-dispersive spectroscopy (EDS). In order to calculate the hardness of the tribofilm from the nano-scratch results, we assumed that the AFM diamond tip acted as an abrasive to plough the tribofilm. The phosphorus-derived tribofilm formed from Fluid A was harder than the sulfur-derived tribofilm from Fluid B, and it was calculated that the phosphorus-derived tribofilm was approximately 2.64 GPa and the sulfur-derived tribofilm was 1.89 GPa. After 10 nano-indentation hardness tests on each tribofilm, the maximum indentation depth into the tribofilm formed from Fluid A was approximately 31 nm, while it was approximately 36 nm for Fluid B. These results are qualitatively consistent with the hardness results obtained by the AFM nano-scratch test method.

DOI： 10.18914/tribologist.20-00020

Realization of A Novel Morphing Surface using Additive Manufacturing and its Active Control in Friction Reviewed International journal

Motoyuki Murashima, Yusuke Imaizumi, Masato Kawaguchi, Noritsugu Umehara, Takayuki Tokoroyama, Toshiyuki Saito, Masayuki Takeshima, Yosuke Tsukiyama, Isami Nitta

ASME, Journal of Tribology Vol. 143 ( 5 ) page： 1 - 29 2021.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ASME International

<title>Abstract</title>
As the need for higher efficiency of engineering components increases, so does the demand for functional surfaces. While various tribosurfaces (e.g., texturing and coatings) have been developed, many researches are aimed at static functionality. On the other hand, due to a wide range of environmental adaptability and active control, active-morphing surfaces can be highly efficient and robust. In this paper, we demonstrate a novel morphing surface and its realization using additive manufacturing (AM). By using a diaphragm structure, morphing performance is achieved even if a hard resin material is used. When air pressure is applied to the backside of the diaphragm, it changes to a convex shape, and vice versa. The concept requires a complex structure for arranging airflow and a solid morphing system. The AM is one great technique to create such complex structure. As a result of actual manufacturing, the created morphing structure realizes a large morphing of 600 µm or more. In addition, the shape changes reversibly depending on the air pressure. The surface also exhibits very interesting tribological characteristics. The surface shows a friction coefficient of 0.5-1.7 with a convexity, and then decreases to about 0.3 with a concavity. A real-contact area measurement reveals that the novel property occurs due to change in the real-contact area depending on surface morphology. In conclusion, the present paper provides a new concept of a novel morphing tribosurface, which selectively performs as a low-friction or break-like surface, created using AM.

DOI： 10.1115/1.4050269

Active Friction Control in Lubrication Condition Using Novel Metal Morphing Surface Reviewed International journal

M. Murashima, T.Tokoroyama, N. Umehara

Tribology International Vol. 156 page： 1 - 9 2021.5

Nanotextured Mold Surface with DLC Coating for Reduction in Residual Ceramic Particles Reviewed International journal

Motoyuki Murashima, Koki Hojo, Shigehiro Ito, Noritsugu Umehara, Takayuki Tokoroyama, Tomonori Takahashi, Minoru Imaeda

LANGMUIR Vol. 37 ( 12 ) page： 3563 - 3574 2021.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

In the ceramic industry, ceramic particles remain on a mold surface due to which the mold requires frequent cleaning during press molding, reducing productivity. Surface texturing and tetrahedral amorphous carbon (ta-C) coatings are well-known surface-energy controllable treatments developed for low adhesion, low friction, and high wear resistance. In the present paper, we demonstrate the effect of reducing ceramic residues using nanotexturing, ta-C coatings, and their combination. We compare two surface morphologies (i.e., 770 nm pitch nanotexturing and flat) and five materials (i.e., nonhardened steel, hardened steel, ta-C, and two types of nitrogen-doped ta-C (ta-CNx). Molding test results show that the ta-C coating on flat surfaces with the highest hardness of 30 GPa shows the lowest residual amount of 5.9 mu g for Al2O3 ceramic particles. The amount is 82% less than that of the nonhardened steel. The ta-CNx(20), made with a nitrogen flow rate of 20 sccm, shows the lowest residual amount of 234 mu g for SiO2 ceramic particles, which is 81% less than that of the nontextured ta-CNx(20). In conclusion, we provide design guidelines for nanotextured mold surfaces including the texturing pitch should be small enough for ceramic particles; the mold surface should be sufficiently hard; the lower the surface energy per unit area, the less residues of ceramic particles.

DOI： 10.1021/acs.langmuir.0c03435

The Clarification of Friction Mechanism in Oil Lubrication for CNx Coating by In-Situ Observation of Friction Area with Reflectance Spectroscopy Reviewed International journal

Okamoto Tatsuya, Umehara Noritsugu, Murashima Motoyuki, Saito Koji, Manabe Kazuyoshi, Hayashi Keiji

Tribology Online Vol. 16 ( 1 ) page： 49 - 58 2021

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

To clarify the low friction mechanism of CNx coating in PAO oil lubrication, we measured reflectance spectrum at friction area in-situ by reflectance spectroscopy during friction test against a sapphire hemisphere pin in PAO oil. We observed and estimated the thickness of PAO oil film, the surface roughness of CNx coating, thicknesses, and polarizability of the transformed layer formed on bulk CNx coating during friction test by analyzing reflectance spectrum. We proposed that the decreasing of load ratio of boundary lubrication mode to total load is the one of governing factor to reduce friction on the basis of the increasing of Λ value. Also we proposed the increasing of adsorption of PAO oil to the CNx transformed layer is the second governing factor on the basis of the increasing of polarizability of PAO oil and transformed layer, that leads to the increasing of van der Waals force between transformed layer and PAO oil as low friction mechanism of CNx in PAO oil lubrication.

DOI： 10.2474/trol.16.49

Evaluation of Mechanical Characteristics of Tribofilm Formed on the Surface of Metal Material Due to Friction under Lubrication with Automatic Transmission Fluid Reviewed International journal

Tokoroyama Takayuki, Nishimoto Takashi, Murakami Yasuhiro, Honda Akiyuki, Mitsui Hideaki, Terai Yusuke, Murashima Motoyuki, Lee Woo-Young, Umehara Noritsugu

Tribology Online Vol. 16 ( 4 ) page： 255 - 262 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In this study, nano-scratch tests were conducted using atomic force microscope (AFM) to clarify the hardness of a tribofilm derived from an additive (Fluid A or Fluid B in automatic-transmission fluid) formed on an SKS3 cold work tool steel substrate surface. Comparisons between nano-indentation hardness tests and AFM nano-scratch tests were performed for each specimen. Prior to these tests, the tribofilms on the SKS3 substrate were examined with energy-dispersive spectroscopy (EDS). In order to calculate the hardness of the tribofilm from the nano-scratch results, we assumed that the AFM diamond tip acted as an abrasive to plough the tribofilm. The phosphorous-derived tribofilm formed from Fluid A was harder than the sulfur-derived tribofilm from Fluid B, and it was calculated that the phosphorous-derived tribofilm was approximately 2.64 GPa and the sulfur-derived tribofilm was 1.89 GPa. After 10 nano-indentation hardness tests on each tribofilm, the maximum indentation depth into the tribofilm formed from Fluid A was approximately 31 nm, while it was approximately 36 nm for Fluid B. These results are qualitatively consistent with the hardness results obtained by the AFM nano-scratch test method.

DOI： 10.2474/trol.16.255

The Tribological Properties of Hydrogenated DLC Coating Lubrication with Additive Having Glycerol and Phosphonate Structure Reviewed International coauthorship International journal

Kani Takumi, Tokoroyama Takayuki, Umehara Noritsugu, Murashima Motoyuki, Lee Woo-Young, Yagishita Kazuhiro

Tribology Online Vol. 16 ( 4 ) page： 263 - 270 2021

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In general, several mechanical parts are subjected to friction and wear. To prevent wear and high friction coefficient under lubrication, additives can work to reduce friction force, to build up thin film on surfaces which is so-called tribofilm. Recently, Diamond-Like Carbon (DLC) is focused because it has excellent low friction and high wear proof as solid lubricant. However, several researchers already reported that tetrahedral amorphous carbon (ta-C) showed abnormal wear when it rubbed with glycerol mono-oleate (GMO) that is a kind of additive, although it showed very low friction coefficient. To improve tribological properties, new additives were developed that had both phosphate-oxide structure derived from ZnDTP which had high wear resistance and hydroxy group derived from GMO in one structure. To clarify the effects of the additives, friction tests were performed fixed-roller-on-disk type rotating friction tester. In the friction tests, hydrogenated amorphous carbon (a-C:H) disks, and a-C:H coated rollers were used under boundary lubrication condition at 20-80°C. Friction tests were conducted in Poly-α-olefin (PAO) oil with each GMO and the additives. The results exhibited that a-C:H gave ultra-low friction with the additive. Elemental analysis of the surface showed that tribofilm of phosphorus and oxygen was detected on the a-C:H surface in the additive used condition.

DOI： 10.2474/trol.16.263

The Clarification of Friction Mechanism for Carbonaceous Hard Coatings by in-situ Observation of Friction Area with Reflectance Spectroscopy Invited

New study on tribological performance of AA7075-TiB2 nanocomposites Reviewed International coauthorship

Pan Shuaihang, Saso Tomohiro, Yu Ning, Sokoluk Maximilian, Yao Gongcheng, Umehara Noritsugu, Li Xiaochun

TRIBOLOGY INTERNATIONAL Vol. 152 2020.12

The Clarification of Friction Mechanism in Oil Lubrication for CNx Coating by In-Situ Observation of Friction Area with Reflectance Spectroscopy Invited

UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 65 ( 11 ) page： 684 - 687 2020.11

ポリ塩化ビニル溶媒への交流電場援用マイクロプラスチック突起の創製 Reviewed

山田雄聖，野老山貴行，村島基之，梅原徳次

日本機械学会論文集 Vol. 86 ( 892 ) page： 20-00228 2020.11

Re-Organization of Technical Support Staffs in Nagoya University Invited

UMEHARA Noritsugu, KOGA Kazushi, FUJIWARA Fumiharu, SAWAKI Koji, YAMAMOTO Kouji, TACHIBANA Kazushi, MIZUGUCHI Ikuyo

Journal of the Japan Society for Precision Engineering Vol. 86 ( 9 ) page： 662 - 665 2020.9

UMEHARA Noritsugu

Journal of The Surface Finishing Society of Japan Vol. 71 ( 9 ) page： 547 - 550 2020.9

コーティング電気メス先端の炭化物付着抑制手法の開発 Reviewed

野老山貴行，小林将大，村島基之，梅原徳次，小川航生，萬隆行，内田淳一

日本機械学会論文集 Vol. 86 page： 20-00273 2020.9

Enhancement of speed of surface roughness improvement by using a two mixed abrasive slurry method to polish glass surfaces Reviewed

TAKENO Hiroaki, TOKOROYAMA Takayuki, MURASHIMA Motoyuki, UMEHARA Noritsugu, CHIBA Shogo

Journal of the Japan Society for Abrasive Technology Vol. 64 ( 8 ) page： 428 - 435 2020.8

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society for Abrasive Technology

This study was performed to find a method to reduce the consumption of expensive diamond abrasive grains in polishing glass substrates, and to mix low-hardness abrasives with diamond abrasives to reduce costs and achieve early improvement of surface roughness. The effects of the size of the GC abrasives (approximately 127 μm, 75 μm, and 13 μm), abrasive concentration, and types of abrasives (WA and B4C) were clarified for low-hardness abrasives. The abrasive grains were fluorescently stained with rhodamine B to determine their behavior on the polished surface in-situ. The results indicated improved surface roughness by using two types of mixed abrasive grains. In addition, the large-grain GC abrasives moved or were shown to be trapped in the gaps of the fibers of the natural silk polishing pad used for polishing. On the other hand, diamond grains with an average grain size of 1.0 μm moved between the natural silk polishing pad and the glass substrate regardless of the fiber orientation.

