Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Country：Japan

Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

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

Scopus

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

<p>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.</p>

DOI： 10.18914/tribologist.23-00021

CiNii Research

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

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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

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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

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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

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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

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

DOI： 10.1007/s40430-024-04743-y

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

DOI： 10.1007/s11249-024-01829-5

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

DOI： 10.3389/fmech.2024.1371948

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

DOI： 10.1016/j.surfcoat.2024.130388

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Scopus

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

DOI： 10.26502/jsr.10020340

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

DOI： 10.1016/j.surfin.2023.103695

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

<p>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.</p>

DOI： 10.1299/jamdsm.2024jamdsm0032

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CiNii Research

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

<p>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.</p>

DOI： 10.2474/trol.18.292

CiNii Research

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

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

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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

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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

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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.

Scopus

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

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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

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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

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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

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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

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

DOI： 10.1016/j.triboint.2022.107938

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

DOI： 10.1016/j.triboint.2022.107956

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Scopus

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (other academic)   Publisher：Japanese Society of Tribologists  

DOI： 10.18914/tribologist.67.12_813

CiNii Research

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

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

DOI： 10.1007/s40544-021-0572-7

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

DOI： 10.1016/j.triboint.2021.107306

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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

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

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

<p>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.</p>

DOI： 10.18914/tribologist.22-00001

CiNii Research

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

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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

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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

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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

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

<p>Carbonaceous hard coatings have promising tribological properties, such as low friction, high hardness and high wear resistance. In particular, CN<i>_x</i>(Carbon Nitride) coating and a-C:H (hydrogenated amorphous carbon) coating show ultra low friction coefficient (<i>µ < </i>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.</p>

DOI： 10.18914/tribologist.21-00018

CiNii Research

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

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

Scopus

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

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

DOI： 10.1016/j.ceramint.2021.05.292

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Scopus

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

<p>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.</p>

DOI： 10.18914/tribologist.21-00001

CiNii Research

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

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Scopus

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

<p>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.</p>

DOI： 10.18914/tribologist.20-00020

CiNii Research

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

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

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

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

<p>To clarify the low friction mechanism of CN<i>_x</i> coating in PAO oil lubrication, we measured reflectance spectrum at friction area <i>in-situ </i>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 CN<i>_x</i> coating, thicknesses, and polarizability of the transformed layer formed on bulk CN<i>_x</i> 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 <i>Λ</i> value. Also we proposed the increasing of adsorption of PAO oil to the CN<i>_x</i> 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 CN<i>_x</i> in PAO oil lubrication.</p>

DOI： 10.2474/trol.16.49

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Scopus

CiNii Research

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

<p>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.</p>

DOI： 10.2474/trol.16.255

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Scopus

CiNii Research

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

<p>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.</p>

DOI： 10.2474/trol.16.263

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CiNii Research

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

DOI： 10.1016/j.triboint.2020.106565

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Scopus

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

DOI： 10.18914/tribologist.65.11_684

CiNii Research

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

DOI： https://doi.org/10.1299/transjsme.20-00228

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Precision Engineering  

DOI： 10.2493/jjspe.86.662

CiNii Research

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Surface Finishing Society of Japan  

DOI： 10.4139/sfj.71.547

CiNii Research

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

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

<p>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.</p>

DOI： 10.11420/jsat.64.428

CiNii Books

CiNii Research

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

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

DOI： 10.1016/j.tribint.2020.106565

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

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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

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Scopus

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

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

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

<p>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 20^thcentury, 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.</p>

DOI： 10.18914/tribologist.65.04_236

CiNii Research

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

<p>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, <i>S</i>_a, 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 <i>S</i>_ZJI<i>S</i>= 75 nm and <i>S</i>_a= 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 <i>S</i>_ZJIN= 25 nm and <i>R</i>_a= 0.43 nm, which were 86% lower than and similar to those of the non-polished ta-C surface, respectively.</p>

DOI： 10.20965/ijat.2020.p0190

Scopus

CiNii Research

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： doi.org/10.1299/transjsme.19-00315

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

DOI： doi.org/10.1299/transjsme.20-00016

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

<p>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.</p>

DOI： 10.20965/ijat.2020.p0208

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CiNii Research

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

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Scopus

Language：Japanese  

Web of Science

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>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.</p>

DOI： 10.1299/jsmemecj.2020.s11311

CiNii Research

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

<p>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 <i>I</i>_G<i> </i>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 <i>I</i><i>_D</i><i>/I</i>_G ratio was as low as 0.28 near the substrate and 0.72 at 3800 nm.</p>

DOI： 10.2474/trol.15.300

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CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.20-00018

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.20-00273

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.20-00228

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.20-00016

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.19-00315

CiNii Research

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

DOI： 10.1007/s10999-018-9435-4

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Scopus

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.

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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

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

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

DOI： 10.1016/j.surfcoat.2019.01.115

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Scopus

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

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Scopus

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

<p>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 <i>t</i>-Al₂O₃) nanopowders (NPs) to process the subject films. Thus <i>t</i>-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 <i>thin green films</i> (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.</p>

DOI： 10.2109/jcersj2.18099

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CiNii Research

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

<p>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 <i>n</i> and extinction coefficient <i>k</i> 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.</p>

DOI： 10.1299/transjsme.19-00071

CiNii Research

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

<p>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·m^1/2, followed by Pillar ta-C with 13.4 MPa·m^1/2 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.</p>

DOI： 10.2474/trol.14.388

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CiNii Research

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

Scopus

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.