DOI： 10.11420/jsat.64.428

CiNii Books

金ナノ粒子法を用いた表面増強ラマン分析による炭素系薄膜の極表面分析 Reviewed

野老山貴行，梅原徳次，村島基之

トライボロジスト Vol. 65 ( 8 ) page： 517 - 525 2020.8

New study on tribological performance of AA7075-TiB2 nanocomposites Reviewed International coauthorship International journal

Shualihang Pan, Tomohiro Saso, Ning Yu, Maximillan Sokoluk, Gongcheng Yao, Noritsugu Umehara, Xiaochun Li

Tribology International Vol. 152 page： 106565 2020.8

The wear classification of MoDTC-derived particles on silicon and hydrogenated diamond-like carbon at room temperature Reviewed International journal

K. A.M. Kassim, T. Tokoroyama, M. Murashima, N. Umehara

Tribology International Vol. 147 page： 106176 2020.7

Language：English Publishing type：Research paper (scientific journal)

Molybdenum dithiocarbamate (MoDTC) is well-known as a friction-modifier in engine oil but has wear accelerating effects on DLC/steel sliding contact. Since MoDTC was reported degradable to other materials, the effect of each material on wear acceleration has not been clarified yet. Therefore, it is necessary to divide which Mo-derived compound has a major role to enhance wear. Thus, powder-type MoDTC, MoO3, Mo2C, MoS2, and Mo were dispersed into Poly-alpha-olefin (PAO), and tested on a-C:H and Si-DLC against steel ball at room temperature. For Mo2C, MoDTC, and MoO3, the specific wear rate of a-C:H was approximately 3.4 × 10−5, 3.2 × 10−6 and 1.5 × 10−6 mm3/Nm, respectively. MoDTC indicated higher affection than MoO3 regardless of the particles’ hardness. Si-DLC showed better wear prevention compared to a-C:H.

DOI： 10.1016/j.triboint.2020.106176

Effect of mesh structure of tetrahedral amorphous carbon (ta-C) coating on friction and wear properties under base-oil lubrication condition Reviewed International coauthorship International journal

Mohd Muhyiddin Bin Mustafa, Noritsugu Umehara, Takayuki Tokoroyama, Motoyuki Murashima, Akinori Shibata, Yoshiharu Utsumi, Hideki Moriguchi

TRIBOLOGY INTERNATIONAL Vol. 147 page： 105557 2020.7

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

This study examined the tribological properties of novel mesh tetrahedral amorphous carbon (Mesh ta-C). Subsequently, comparison was made with conventional ta-C and a-C:H coatings under base-oil lubrication via cylindrical-pin-on-disk tribo-tester. Analysis of wear track was conducted using field-emission-scanning-electron-microscope (FE-SEM), atomic-force-microscopy (AFM), and Raman-spectroscopy. The friction coefficient for Mesh ta-C and conventional ta-C revealed a similar pattern with regard to loads. The Mesh ta-C had excellent wear resistance, where the wear rates at loads of 20 N was five and 20 times lower than conventional a-C:H and ta-C, respectively. High wear resistance of Mesh ta-C characterized by inhibition of brittle micro-fracture propagation, less in abrasive particle created during friction test, and suppressing the effect of graphitization-induced wear on the contact surface.

DOI： 10.1016/j.triboint.2019.01.016

Effect of defects on wear behavior in ta-C coating prepared by filtered cathodic vacuum arc deposition Reviewed International coauthorship International journal

Woo-Young Lee, Young-Jun Jang, Takayuki Tokoroyama, Motoyuki Murashima, Noritsugu Umehara

DIAMOND AND RELATED MATERIALS Vol. 105 page： 107789 - 107789 2020.5

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

This study examined the tribological behavior of a ta-C coating fabricated at a substrate bias of -100 V via filtered cathodic vacuum arc (FCVA) deposition. Defects in the ta-C coating were categorized as droplets, pores, and spikes, considering the morphological, structural, and mechanical properties of the ta-C surface. A friction test was conducted at 170 degrees C in ambient air using a ball-on-disk tribometer. The friction coefficient was 0.08 during the steady state and the wear rate was 4.3 x 10(-6) mm(3)/Nm. To explain the friction and wear behavior, the morphological and structural properties of the defects in the designated area were compared among different sliding cycles.

DOI： 10.1016/j.diamond.2020.107789

The Surface Enhanced Raman Scattering Analysis for Carbonaceous Coating by Using Au Nano-Particles Reviewed International journal

T. Takayuki, M. Murashima, N. Umehara

TRIBOLOGY ONLINE Vol. 15 ( 5 ) page： 300 - 308 2020.5

Tribology in Shaver

TOKOROYAMA Takayuki, UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 65 ( 4 ) page： 236 - 241 2020.4

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

From time immemorial, shaving one’s beard has been continued. Using razor or electric shaver is common for all male adult to show their cleanliness recently. The custom for shaving my beard by myself was harbingered by World War I and II. Tremendous safety razors were provided by US government to frontline infantry, then they acquired a custom of “shaving by myself”. An electric shaver was invented early of the 20th century, and it is divided two shaving motion, a rotation or a reciprocation. In this article, investigating the relation between inner blade’s edge radiuses and pulling force, clarifying differences of shaving mechanism of a rotation or a reciprocation type shaver by a high speed camera with measuring pulling force simultaneously are explained.

DOI： 10.18914/tribologist.65.04_236

New Droplet Removal Polishing Method for Diamond-Like Carbon with Carbon Fiber Brush Reviewed International journal

Murashima Motoyuki, Imaizumi Yusuke, Umehara Noritsugu, Tokoroyama Takayuki

International Journal of Automation Technology Vol. 14 ( 2 ) page： 190 - 199 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Fuji Technology Press Ltd.

In this paper, we propose a new polishing method for diamond-like carbon (DLC) coatings using a carbon fiber brush (CFB). Surface finishing is an important process for DLC coating applications. A lapping process is widely used for attaining tetrahedral amorphous carbon (ta-C) coatings, which are a type of DLC coating containing many droplets, to obtain fine flat surfaces. The lapping process removes protuberant parts of droplets rather than the entire droplet. In this paper, we propose a new polish brush material made of carbon fiber, called CFB. Carbon fiber has both mechanical strength due to its hard carbonaceous material and flexibility due to its fiber structure. In polishing tests, CFB removed droplets from ta-C coatings and the removal effect increased with the shortening of the brush length. The surface profiles of the polished surfaces indicated that a shorter brush length yielded deep scratch marks on ta-C surfaces. Consequently, the arithmetic average surface roughness of the polished ta-C surfaces, Sa, had almost the same value as that of a non-polished surface. Here, we show the ability of CFB to remove the droplets without an increase in the surface roughness. The CFB with the longest brush length in the present study (12 mm) showed a ten-point average roughness SZJIS= 75 nm and Sa= 4.7 nm, which were 59% and 22% lower than those of the non-polished surface, respectively. Furthermore, the longest CFB removed the entire droplets whereas a shorter CFB merely removed the protuberant part of the droplets. The result indicates that CFB polishing can remove entire droplets, which result in abrasive wear or deterioration. From other polishing tests, the optimum polishing distance was determined. Shorter polishing distances could not remove droplets sufficiently whereas longer polishing distances caused deep scratches on ta-C surfaces due to the material transferred to the CFB. Accordingly, the polishing distance of 600 m showed the best surface finishing with SZJIN= 25 nm and Ra= 0.43 nm, which were 86% lower than and similar to those of the non-polished ta-C surface, respectively.

DOI： 10.20965/ijat.2020.p0190

二液分離油の反射分光摩擦面その場観察装置を用いたしゅう動部油膜その場分析 Reviewed

山田高澄, 梅原徳次, 野老山貴行, 村島基之, 佐藤卓, 大原健司, 羽生田清志

日本機械学会論文集 Vol. 86 ( 884 ) page： 1900315 2020.3

ディーゼルエンジンオイル中ナノメートルサイズPMの交流電場による凝集を用いたろ過手法の開発 Reviewed

野老山貴行, 柴沢穂高, 梅原徳次

日本機械学会論文集 Vol. 86 ( 884 ) page： 2000016 2020.3

Development of Surface Roughness Generation Model for CFRTP Manufactured by LFT-D Reviewed International journal

Murashima Motoyuki, Murooka Takaharu, Umehara Noritsugu, Tokoroyama Takayuki

International Journal of Automation Technology Vol. 14 ( 2 ) page： 208 - 216 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Fuji Technology Press Ltd.

In this study, we propose a new surface generation model for carbon fiber reinforced thermoplastics (CFRTP) manufactured by the long fiber thermoplastic-direct (LFT-D) method. CFRTP are considered to be a next-generation structural material because of their high productivity as well as high mechanical strength and lightness. Conversely, CFRTP have a rough surface, which does not meet the automotive outer panel standard of a “class A surface.” In the present study, we establish a surface roughness generation model based on a thermal shrinkage mismatch of thermoplastic resin to carbon fiber and non-uniform carbon fiber distribution. Furthermore, we construct a surface roughness estimation formula based on the model. In the calculation, a cross-sectional image of CFRTP is divided into many vertical segments. Subsequently, the thermal shrinkage of each segment is calculated with a standard deviation, an average, and a probability density of the amount of carbon fiber in each segment. The surface roughness of the manufactured CFRTP was measured using a surface profilometer. The result showed that the arithmetic surface roughness increased with the volume fraction of carbon fiber. We applied the surface roughness calculation to cross-sectional images of the specimens. Consequently, the estimated surface roughness showed the same tendency, in which the surface roughness increased with the volume fraction of carbon fiber. The slope of a regression line of the estimated surface roughness with respect to the volume fraction was 0.010, which was almost the same (0.011) as the slope of a regression line of the measured surface roughness. Furthermore, the estimation formula using a thermal shrinkage effective depth of 395 μm was able to estimate the surface roughness within a 3% average error. Using the estimation formula, it was predicted that the surface roughness increased with the standard deviation of the amount of carbon fiber in a segment. To confirm the reliability of the model and the formula, we measured the standard deviation of the amount of carbon fiber in CFRTP specimens, showing that the trend for CFRTP specimens matched the estimated values.

DOI： 10.20965/ijat.2020.p0208

Effect of Mating Material and Graphitization on Wear of a-C:H Coating in Boundary Base Oil Lubrication Reviewed International journal

Kouami Auxence Melardot Aboua, Noritsugu Umehara, Hiroyuki Kousaka, Takayuki Tokoroyama, Motoyuki Murashima, Mohd Muhyiddin Bin Mustafa, Yutaka Mabuchi, Tsuyoshi Higuchi, Masahiro Kawaguchi

Tribology Letters Vol. 68 ( 1 ) page： 24 2020.1

Authorship：Last author Language：English Publishing type：Research paper (scientific journal)

Hydrogenated amorphous carbon (a-C:H) coating exhibits different wear behaviors depending on its counterpart material in boundary lubricated sliding contact. In previous works, tribological behaviors of a-C:H coating were investigated against steel, chromium, and germanium counterpart materials. The specific wear rate of a-C:H coating was found to decrease with the ability of its counterpart material to react with or dissolve carbon. The present study investigated how graphitization of a-C:H coating's top layers and interactions of the counterpart material with carbon influence wear behaviors of a-C:H coating in boundary lubrication. Results show that a-C:H coating shows graphitization of its top layers regardless the counterpart material. Correlation with differences in wear behaviors of the a-C:H coating leads to the conclusion that graphitization will induce high wear of a-C:H coating only when there are also atomic interactions between the DLC coating and its counterpart material.

DOI： 10.1007/s11249-019-1248-6

The tribological property of DLC under lubrication with GDOP and GDTP additives having glycerin and phosphate structure

EFFECTS OF LUBRICATION CONDITION ON FRICTION AND WEAR IN OIL LUBRICATION FOR ALUMINIUM ALLOY BEARINGS WITH VARIOUS CARBONACEOUS HARD COATINGS

Umehara Noritsugu, Kitamura Tomoki, Tokoroyama Takayuki, Murashima Motoyuki

7TH INTERNATIONAL CONFERENCE INTEGRITY-RELIABILITY-FAILURE (IRF2020) page： 1045 - 1046 2020

KANI Takumi, TOKOROYAMA Takayuki, UMEHARA Noritsugu, MURASHIMA Motoyuki, YAGISHITA Kazuhiro

The Proceedings of Mechanical Engineering Congress, Japan Vol. 2020 ( 0 ) page： S11311 2020

Language：Japanese Publisher：The Japan Society of Mechanical Engineers

In general, several mechanical parts are subjected to friction and wear. To prevent unfavorable wear and high friction coefficient, additives can work to reduce friction force, to build up thin film on the surfaces which is so-called tribofilm. Recently, Diamond-Like Carbon (DLC) is focused because it has excellent low friction and high wear proof as solid lubricant. However, several researchers already reported that ta-C showed abnormal wear when it rubbed with GMO that is a kind of additive, although it showed very low friction coefficient. To improve friction property, GDTP and GDOP was developed that has structure of GMO and dithio-phosphate functional group derived from ZnDTP which has high wear resistance. To clarify the effects of GDOP, we performed XPS analysis after the friction tests. In the friction tests, an a-C:H coating, and SUJ2 balls were used under boundary lubrication condition at 20, 50 and 80 ℃, and applying normal load was 1 N. Friction tests were conducted in PAO (Poly-α-olefin) oil, PAO with each GMO, GDTP and GDOP additives. In PAO with GDOP situation, the friction coefficient decreased down to 0.05. And the specific wear rate of SUJ2 ball was larger than with GMO and GDTP. The result of XPS analysis, although the binding energy of PO4 was observed, that of FePO4 was hardly observed. This suggests that when GDOP was added, the tribofilm that increased friction coefficient was not formed because PO4 and Fe hardly reacted. As a result, the wear of an SUJ2 ball was small volume.

DOI： 10.1299/jsmemecj.2020.s11311

"FRICTIONLESS" DIAMOND-LIKE COATINGS AND IN-SITU OBSERVATION USING REFLECTANCE SPECTROSCOPY

Umehara, N

7TH INTERNATIONAL CONFERENCE INTEGRITY-RELIABILITY-FAILURE (IRF2020) page： 7 - 8 2020

The Surface Enhanced Raman Scattering Analysis for Carbonaceous Coating by Using Au Nano-Particles Reviewed

Tokoroyama Takayuki, Murashima Motoyuki, Umehara Noritsugu

Tribology Online Vol. 15 ( 5 ) page： 300 - 308 2020

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In general, Raman analysis is one of the useful candidates to obtain structure of carbonaceous coatings. To improve the depth resolution of Raman analysis, surface-enhanced Raman Scattering (SERS) using gold nanoparticles (Au nanoparticles: AuNPs) and Au sputtered particles were investigated. The analysis was conducted to approximately 1.7, 2.4, 4.7, and 10.0 nm thickness of carbon coatings on silicon substrate with a 532 nm incident wavelength laser. The results indicated that the underlying silicon substrate was detected in the results of the Au sputtering method. Contrastingly, the underlying silicon substrate was not detected by the AuNPs method. This result clarified that using the AuNPs method, the detection depth of the carbon film was approximately 1.7 nm or less. The a-C:H coating was processed using a calotester, and SERS measurements at different depths were performed for the 633 and 532 nm wavelengths using the AuNPs method. As a result, the IG peak position tended to increase from the vicinity of the inter face between the a-C:H coating and the substrate to the surface. In addition, the ID/IG ratio was as low as 0.28 near the substrate and 0.72 at 3800 nm.

DOI： 10.2474/trol.15.300

Effect of doped tantalum in ta-CNx film or tantalum as counterpart material on the friction and wear properties of ta-CNx Reviewed

HOJO Koki, UMEHARA Noritsugu, TOKOROYAMA Takayuki, MURASHIMA Motoyuki

Transactions of the JSME (in Japanese) Vol. 86 ( 888 ) page： 20-00018 - 20-00018 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

In order to clarify the effect of Ta (tantalum) content on the friction and wear characteristics of the ta-CNx (tetrahedral amorphous carbon nitride) coating, an IBA-FAD (Ion Beam Assisted Filtered Arc Deposition method) was applied to generate hard carbonaceous coating to achieve low friction coefficient in ambient air. Following research works clarified that Ta containing carbon nitride (CNx:Ta) showed friction coefficient lower than 0.05 in ambient air, however, the coating only had around 10 GPa hardness which was assumed to be soft in industrial fields. To confirm Ta containing to the ta-CNx coating on friction and wear properties, ta-CNx:Ta coating was synthesized by IBA-FAD and an arc plasma gun which supplied different amount of Ta by using pulse discharge technique (100 or 200 pulse/min.). The hardness of ta-CNx was approximately 54 GPa, then the hardness of Ta containing ta-CNx became softer than ta-CNx such as approximately 33 GPa (ta-CNx:Ta200). After the ball-on-disk friction test between those coatings and SUJ2 disk, a specific wear rate of those coatings did not along with its hardness. From the XPS (x-ray photoelectron spectroscopy) analysis, oxygen/carbon ratio of the topmost coating surface decreased by containing Ta. Those results implied that Ta in the coating may have a possibility to prevent oxidation of carbonaceous coating. The friction coefficient of ta-CNx, ta-CNx:Ta100 and ta-CNx:Ta200 showed around 0.15 during friction test. To confirm the importance of Ta transformed layer on low friction property, friction test between ta-CNx coating and thin Ta coated SUJ2 disk was conducted. The friction coefficient of the pair became the lowest among them which value was approximately 0.08.

DOI： 10.1299/transjsme.20-00018

Preventing coagulated-blood adhesion on a coated electrosurgical knife Reviewed

TOKOROYAMA Takayuki, KOBAYASHI Masahiro, MURASHIMA Motoyuki, UMEHARA Noritsugu, OGAWA Koki, YOROZU Takayuki, UCHIDA Junichi

Transactions of the JSME (in Japanese) Vol. 86 ( 889 ) page： 20-00273 - 20-00273 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

In the past several decades, electro medical equipment has been developing to enhance surgical technologies. Using electro surgical knife is very common in everywhere of medical scene now a days. An electro surgical knife is consisted with power supply, metal tip and return electrode. In the case of using it to stop bleeding by coagulation mode, the tip surface is frequently covered by coagulated blood, then it is not able to discharge again. It means that the surgeons should replace it to new metal tip to continue surgical operation. In order to overcome this problem, some tips are covered by silicon type coating to prevent coagulated blood adhesion. However, it still has problems of continuous using, low heat invasiveness for human organs and how design such tip surface. In this study, three different type coating tips and a non-coated tip were prepared to compare temperature rising abilities and coagulated blood adhesion on the surface. As a result, fully surface coated types and blade’s edge uncovered type realized excellent prevention ability of blood coagulation adhesion onto surface. Especially for the side edge uncovered type, it exhibited low temperature rising ability after the temperature exceeded 100 degree C. This result indicated that side edge uncovered type is one of the suitable design to prevent exceed temperature rising.

DOI： 10.1299/transjsme.20-00273

In –situ analysis of two phase lubricant oil film with a reflectance spectroscopy Reviewed

YAMADA Takazumi, UMEHARA Noritsugu, TOKOROYAMA Takayuki, MURASHIMA Motoyuki, SATO Taku, OHARA Kenji, HANYUDA Kiyoshi

Transactions of the JSME (in Japanese) Vol. 86 ( 884 ) page： 19-00315 - 19-00315 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Two phase lubricant has attracted attention as a lubricating oil with little change in viscosity with temperature change. The two phase lubricant consist of the low and high viscosity base oils which are miscible at high temperature but not at lower temperature. For exmaple, Mineral or synthetic base oil are used as a low viscosity lubricant and PAG（polyalkylene glycol）. In the high temperature region, PAG dissolves into mineral or synthetic base oil and the viscosity reduction is relieved. However, the structure and frictional characteristics of the oil film at the sliding part have not been elucidated. In this paper, in-situ analysis of the oil film formed on the friction surface was carried out with a reflection spectroscopic film thickness meter. And, this paper clarified the influence of the oil film structure and oil film thickness of the two phase lubricant and its friction characteristics. As a result, it was suggested that the oil film of the two phase lubricant in the sliding part was a multilayer due to the adsorption layer of PAG. In addition the two phase lubricant showed a friction coefficient lower by about 0.03 to 0.07 at the experimental temperature compared to PAO, and it was clarified that a thick oil film was formed.

DOI： 10.1299/transjsme.19-00315

The micro-meter-sized plastic asperities by AC electric field for Poly-vinyl chloride solvent Reviewed

YAMADA Yusei, TOKOROYAMA Takayuki, MURASHIMA Motoyuki, UMEHARA Noritsugu

Transactions of the JSME (in Japanese) Vol. 86 ( 892 ) page： 20-00228 - 20-00228 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

In order to create an inexpensive micrometer-sized plastic asperities, a polyvinyl chloride solvent dissolved in acetone was prepared so that the solvent droplet was put on silicon substrate and placed between parallel plate electrodes (the gap was 5 mm). The effects of concentration, DC/AC and their combination voltage on the creation of micrometer-sized plastic asperities were clarified. As a result, asperities with a height of more than 10 μm were observed from a solvent concentration more than 2.51 mg/ml. It was found that the asperities height increased linearly from around 10 μm to 14 μm with the applied voltage of 0.1 kV to 2.0 kV between the parallel plate electrodes. The effect of DC or AC of 2.0 kV on asperities height and number per unit area were conducted, then the height of asperities decreased from 14 μm to 10 μm when frequency was applied to 11 Hz. To confirm the effect of applying AC voltage on motion of the solvent droplet, high-speed camera observation was carried out. It was revealed that the droplet oscillated by applied AC voltage between parallel plates. The dimensionless height of the droplet increased and reached a maximum at AC 11 Hz. Finally, to clarify the effect of the initial voltage application method on the formation of asperities, a voltage was applied between the parallel plate electrodes under the conditions of DC/AC and no voltage for an initial evaporation time of 3 min. By applying AC 11 Hz during solvent evaporation period, it was clarified that the asperities dispersed most on the surface, then variations in asperities height were reduced.

DOI： 10.1299/transjsme.20-00228

The development of nano-sized PM filtration for a diesel engine oil using coagulation by an alternating electric field Reviewed

TOKOROYAMA Takayuki, SHIBASAWA Hotaka, UMEHARA Noritsugu

Transactions of the JSME (in Japanese) Vol. 86 ( 884 ) page： 20-00016 - 20-00016 2020

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

In general, a diesel engine does not have ignition system and it can ignite by self-ignition. It has pros that engine manufactures can consist engine components less than normal gasoline engines. However, diesel engines emit more particle matter (PM) rather than normal gasoline engine, so that diesel engines should have diesel particulate filter (DPF) to accumulate them even if it is in not only a exhaust gas but also an engine oil region. In this study, the authors clarified the possibility of PM accumulation method by using an alternating electric field applying between a metal needle and a plate to coagulate them as large particles more than 0.8 μm. The important parameters were an electric field intensity, frequency and applying time. The FESEM observation results indicated that approximately 100 nm-sized particles coagulated to be a large particle. Then, EDS analysis revealed that the particle did not include conventional engine additives such as zinc, molybdenum and calcium. Those results clearly indicated that the alternative electric field method can accumulate nano-sized PM.

DOI： 10.1299/transjsme.20-00016

Intelligent tribological surfaces: from concept to realization using additive manufacturing Reviewed International journal

M. Murashima, S. Yoshino, M. Kawaguchi, N. Umehara

Int J Mech Mater Des Vol. 15 ( 4 ) page： 757 - 766 2019.12

Investigating running-in behavior to understand wear behavior of ta-C coating with filtered cathodic vacuum arc deposition Reviewed International coauthorship International journal

Woo-Young Lee, Takayuki Tokoroyama, Motoyuki Murashima, Noritsugu Umehara

JURNAL TRIBOLOGI Vol. 23 page： 38 - 47 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：MALAYSIAN TRIBOLOGY SOC-MYTRIBOS

In this study, to clarify running-in cycle and role of carbon transfer layer on wear, ta-C coatings were subjected to friction tests under 200 degrees C in air with a different sliding cycles. The steady state friction coefficient of 0.02 was obtained after finishing a running-in cycles approximately 2,000 cycles. During the steady state, wear rate of ta-C decreased with increasing number of cycles. Such the decrease of wear rate was explained by polished defects presented on surface and form carbon transfer layer on the counter-part material. The mechanism of those tribological properties was analyzed by Raman spectroscopy, scanning electron microscope observation and 3D measuring laser microscope.

Effect of Carbon Diffusion on Friction and Wear Behaviors of Diamond-Like Carbon Coating Against Germanium in Boundary Base Oil Lubrication Reviewed International coauthorship International journal

Kouami Auxence Melardot Aboua, Noritsugu Umehara, Hiroyuki Kousaka, Takayuki Tokoroyama, Motoyuki Murashima, Yutaka Mabuchi, Tsuyoshi Higuchi, Masahiro Kawaguchi

Tribology Letters Vol. 67 ( 2 ) page： 65 2019.6

Language：English Publishing type：Research paper (scientific journal)

Diamond-like carbon (DLC) coatings are designed to work under severe lubrication conditions. Depending on working environment, lubrication condition, and counterpart material, DLC coatings can exhibit crucial variations in their tribological behaviors. In the search of a counterpart material to improve tribological performances of DLC coatings in desired environment, we found out in previous work that carbon diffusion is an important parameter that influences the tribological behaviors of amorphous hydrogenated (a-C:H) coating in boundary lubrication. a-C:H coating exhibits high wear against steel counterpart material that has a high carbon affinity/solubility, while its exhibits lower wear against chromium counterpart material that has lower carbon affinity/solubility than steel. These recent findings imply that consideration of the carbon affinity/solubility when choosing a counterpart material for a-C:H coating in boundary lubrication might be of significant importance to improve tribological performances of a-C:H coating. This research investigates tribological behaviors of a-C:H coating against germanium counterpart material that has extremely low carbon affinity/solubility. Results show that there is no atomic interaction between a-C:H coating and germanium during friction and wear test, followed with a very low wear of a-C:H coating.

DOI： 10.1007/s11249-019-1179-2

The tribological potential of graphene growth from solid waste Reviewed International coauthorship

Noor Ayuma Mat Tahir, Fakulti Kejuruteraan Mekanikal, Mohd Fadzli Bin Abdollah*, Noreffendy Tamaldin, Hilmi Amiruddin, Mohd Rody Bin Mohamad Zin, Takayuki Tokoroyama and Noritsugu Umehara

Progress in Industrial Ecology – An International Journal Vol. 13 ( 4 ) page： 401 - 413 2019.4

Effect of oxygen on degradation of defects on ta-C coatings deposited by filtered arc deposition Reviewed International journal

Murashima Motoyuki, Deng Xingrui, Izuoka Hiroto, Umehara Noritsugu, Kousaka Hiroyuki

SURFACE & COATINGS TECHNOLOGY Vol. 362 page： 200 - 207 2019.3

Tribological properties of ta-CNx coating sliding against steel and sapphire in unlubricated condition Reviewed International journal

Xiaoxu Liu, Noritsugu Umehara, Takayuki Tokoroyama, Motoyuki Murashima

TRIBOLOGY INTERNATIONAL Vol. 131 page： 102 - 111 2019.3

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Tribo-behavior of tetrahedral amorphous carbon nitride (ta-CNx) coating in unlubricated condition was investigated in this study. Sliding against steel, low nitrogen content ta-CNx exhibits much lower friction and wear as temperature increases, with less adhesion wear than ta-C and remained relatively higher hardness (45.01 GPa). Nevertheless, against sapphire ta-C outperforms ta-CNx greatly, and graphitization could be found at 120 degrees C. With atmosphere humidity increasing, ta-CNx shows significantly decreased friction, implying the tribo-character of high sp(3) bonding structure. Meanwhile, dry air seems to be the harshest condition for ta-CNx, since O-2 in the atmosphere might lead to oxidized wear of ta-CNx even under room temperature. Furthermore, in humid N-2, as an inert gas with high humidity, ta-CNx shows the lowest friction and wear.

DOI： 10.1016/j.triboint.2018.10.022

Processing thin (<10 µm), dense, flexible α-Al2O3 films from nanopowders Reviewed International coauthorship International journal

TAKEUCHI Makoto, NIEDERMAIER Matthias, JANSOHN Monika, UMEHARA Noritsugu, LAINE Richard M.

Journal of the Ceramic Society of Japan Vol. 127 ( 2 ) page： 81 - 89 2019.2

Language：English Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan

Normally, it is very difficult to process thin ceramic films (<10 µm) except by vapor deposition methods. This is because in traditional ceramics processing, initial powder particle sizes (typical average particle sizes, APSs >200 nm) make it difficult to realize mechanically robust thin films after sintering to full density due to excessive grain growth. One solution to this problem is to start with nanopowders (APSs <100 nm). Here we present efforts to use simple, easily available nano δ-Al2O3 (transition or t-Al2O3) nanopowders (NPs) to process the subject films. Thus t-Al2O3 NPs when properly dispersed, doped with 0.5–5 wt.% MgO and ball milled with a polymeric binder provide castable systems. Wire wound roller drawing/tape casting provides access to thin green films (10–30 µm) with ≈75 wt.% ceramic loadings. Following binder burnout and careful sintering to temperatures of up to 1500°C/7 h/air but preferably slightly lesser conditions leads to dense ≤10 µm films with average α-Al2O3 grain sizes of 500–800 nm. At higher MgO concentrations, spinel phase separates during sintering likely inhibiting grain growth. These relatively dense films are flexible and translucent. Such films, because of their flexibility, may offer utility as catalyst supports, electronic substrates or as hard facings for other materials.

DOI： 10.2109/jcersj2.18099

The clarification of low friction mechanism in base oil lubrication of ta-CNx coating by in-situ observation with reflectance spectroscopy Reviewed

OKAMOTO Tatsuya, UMEHARA Noritsugu, TOKOROYAMA Takayuki, MURASHIMA Motoyuki

Transactions of the JSME (in Japanese) Vol. 85 ( 875 ) page： 19-00071 - 19-00071 2019

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Among DLC (Diamond-Like Carbon), ta-C (tetrahedral amorphous Carbon) coatings have been applied to improve fuel efficiency in automobile engines. Furthermore, it has been reported that a ta-CNx (tetrahedral amorphous Carbon Nitride) coating showed more than 50% lower friction coefficient in base oil lubrication compared to ta-C coating. On the other hand, the low friction mechanism of the ta-CNx coating has not been clarified. From the previous research, low friction mechanism of the ta-CNx coating in oil lubrication is considered that the increment of oil film thickness in accordance with increasing the oiliness of the transformed layer is important. However, the effects of oil film thickness and oiliness of the transformed layer on friction coefficient have not been quantitatively clarified, because oil film thickness and oiliness of the transformed layer have not been measured during friction. Therefore, in this research, the objective was set to clarify the low friction mechanism of the ta-CNx coating in oil lubrication by in-situ observation with reflectance spectroscopy, and oil film thickness and physical properties (polarizability, chemical bonding fraction) of the transformed layer was measured by in-situ observation with reflectance spectroscopy. Using in-situ observation with reflectance spectroscopy, film thickness, refractive index n and extinction coefficient k can be measured during friction test. And polarizability and chemical bonding fraction of the transformed layer were estimated from refractive index and extinction coefficient. From in-situ observation with reflectance spectroscopy, low friction mechanism of the ta-CNx coating in oil lubrication was proposed as shown below. The transformed layer was formed during friction and the polarizability of the transformed layer increased in accordance with decreasing C-Csp2 bonding fraction of the transformed layer, and PAO4 oil molecules were physically adsorbed on the transformed layer. As a result, oil film thickness increased and low friction occurred.

DOI： 10.1299/transjsme.19-00071

Effect of Pillar and Mesh Structure of Tetrahedral Amorphous Carbon (ta-C) Coatings on the Wear Properties and Fracture Toughness of the Coating Reviewed International coauthorship International journal

Bin Mustafa Mohd Muhyiddin, Umehara Noritsugu, Tokoroyama Takayuki, Murashima Motoyuki, Shibata Akinori, Utsumi Yoshiharu, Moriguchi Hideki

Tribology Online Vol. 14 ( 5 ) page： 388 - 397 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

Wear by fracture is among the factors associated with the DLC coating failures in the tribological application. The current study investigated the link between the wear and the fracture-toughness on the novel Pillar and Mesh structure ta-C coatings, in addition to conventional ta-C coatings. The tribological properties of these coatings were examined under base-oil lubrication via ball-on-disk tribo-tester and micro indentation technique was used to characterize the fracture toughness. The wear track and the indentation mark were analyzed using the optical microscope, 3D laser microscope and FE-SEM. The friction coefficient for ta-C, Pillar ta-C and Mesh ta-C are within the range of 0.071 to 0.106. Mesh ta-C indicated the highest wear resistance, followed by the Pillar ta-C and conventional ta-C. Also, Mesh ta-C demonstrated the highest fracture-toughness value with 16.6 MPa·m1/2, followed by Pillar ta-C with 13.4 MPa·m1/2 in contrast to ta-C. Greater resistance to wear for ta-C with Pillar and Mesh structure was detected with an increased fracture-toughness and improvement in crack propagation inhibition. Moreover, the Pillar and Mesh ta-C provides superior rate of crack-energy dissipation as compared to the ta-C.

DOI： 10.2474/trol.14.388

Investigating running-in behavior to understand wear behavior of ta-C coating with filtered cathodic vacuum arc deposition Reviewed International coauthorship International journal

Lee W.Y., Tokoroyama T., Murashima M., Umehara N.

Jurnal Tribologi Vol. 23 page： 38 - 47 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Jurnal Tribologi

In this study, to clarify running-in cycle and role of carbon transfer layer on wear, ta-C coatings were subjected to friction tests under 200 °C in air with a different sliding cycles. The steady state friction coefficient of 0.02 was obtained after finishing a running-in cycles approximately 2,000 cycles. During the steady state, wear rate of ta-C decreased with increasing number of cycles. Such the decrease of wear rate was explained by polished defects presented on surface and form carbon transfer layer on the counter-part material. The mechanism of those tribological properties was analyzed by Raman spectroscopy, scanning electron microscope observation and 3D measuring laser microscope.

The tribological potential of graphene growth from solid waste Reviewed International coauthorship International journal

Tahir N.A.M., Abdollah M.F.B., Tamaldin N., Amiruddin H., Zin M.R.B.M., Tokoroyama T., Umehara N.

Progress in Industrial Ecology Vol. 13 ( 4 ) page： 401 - 413 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Industrial Ecology

This study aimed to identify the tribological potential of graphene growth from solid waste products on copper substrate via the chemical vapour deposition method. The study focused on graphene growth from fruit cover plastic waste (FCPW) and oil palm fibre (OPF), the graphene structure was zexamined using Raman spectroscopy. Then, the tribological testing was performed using a ball-on-disc tribometer, and the hardness was performed using a nano-indenter on both the worn and unworn surfaces. The results show that graphene was successfully grown from both sources. Meanwhile, the tribological study found that both coatings showed a higher coefficient of friction (μ) compared to pure copper. However, the wear rate (k) was contradicted by the μ where the k was found to be 60% to 75% lower than pure copper. Finally, the hardness analysis revealed that the coating was damaged at 100 m sliding as the surface hardness increased.

DOI： 10.1504/PIE.2019.102864

Effect of Carbon Diffusion on Friction and Wear Behaviors of Diamond-Like Carbon Coating Against Cr-Plating in Boundary Base Oil Lubrication Reviewed International journal

Aboua Kouami Auxence Melardot, Umehara Noritsugu, Kousaka Hiroyuki, Tokoroyama Takayuki, Murashima Motoyuki, Mabuchi Yutaka, Higuchi Tsuyoshi, Kawaguchi Masahiro

Tribology Online Vol. 13 ( 5 ) page： 290 - 300 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

Investigations on tribological behaviors of Diamond-like Carbon (DLC) coating against other materials are strongly needed for scientific and industrial purposes. Recently, carbon diffusion has been found to play a key role in the wear of hydrogenated amorphous carbon (a-C:H) DLC coating when it is rubbed against steel counterpart material in boundary lubrication. Chromium has been reported to decrease carbon diffusion due to increase of the activation energy. In this research, we investigated on the effects of carbon diffusion on friction and wear properties of a-C:H coating when rubbed against Cr plating material. Results show that compared to steel counterpart, a-C:H coating exhibits lower friction coefficient, lower wear rate, and lower carbon diffusion rate when rubbed against Cr plating counterpart.

DOI： 10.2474/trol.13.290

The Clarification of Friction Mechanism in Oil Lubrication for CNx Coating by In-Situ Observation of Friction Area with Reflectance Spectroscopy Reviewed

OKAMOTO Tatsuya, UMEHARA Noritsugu, MURASHIMA Motoyuki, SAITO Koji, MANABE Kazuyoshi, HAYASHI Keiji

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 63 ( 11 ) page： 755 - 767 2018.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

To clarify the low friction mechanism of CNx coating in PAO oil lubrication, we measured reflectance spectrum at friction area in-situ by reflectance spectroscopy during friction test against a sapphire hemi-sphere pin in PAO oil. We observed and estimated thickness of PAO oil film, surface roughness of CNx coating, thicknesses and polarizability of transformed layer formed on bulk CNx coating during friction test by analyzing reflectance spectrum. We proposed that the decreasing of load ratio of boundary lubrication mode to total load is the one of governing factor to reduce friction on the basis of the increasing of Λ value. Also we proposed the increasing of adsorption of PAO oil to the CNx transformed layer is the second governing factor on the basis of the increasing of polarizability of PAO oil and transformed layer, that leads to the increasing of van der Waals force between transformed layer and PAO oil as low friction mechanism of CNx in PAO oil lubrication.

DOI： 10.18914/tribologist.17-00023

Deposition of ta-C:B Coating by FCVA Using Boron Doped Target and Its Tribological Behaviors at Elevated Temperature up to 300℃ Reviewed

Effect of ZnDTP Triboflim's Morphology on Friction Behaviors of DLC Coatings: Tribofilm Characterization by 3D Scanning Electron Microscope Observation Reviewed International coauthorship

K. A. M. Aboua, N. Umehara, H. Kousaka, T. Tokoroyama, M. Murashima, H. Abdullah Tasdemir, Y. Mabuchi, T. Higuchi

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 12 ( 7 ) 2018.11

NEMOTO Kouki, UMEHARA Noritsugu, TOKOROYAMA Takayuki, MURASHIMA Motoyuki, TAKIMOTO Yuji, NAKAMICHI Kenji

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 63 ( 10 ) page： 699 - 705 2018.10

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

Boron doped tetrahedral amorphous carbon (ta-C:B) coatings were deposited with Filtered Cathodic Vacuum Arc (FCVA) method using boron doped graphite target (B=0, 5 and 10 at. %). The material properties and tribological properties of ta-C:B coatings were obtained at 23~300℃. The amount of boron contents in ta-C:B coatings are from 0 to 5.1 at. %, and the hardness of coatings ware more than 30 GPa. The friction coefficient of ta-C:B3.1 at 300℃ is about 0.02 in air. The specific wear rate of ta-C:B coating were lower than normal ta-C coating by 34% and 46% for ta-C:B3.1 and ta-C:B5.1, respectively. The sp2/(sp2+ sp3) ratio measured by XPS and O/C ratio measured by AES increased through the friction at 300℃ for ta-C, on the other hand both values did not change for ta-C:B. Friction coefficients of ta-C:B3.1 were shown as 0.055 at 23℃ and about 0.02 at 100~300℃. The specific wear rate of ta-C:B3.1 at 23~300℃ in air was about 2.0 × 10−6 mm3/Nm. From these results, we confirmed that ta-C:B shows lower friction and higher specific wear resistance at 23~300℃ in air than ta-C.

DOI： 10.18914/tribologist.18-00003

CiNii Books

The effects of oil additives and mating materials to the friction, wear and seizure characteristics of a-C:H coating Reviewed International coauthorship International journal

Mohd Taufik bin Taib, Noritsugu Umehara, Takayuki Tokoroyama, Motoyuki Murashima

JURNAL TRIBOLOGI Vol. 18 page： 1 - 19 2018.9

Language：English Publishing type：Research paper (scientific journal) Publisher：MALAYSIAN TRIBOLOGY SOC-MYTRIBOS

In this study, friction and wear behaviour of amorphous hydrogenated carbon (a-C:H) DLC coating slide against SUJ2, TiC and TiN mating material disks in Base and ZnDTP+MoDTC oils boundary lubrication is comparatively investigated to determine the most favourable DLC/mating material/lubricant and interrelated tribofilm formation mechanism on each mating mating materials. Tribological tests were executed by utilizing roller on disk friction tester, nano-indentation hardness test, 3D optical surface profiler, and EDS-SEM were used to characterize the tribofilm formed on both worn roller and disk surfaces. The results showed that the wear volume of a-C:H/TiC tribo-pair in ZnDTP+MoDTC marked a tremendous wear volume reduction compared to than that of in Base oil. EDS investigation on tribofilm element investigation revealed that SUJ2 and TiN mating material disk attracted high concentration of Molybdenum at% on its surface that later caused high wear volume on both roller and disk sliding surfaces. TiC mating material disk however, formed a low at% yet helpful tribofilm consisting of a fraction of Zn phosphate from ZnDTP attached on both roller and disk which assisted the reduction of wear volume.

The Effect of UV Irradiation to a-C:H on Friction and Wear Properties under PAO Oil Lubrication Including MoDTC and ZnDTP Reviewed International journal

bin Taib Mohd Taufik, Umehara Noritsugu, Tokoroyama Takayuki, Murashima Motoyuki

Tribology Online Vol. 13 ( 3 ) page： 119 - 130 2018.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

One of the solutions to reduce friction between two sliding surfaces in automobile engine is by applying DLC coating to engine components. However, it is critical that the effect of lubricant additives to DLC coating to be clarified before hands as to avoid components failure. In this study, tribological friction test between SUJ2 balls and as-deposited plus UV irradiated a-C:H coatings was conducted to clarify the effect of ultraviolet irradiation to DLC coating in four different additives added lubricant oils. AFM, nano-indentation hardness test, ellipsometery, Zygo, and EDS-SEM were used to investigate the effect of UV irradiation to a-C:H DLC before and after friction test. Prior the friction test, the results showed that UV irradiation presented no significant change in terms of hardness and roughness but the irradiation did penetrate into topmost surface of the a-C:H coating to several degree and created dangling bonds available to interact with lubricant additives elements. Friction test results showed that UV irradiated a-C:H coatings presented lower friction coefficient than as deposited a-C:H coatings. Worn surface analysis revealed that UV irradiated a-C:H coatings attracted more lubricant additives element to attach on its surface thus created thicker tribofilm on its own surface and its counter materials, resulted in lower friction coefficient than the as-deposited a-C:H coatings.

DOI： 10.2474/trol.13.119

Chemical modification at and within nanopowders: Synthesis of core-shell Al2O3@TiON nanopowders via nitriding nano-(TiO2)(0.43)(Al2O3)(0.57) powders in NH3 Reviewed International coauthorship International journal

You Fei, Sun Kai, Yi Eongyu, Nakatani Eitaro, Umehara Noritsugu, Laine Richard M

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 101 ( 4 ) page： 1441 - 1452 2018.4

Effect of nanoparticles as lubricant additives on friction and wear behavior of tetrahedral amorphous carbon (ta-C) coating Reviewed

Li Xiang, Murashima Motoyuki, Umehara Noritsugu

JURNAL TRIBOLOGI Vol. 16 page： 15-29 2018.3

Effect of nanoparticles as lubricant additives on friction and wear behavior of tetrahedral amorphous carbon (ta-C) coating Reviewed International coauthorship International journal

Li Xiang, Murashima Motoyuki, Umehara Noritsugu

JURNAL TRIBOLOGI Vol. 16 page： 15-29 2018.3

Effect of Substrate Bias and Temperature on Friction and Wear Properties for ta-C Coating Prepared under Different Substrate Bias Voltages with Filtered Cathodic Vacuum Arc Deposition Reviewed International coauthorship International journal

Lee Woo-Young, Tokoroyama Takayuki, Jang Young-Jun, Umehara Noritsugu

Tribology Online Vol. 13 ( 5 ) page： 241 - 247 2018

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In this paper, the tribological behaviors of 1 μm of tetrahedral amorphous carbon (ta-C) coatings deposited with a different substrate bias of -0 V, -100 V and -300 V are examined under elevated temperature up to 600°C. It is found that wear behavior could be divided into two distinct regions according to testing temperature. The variation trend of the specific wear rate of ta-C coatings in region I at 23, 100 and 200°C are affected by abrasive particles which coincide with sp3 content of ta-C coatings. In region II at 300, 400 and 500°C, the transfer layer play a major role in reduction of wear rate as a function of substrate bias.

DOI： 10.2474/trol.13.241

Collecting micrometer-sized wear particles generated between DLC/DLC surfaces under boundary lubrication with an electric field

TOKOROYAMA Takayuki, KAMIYA Toru, AFMAD Nazeef Afifi Bin Hafiz, UMEHARA Noritsugu

Mechanical Engineering Letters Vol. 4 ( 0 ) page： 18-00089 - 18-00089 2018

Language：English Publisher：The Japan Society of Mechanical Engineers

Carbonaceous coatings such as Diamond-Like Carbon (DLC) are attractive candidates for reducing friction under boundary lubrication. However, the wear particles generated from the DLC are believed to form hard slurries that scratch surfaces like an abrasive, and they can shorten the lifetime of the DLC itself. Generally, in conventional automobiles, these wear particles are collected by oil filters. Modern engine bearings are required to reduce the friction coefficient to low levels so that low-viscosity lubricants are used to reduce resistance to flow. However, using a low-viscosity lubricant result in direct solid contact between surfaces, which disrupts the hydrodynamic lubrication and generates numerous wear particles. In this study, we carried out friction tests between DLC/DLC surfaces with kerosene as a boundary lubricant at room temperature. The friction tests were conducted over 12,000 cycles, and we replaced the lubricant after every 2000 cycles without changing the contact pair. Wear particles were collected from the lubricant using an electric field with the electrophoresis effect. The wear particles gathered near the positive electrode and fell onto a glass plate. Finally, after the kerosene evaporated, scanning electron microscope and laser optical microscope observations showed the relations between particle size and shape, the number of wear particles, and the friction coefficient.

DOI： 10.1299/mel.18-00089

Effect of ZnDTP triboflim's morphology on friction behaviors of DLC coatings: Tribofilm characterization by 3D scanning electron microscope observation Reviewed International journal

ABOUA Kouami Auxence Melardot, UMEHARA Noritsugu, KOUSAKA Hiroyuki, TOKOROYAMA Takayuki, MURASHIMA Motoyuki, TASDEMIR Haci Abdullah, MABUCHI Yutaka, HIGUCHI Tsuyoshi

Journal of Advanced Mechanical Design, Systems, and Manufacturing Vol. 12 ( 7 ) page： JAMDSM0129 - JAMDSM0129 2018

Language：English Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

ZnDTP antiwear additive for lubricating oil is known to absorb strongly on sliding surfaces in boundary lubricated tribosystems, forming a tribofilm, which is able to reduce the wear of involved surfaces. It is also known to increase the friction coefficient in most DLC/DLC contacts, with the exception of ta-C DLC / ta-C DLC contact, for which the difference in friction behaviors between a base oil + ZnDTP additive lubricated tribosystem and a base oil lubricated tribosystem is not very significant. In this study we investigate a characterization method of the shape of the tribofilm formed on different types of DLC coatings and on the relation between the shape of the tribofilm and the friction behavior of the related DLC coating. Results show that compared to other investigated DLC types, the tribofilm formed on ta-C DLC has some unique characteristic topography features that promote lower friction coefficient.

DOI： 10.1299/jamdsm.2018jamdsm0129

Comparative study on effects of load and sliding distance on amorphous hydrogenated carbon (a-C:H) coating and tetrahedral amorphous carbon (ta-C) coating under base-oil lubrication condition Reviewed

Xiang Li, Xingrui Deng, Hiroyuki Kousaka, Noritsugu Umehara

Wear Vol. 392 page： 84 - 92 2017.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

In this study, the lubricated friction and wear associated with diamond-like coatings (DLCs) of amorphous hydrogenated carbon (a-C:H) and hydrogen-free tetrahedral amorphous carbon (ta-C) were comparatively analyzed. The effects of load and sliding distance on the wear and friction behaviors of the coatings were studied under a boundary-lubrication condition using a poly-alpha-olefin base oil. The DLC-coated cylindrical specimens were slid with their central axes perpendicular to the sliding direction against a rotating steel counterface. The results show that the friction coefficient of the ta-C coating was lower than that of the a-C:H coating, though a graphitized layer was detected both inside and outside the wear scar of the a-C:H coating. Under a relatively low applied load (5 N), the specific wear rate of the ta-C coating was considerably lower than that of the a-C:H coating. When the load was increased to a critical value of 10 N, the specific wear rate of the ta-C coating increased rapidly to 3–5 times that of the a-C:H coating. However, the specific wear rate of the a-C:H coating decreased significantly when the load exceeded 10 N, which was consistently maintained thereafter. With the increase in the sliding distance, the specific wear rate of the ta-C coating increased rapidly. In comparison to the ta-C coating, the specific wear rate of the a-C:H coating decreased only slightly with the increase in the sliding distance
moreover, when the sliding distance exceeded 125 m, the specific wear rate of the a-C:H coating became much lower than that of the ta-C coating. The results of Raman spectroscopy, atomic force microscopy, and scanning electron microscopy show that the coatings were influenced by different types of wear mechanisms when slid under pure base-oil boundary-lubrication conditions.

DOI： 10.1016/j.wear.2017.09.009

Effect of oil temperature and counterpart material on the wear mechanism of ta-CNx coating under base oil lubrication Reviewed

Effect of mating materials on wear properties of amorphous hydrogenated carbon (a-C:H) coating and tetrahedral amorphous carbon (ta-C) coating in base oil boundary lubrication condition Reviewed International journal

Li Xiang, Sawaki Toshiya, Kousaka Hiroyuki, Murashima Motoyuki, Umehara Noritsugu

JURNAL TRIBOLOGI Vol. 15 page： 1-20 2017.12

Xiaoxu Liu, Ryo Yamaguchi, Noritsugu Umehara, Motoyuki Murashima, Takayuki Tokoroyama

WEAR Vol. 390-391 page： 312 - 321 2017.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE SA

Tetrahedral amorphous carbon nitride (ta-CNx), as an emerging and promising diamond-like carbon (DLC), has better mechanical properties than amorphous carbon nitride (a-CNx) to ensure the sufficient durability, and overcomes the limit of high internal stress of tetrahedral amorphous carbon (ta-C), which makes ta-CNx coatings of great worth of research for the tribological and mechanical applications. In this study, we present the effects of oil temperature and counterpart material on the wear behavior of ta-CNx coatings under base-oil lubrication, and further clarify the wear mechanism. ta-C and ta-CNx coatings with N/C atomic ratio of 2.2% and 11.0% were deposited by an ion beam assisted filtered arc deposition (IBA-FAD) system, and the tribological tests were performed using a ball-on-disk tribo-tester with ta-C and ta-CNx coated steel ball sliding against uncoated disk under base-oil lubrication. The results show that nitrogen doping tends to decrease the hardness and Young's modulus by reducing the sp(3) structure. Sliding against steel disk, with increase of sliding distance ta-CNx shows obviously distinct wear behavior compared to ta-C, much more slowly increasing wear volume, exhibiting excellent wear resistance. Increasing oil temperature from room temperature to 120 degrees C results in rising wear rates of all the three coatings, with totally worn out ta-C and much lower wear rate of ta-CNx, which decreases by more than half than ta-C for high nitrogen content ta-CNx. However, as the counterpart material changed from steel to alumina, the wear rate presents oppositely increasing tendency with N/C ratio, probably caused by the change of deciding factor to hardness in this mechanical wear. It is found that the wear performance of ta-CNx coating has a clear dependence on the oil temperature and counterpart material. Based on the results, the better wear resistance of softer ta-CNx against steel could be attributed to the less tribo-chemical wear between carbon and iron, due to the nitrogen doping partial passivation effect.

DOI： 10.1016/j.wear.2017.08.012

Effect of carbon diffusion on friction and wear properties of diamond-like carbon in boundary base oil lubrication Reviewed International journal

Kouami Auxence Melardot Aboua, Noritsugu Umehara, Hiroyuki Kousaka, Xingrui Deng, Haci Abdullah Tasdemir, Yutaka Mabuchi, Tsuyoshi Higuchi, Masahiro Kawaguchi

Tribology International Vol. 113 page： 389 - 398 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

In order to control wear and friction in industry, Diamond like carbon (DLC) hard coatings are widely applied in recent years due to their well appreciated mechanical and tribological properties. However, those properties are not yet well understood, as well as behavior of DLC hard coatings when rubbed against other materials. Other researchers reported that DLC hard coatings film show high wear when rubbed against steel counterpart and their durability decrease with the increase of the temperature. In this research, we investigated on friction and wear properties of DLC coatings and the results reveal that carbon diffusion has a key role in the wear and friction behavior of DLC coatings when rubbed against steel.

DOI： 10.1016/j.triboint.2016.10.047

Clarification of effect of transformed layer and oil film on low friction coefficient of CNx coating in PAO oil lubrication by in-situ observation of friction area with reflectance spectroscopy Reviewed

Hidenori Nishimura, Noritsugu Umehara, Hiroyuki Kousaka, Motoyuki Murashima

TRIBOLOGY INTERNATIONAL Vol. 113 page： 383 - 388 2017.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

In order to clarify a low friction mechanism of CNx (Carbon Nitride) coating in PAO (Poly Alpha Olefin) oil lubrication, we measured reflectance spectrum at friction area in-situ by reflectance spectroscopy. And we obtained thicknesses and polarizabilities of oil film and transformed layer formed on bulk CNx coating during friction test by analyzing reflectance spectrum. From results, we concluded that the increments of polarizabilities of transformed layer and oil film had an effect on increasing thickness of oil film, and then the lubricated condition changed from boundary to mixed lubrication. Finally CNx coating showed low friction coefficient in PAO oil lubrication.

DOI： 10.1016/j.triboint.2016.10.029

The effects of temperature, pressure and dissolved oxygen concentration (DO) in water on the wear of the hydrogenated diamond-like carbon (HDLC) at high temperature and pressurized water Reviewed

Mohd Rody Bin Mohamad Zin, Yuji Yagi, Keiji Sasaki, Naruhiko Inayoshi, Takayuki Tokoroyama, Noritsugu Umehara, Hiroyuki Kousaka, Shingo Kawara

Tribology International Vol. 109 page： 48 - 57 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

The aim of this study is to clarify the wear mechanism of hydrogenated diamond-like carbon (HDLC) coating in high temperature and pressurized water. A new reciprocating autoclave wear tester was developed to conduct the wear test between DLC coated pins against SUS316 plate in high temperature and pressurized water. The results showed that the wear of HDLC in water was greatly influenced by water temperature from 23 °C to 300 °C and dissolved oxygen concentration (DO) from 0.73 mg O/L to 47.5 mg O/L (mg O/L:milligrams oxygen per liter) in water. On the other hand, water pressure in the chamber did not have significant effect on the wear of HDLC when pressure was increased from 10 MPa to 30 MPa at 300 °C. Based on surface analysis by XPS, AFM nano scratch, Raman spectroscopy, and AES on the top most surface of the wear scar of HDLC, softening and oxidation of top layer of wear scar of HDLC was found to be the mechanisms of high wear of HDLC in high temperature and pressurized water. The transformation of sp3 to sp2 at higher water temperature is believed to be responsible for the reduced hardness of the top most surface of HDLC. Oxidation also provided softening of top layer of HDLC at higher DO in water.

DOI： 10.1016/j.triboint.2016.12.010

Microscopic origin of ultra-low friction coefficient between the wear track formed on carbon nitride coating and transfer layer on sliding ball in friction tests under dry N-2

Inoue Hiroshi, Muto Shunsuke, Arai Shigeo, Wasada Hiroaki, Umehara Noritsugu

SURFACE & COATINGS TECHNOLOGY Vol. 313 page： 31 - 39 2017.3

Language：Japanese Publisher：Surface and Coatings Technology

Carbon nitride (CNx) coatings have been found to exhibit an ultra-low friction coefficient (less than 0.01) after repeated sliding against a silicon nitride (Si3N4) ball in a dry nitrogen gas (N2) atmosphere. However, the mechanism for this has not yet been fully elucidated with respect to analyzing changes in the space structure of CNx. In the present study, we examined the microscopic structural changes in the near-surface structural transition layers of the wear track in the CNx coating and the transfer layer of the Si3N4 ball, using scanning transmission electron microscopy and electron energy-loss spectroscopy. We investigated the nitrogen concentration, density, and curvature of fragmented graphitic planes in the structural transition layers of both the CNx coating and the transfer layer of the Si3N4 ball by analyzing the plasmon peak and carbon K-edge. In addition, we theoretically examined the chemical bonding states of nitrogen doping in various model clusters using an ab initio molecular orbital method to clarify the role of nitrogen in the ultra-low friction behavior. The mechanism behind the ultra-low friction behavior is explained by nano-graphitization of the fragmented carbon structure with optimal nitrogen concentration passivating the contacting counter surfaces of the coating and ball formed during sliding.

DOI： 10.1016/j.surfcoat.2017.01.048

Tribological properties of ta-CNx coatings with different nitrogen content under oil lubrication conditions Reviewed

Effect of Electric Field on Adhesion of Thermoplastic Resin against Steel Plate, Reviewed

M. Murashima, N. Umehara, H. Kousaka, X. Deng

Tribology Online Vol. 12 ( 2 ) page： 42-48 2017.2

Microscopic origin of ultra-low friction coefficient between the wear track formed on carbon nitride coating and transfer layer on sliding ball in friction tests under dry N2. Reviewed International journal

H. Inoue, S. Muto, S. Arai, H. Wasada, N. Umehara

Surface Coatings & Technology Vol. 313 page： 31-39 2017.2

Effects of Ceramic Counterpart Material on Wear Property of a-C:H Coating under Reviewed

T. Yamanouchi, X. Deng, Y. Tanaka, N. Umehara, H. Kousaka

Tribologist Vol. 62 ( 1 ) page： 52-58 2017.1

H. Nishimura, N. Umehara, H. Kousaka, M. Murashima

Tribology International Vol. 113 page： 383-388 2017.1

Depth Profile of Oxygen of Diamond-Like Carbon Sliding Under Pressurized Hot Water Reviewed

M. R. B. Mohamad Zin, K. Okuno, N. Umehara, N. Inayoshi, K. Sasaki, S. Kawara,H. Kousaka

Tribology Online Vol. 12 ( 1 ) page： 8-17 2017.1

Deng Xingrui, Hattori Takafumi, Umehara Noritsugu, Kousaka Hiroyuki, Manabe Kazuyoshi, Hayashi Keiji

THIN SOLID FILMS Vol. 621 page： 12 - 18 2017.1

Language：English Publisher：Thin Solid Films

Carbon nitride (CNx) coatings exhibit a wide range of attractive properties that make them suitable for demanding mechanical and tribological applications. In this study, an ion beam assisted filtered arc deposition (IBA-FAD) method has been developed for the deposition of tetrahedral amorphous carbon nitride (ta-CNx) coatings. The ta-CNx coatings with various nitrogen contents were deposited by controlling the nitrogen flow to investigate the effects of nitrogen content on their tribological behavior. The composition and structure of the ta-CNx coatings were evaluated using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The tribological properties were examined using a ball-on-disk tribo-tester under oil lubrication condition. The results showed that nitrogen contents of ta-CNx coatings were restricted to the range of 0–11 at.% by nitrogen ion density. The hardness decreased with an increase in the nitrogen content as nitrogen decreased the fraction of sp3 carbon in the coatings. The ta-CNx coatings exhibit low friction under oil lubrication and the maximum value was obtained for samples containing 8 at.% of nitrogen. ta-CNx with 8–11 at.% of nitrogen exhibited markedly low wear rate.

DOI： 10.1016/j.tsf.2016.11.025

Clarification of high wear resistance mechanism of ta-CNx coating under poly alpha-olefin (PAO) lubrication Reviewed

Tribological properties of ta-CNx coatings with different nitrogen content under oil lubrication conditions Reviewed International journal

X. Deng, T. Hattori, N. Umehara, H. Kousaka, K. Manabe, K. Hayashi

Thin Solid Films Vol. 616 page： 134-140 2017.1

Xiaoxu Liu, Ryo Yamaguchi, Noritsugu Umehara, Xingrui Deng, Hiroyuki Kousaka, Motoyuki Murashima

TRIBOLOGY INTERNATIONAL Vol. 105 page： 193 - 200 2017.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Tetrahedral amorphous carbon nitride (ta-CNx) is suitable for tribological application due to its excellent mechanical and adhesion properties. In this study, ta-CNx coatings with N/C ratios (0-11%) are deposited by ion beam assisted filtered arc deposition (IBA-FAD), and the tribological properties are investigated with a ball on-disk tribo-tester. The results show that nitrogen doping decreases the fraction of sp(3) bonding, hardness, Young's modulus and roughness. In oil ta-CNx presents slightly decreasing friction coefficient and improving wear resistance with the N/C ratio, indicating softer ta-CNx with better wear resistance. The lower surface roughness after friction of high nitrogen content ta-CNx makes it more likely to transit to mixed lubrication, resulting in lower contact load that can explain the better wear resistance.

DOI： 10.1016/j.triboint.2016.10.016

Fabrication of Thin Solid Coating and Tribology with Plasma and Ion Beam Process

Future of Tribology and Technology Education with Tribology

UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 62 ( 10 ) page： 609 - 609 2017

KOUSAKA Hiroyuki, UMEHARA Noritsugu

Journal of the Japan Society for Precision Engineering Vol. 83 ( 4 ) page： 319 - 324 2017

Effect of drill surface texturing on back burr height with solid lubricating sheet in titanium alloy drilling Reviewed

OYAMA Shintaro, UMEHARA Noritsugu, KOUSAKA Hiroyuki, DENG Xingrui, MURASHIMA Motoyuki, HORIE Shigeru, MATSUYAMA Yousuke

Transactions of the JSME (in Japanese) Vol. 83 ( 849 ) page： 16-00378 - 16-00378 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

This paper describes about the effect of drill surface texturing on height of back burr in titanium alloy drilling process with solid lubricating sheet. Titanium alloy is difficult to conduct drilling because titanium alloy is hard and ductile material. And the workers cannot use plenty of liquid coolant for preventing the productivity decline when the work places are above their heads in production fields. Therefore drills are exchanged frequently even though the cost increases. In this study, we measured the cutting force by a loadcell to know the effect of drill surface texturing and solid lubricating sheet on drilling process of work pieces made of Ti-6Al-4V. As the results, drill with rough textured rake surface showed high burr height in exit of Ti-6Al-4V. On the other hand, drill with rough textured flank surface showed low burr height only if drilling with solid lubricating sheet. Moreover, drill with the specific texturing on flank surface by wire electric discharge machining showed low burr height.

DOI： 10.1299/transjsme.16-00378

Analysis of Wear Track on DLC Coatings after Sliding with MoDTC-Containing Lubricants Reviewed International journal

Ohara Kenji, Hanyuda Kiyoshi, Kawamura Yasushi, Omura Kentaro, Kameda Imari, Umehara Noritsugu, Kousaka Hiroyuki

TRIBOLOGY ONLINE Vol. 12 ( 3 ) page： 110-116 - 116 2017

Friction and Wear Properties of Tetrahedral Si-Containing Hydrogenated Diamond-Like Carbon Coating under Lubricated Condition with Engine-Oil Containing ZnDTP and MoDTC Reviewed International journal

Komori Kentaro, Umehara Noritsugu

Tribology Online Vol. 12 ( 3 ) page： 123 - 134 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

In this study, we investigated tribological properties of “tetrahedral” Si-containing hydrogenated DLC coating (TMS coating) during sliding against steel or cast-iron lubricated with engine-oil containing MoDTC and ZnDTP additives. TMS coatings derived from only tetramethylsilane were prepared using PACVD with high-bias process. TMS coating had the highly carbon sp3 bonded structure induced by Si (over 20 at.%) with high hydrogen content (30 at.%). TOF-SIMS analysis showed that TMS coating could form the additive-derived tribofilm on both of the non-ferrous coating surface and the ferrous counter surface to promote Mo-sulfide formation effectively, leading a low friction coefficient. The tribo-chemical reactions were related not only to Mo-sulfides formation, but also reduction of Mo-oxides. Mo-oxides could react with DLC material and induce hydrogen evolution and transformation into further weak carbon structure, causing an increasing wear of hydrogenated DLCs. TMS coating showed no significant wear in spite of plenty hydrogen content. Si induced sp3 bond and could act so as not to induce clustering of the sp2 phase. This could inhibit increasing wear of the DLC in the presence of MoDTC. The effectiveness of TMS coating in friction and wear behavior was shown to depend on tribo-chemical reactions and transformation of carbon bond structure.

DOI： 10.2474/trol.12.123

Proposal of lightweight and low starting torque slide bearing with looped carbon fibers brush Reviewed

SHITAKA Takuya, MURASHIMA Motoyuki, UMEHARA Noritsugu, TSUKIYAMA Yosuke, NITTA Isami, KOUSAKA Hiroyuki, DENG Xingrui

Transactions of the JSME (in Japanese) Vol. 83 ( 854 ) page： 17-00252 - 17-00252 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

This paper addresses a novel lightweight and low starting torque bearing with looped carbon fiber brush (LCFB). LCFB simulates bristle of living being. Moreover, the static friction coefficient is nearly equal to the kinetic friction coefficient. By applying LCFB to a slide bearings, where a shaft is supported by multiple LCFBs, it is realized low starting torque bearings as well as lightness compared to conventional ball bearings. In this paper, we manufacture prototype LCFB slide bearings. With the bearings, we compare friction torque between LCFB slide bearings, slide bearings and deep groove ball bearings. As results, the ratio of starting torque to regular torque of LCFB slide bearing is from 0.93 to 1.07 which is smaller than that of the slide bearing. When micro-spline shaft is used as a mating material of LCFB slide bearing, the torque reduces because of decrease of real contact area between LCFB and mating materials. In addition, since LCFB utilize elastic deformation of fibers, LCFB slide bearings are not endurable in heavy radial load as high as load rating of ball bearing. Therefore, we define the load capacity of LCFB slide bearing from buckling load of a carbon fiber bundle to avoid overload state. We propose the load capacity as a design guideline of LCFB slide bearings.

DOI： 10.1299/transjsme.17-00252

Depth Profile of Oxygen of Diamond-Like Carbon Sliding under Pressurized Hot Water Reviewed International coauthorship International journal

Bin Mohamad Zin Mohd Rody, Okuno Kiichi, Sasaki Keiji, Inayoshi Naruhiko, Umehara Noritsugu, Kousaka Hiroyuki, Kawara Shingo

Tribology Online Vol. 12 ( 1 ) page： 8 - 17 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

The wear mechanism of diamond-like carbon (DLC) in hot, pressurized water has been studied by the oxygen depth profile of DLC films pre and post a sliding test. The sliding test between DLC films coated on chromium molybdenum steel (JIS SCM420) pins and austenitic stainless steel (JIS SUS316) plates was conducted in a water environment by using high temperatures of 100, 200, 250 and 300°C and a high-pressured (10 MPa) autoclave friction tester. The dissolved oxygen concentration (DO) was 0.52 mg/L for oxygen-poor water and 40 mg/L for oxygen-rich water. The experimental results showed that the specific wear rate of DLC was strongly related to the water temperature and the DO concentration. The specific wear rate in both cases of oxygen-poor and oxygen-rich water showed a temperature dependency. When the temperature was below 200°C, the specific wear rate of DLC did not depend on the DO concentration. On the other hand, when the water temperature was more than 200°C, the specific wear rate drastically increased with the DO concentration. In order to prove the effect of oxidation on the wear rate of DLC, the depth profile of the oxygen concentration was compared to that of the carbon concentration on the inside and outside of the wear scar of DLC after sliding tests in hot, pressurized water. When the concentration of DO in the water was low at 0.52 mg/L, the O/C ratio was not affected by the water temperature. On the other hand, when the concentration of DO in water was high at 40 mg/L, the O/C ratio of the top surface increased from 0.05 to 0.18 with an increase in the water temperature on the inside of the wear scar of DLC, where the O/C ratio on the inside of the wear scar was higher than that on the outside of the scar. On the basis of the estimated rate of reaction between DLC and oxygen, determined from a linear relationship between ln (Oxidation wear volume) and the inverse temperature, it was concluded that the oxidation of DLC governed the wear of DLC in hot, pressurized water. Friction was found to enhance the oxidation wear of DLC from the estimated activation energy.

DOI： 10.2474/trol.12.8

Effect of Electric Field on Adhesion of Thermoplastic Resin against Steel Plate Reviewed International journal

Murashima Motoyuki, Umehara Noritsugu, Kousaka Hiroyuki, Deng Xingrui

Tribology Online Vol. 12 ( 2 ) page： 42 - 48 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Society of Tribologists

This work shows new method which controls adhesion strength between acrylic resin and metal mold with electric field. Usage of electric field is considered as a new solution to control adhesion of thermoplastic resin in Carbon-Fiber-Reinforced ThermoPlastic (thermoplastic CFRP) stamping process because this method can prevent CFRP from its degradation. In this work, we establish new adhesion tester which can apply Direct Current (DC) or Alternating Current (AC) field on metal specimens. In the results, when DC −12 V/mm is imposed on metal specimens, adhesion strength increases to 0.81 MPa which is 57% higher than that of no field condition. Negative component of surface energy after imposing DC −12 V/mm on metal specimens is 7.6 mJ/m2. This value is 56% smaller than that of no field condition. When AC electric fields is imposed, adhesion strength decreases from no electric field condition. The most effective AC field condition is AC 10 V/mm with 1 MHz, in which case adhesion strength is 0.29 MPa. This value is 44% lower than that of no field condition.

DOI： 10.2474/trol.12.42

Development of radio knife tip to prevent adhesion of coagulated blood by separate type thermosyphon Reviewed

TOKOROYAMA Takayuki, OSUKA Misato, UMEHARA Noritsugu

Transactions of the JSME (in Japanese) Vol. 83 ( 845 ) page： 16-00123 - 16-00123 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers

Radio knives are common tools in surgery. The adhesion of the tip of a radio knife to the human body through the coagulation of blood is a severe problem. A solution to this problem, suggested by other authors, is to cool the tip of the radio knife. However, introducing a cooling system, such as circulating water inside the tip with a pump, requires additional wires and pipes and may also distract the surgeons. To overcome these issues, we consider the possibility of embedding a separate type thermosyphon to cool the radio knife tip without any additional wires and pipes. The important parameters are the tip length, tip diameter, inner tip diameter, enclosure ratio of the working fluid, and grip length. First, to clarify the heat-transport possibilities, the top of the tip of a separate type thermosyphon radio knife was heated by a ceramic heater; this was done to measure the temperature difference between the radio knife tip surface and a heat release part. Second, suitable values for the tip length, diameter and other important parameters were considered. It was concluded that the highest cooling efficiency is obtained when the heating area is limited between 200 and 250 mm2 of the knife tip surface area. The inner pipe was indispensable to transport generated heat from the tip to the radio knife end. Consequently, it was revealed that the effective diameter of inner pipe was 0.48 mm in this research. To simulate the conventional surgery situations, the radio knife tip was immersed to blood and applied voltage to generate heat at the tip. It demonstrated 45.9 degree C at the maximum temperature while it was activated. Furthermore, the coagulation at the peripheral of the tip was observed, accordingly, the separate type thermosyphon radio knife exhibited a stop bleeding ability.

DOI： 10.1299/transjsme.16-00123

In-Situ Observation Apparatus for Structure Change of Topmost Layer of Cabonaceous Hard Coatings during Sliding with Refrectance Spectroscopty

NISHIMURA Hidenori, KOUSAKA Hiroyuki, UMEHARA Noritsugu

JOURNAL OF JAPANESE SOCIETY OF TRIBOLOGISTS Vol. 62 ( 7 ) page： 461 - 464 2017

Effects of ceramic counterpart material on wear property of a-C:H coating under various temperatures Reviewed

Yamanouchi T., Xingrui D., Tanaka Y., Umehara N., Kousaka H.

Toraibarojisuto/Journal of Japanese Society of Tribologists Vol. 62 ( 1 ) page： 52 - 58 2017

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Toraibarojisuto/Journal of Japanese Society of Tribologists

Carbon coatings have a keen attention according to its low friction, high hardness and high wear resistance properties. There are needs to apply carbon coatings into ceramic mechanical parts, such as mechanical seal. However the tribological properties of carbon coatings when slid against ceramics are still not investigated sufficiently. Generally tribological behaviors are affected by a counterpart material. Therefore more fundamental researches about counterpart material are necessary. In this research tribological behaviors of carbon coating when slid against various counterpart material, including SiC, SiC(O) that is SiC after annealing at 1000°C, Si3N4, Al2O3, Al2O3(Si) that includes more Si atomic concentration than Al2O3and Si wafer at various temperatures in air have been investigated. Carbon coating when slid against SiC showed the lowest wear rate at 23°C, and carbon coating when slid against Si3N4showed the lowest wear rate at 140°C and carbon coating when slid against SiC(O) showed the lowest friction coefficient at all temperature.