Scopus

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

<p>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.</p>

DOI： 10.2474/trol.13.290

Scopus

CiNii Research

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

<p>To clarify the low friction mechanism of CN<i>x </i>coating in PAO oil lubrication, we measured reflectance spectrum at friction area <i>in-situ </i>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 CN<i>x </i>coating, thicknesses and polarizability of transformed layer formed on bulk CN<i>x </i>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 CN<i>x </i>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 CN<i>x </i>in PAO oil lubrication.</p>

DOI： 10.18914/tribologist.17-00023

CiNii Research

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

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

<p>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:B_3.1 and ta-C:B_5.1, 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:B_3.1 were shown as 0.055 at 23℃ and about 0.02 at 100~300℃. The specific wear rate of ta-C:B_3.1 at 23~300℃ in air was about 2.0 × 10⁻⁶mm³/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.</p>

DOI： 10.18914/tribologist.18-00003

CiNii Books

CiNii Research

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.

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

<p>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.</p>

DOI： 10.2474/trol.13.119

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CiNii Research

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

DOI： 10.1111/jace.15303

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Scopus

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

Web of Science

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

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

<p>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.</p>

DOI： 10.2474/trol.13.241

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CiNii Research

Language：English   Publisher：The Japan Society of Mechanical Engineers  

<p>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.</p>

DOI： 10.1299/mel.18-00089

CiNii Research

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

<p>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.</p>

DOI： 10.1299/jamdsm.2018jamdsm0129

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CiNii Research

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

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

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

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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

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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

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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

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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

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

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

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

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

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

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

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

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

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Language：Japanese   Publisher：Japanese Society of Tribologists  

DOI： 10.18914/tribologist.62.10_609

CiNii Research

Language：Japanese   Publisher：The Japan Society for Precision Engineering  

DOI： 10.2493/jjspe.83.319

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.16-00378

CiNii Research

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

Web of Science

Scopus

CiNii Research

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

DOI： 10.2474/trol.12.110

Web of Science

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

<p>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.</p>

DOI： 10.1299/transjsme.17-00252

CiNii Research

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 (<i>DO</i>) 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 <i>DO</i> 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 <i>DO</i> concentration. On the other hand, when the water temperature was more than 200°C, the specific wear rate drastically increased with the <i>DO</i> 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 <i>DO</i> 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 <i>DO</i> 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

Web of Science

Scopus

CiNii Research

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

Web of Science

Scopus

CiNii Research

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

<p>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.</p>

DOI： 10.1299/transjsme.16-00123

CiNii Research

Language：Japanese   Publisher：Japanese Society of Tribologists  

DOI： 10.18914/tribologist.62.07_461

CiNii Research

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.

Scopus

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DOI： 10.1299/transjsme.16-00187

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

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DOI： 10.1016/j.diamond

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DOI： 10.1299/transjsme.2014smm0182

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DOI： 20140601

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DOI： 10.1299/transjsme.2014smm0038

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ゴムと鋼の付着に両面の表面エネルギーの極性基が重要であることを示し付着力減少のための鋼の表面処理の指針を明らかにした。更に、電圧印加による付着力の新低減方法を提案した。

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Responsible for pages：37-45   Language：Japanese Book type：Scholarly book

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Event date： 2022.7

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Funchal   Country：Portugal  

Event date： 2022.7

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Malaysia  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (keynote)  

Country：Korea, Republic of  

Event date： 2020.12

Language：English   Presentation type：Oral presentation (keynote)  

Country：Malaysia  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：オンライン   Country：Japan  

Event date： 2020.9

Language：English   Presentation type：Oral presentation (keynote)  

Venue：Funchal   Country：Portugal  

Event date： 2008.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

<p>In recent years, an increase of energy efficiency of machines became worldwide request. Therefore, the reduction of friction loss in the sliding part has become an urgent issue. Generally, under high pressure conditions, the oil thickness decreases, resulting in a boundary lubrication condition where direct contact between two sliding surfaces occurs, and the friction coefficient increases. In order to reduce friction in this boundary lubrication condition, diamond-like carbon (DLC) coatings, which are carbon-based hard coatings, has many applications parts. The present paper demonstrates a fundamental study of a new method using electronic field at contact surfaces. We conducted the friction test using a pin-on-disk friction tester. The friction tester had a SUJ2 ball or ta-CNx-coated ball and a soda-lime glass plate. We used 30-μL propylene glycol (PG) as lubricant, and applied DC voltage to contact area during the friction tests. As a result, the friction test with the ta-CNx-coated ball showed a low friction coefficient but no lower friction by electronic field. On the other hand, the electric bias reduced the friction coefficient with the SUJ2 ball.</p>

DOI： 10.1299/jsmemdt.2021.20.2211

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p>It has been reported that ta-CNx coatings deposited by the IBA-FAD method show excellent low friction and wear properties, however the hardness decreases with the N/C ratio in the coating. Although, using an ion gun to mix nitrogen in the coating gives several pros to the coating, however, it rises initial cost of equipment. To overcome this situation, nitrogen ion generation by just supplying nitrogen gas close to an arc discharge area which is used in the FAD carbon ion generation was suggested by authors. The supplied nitrogen gas is ionized by the high voltage arc which is supplied to a graphite target. The effects on the N/C ratio was measured by AES, hardness was measured by nano-indentation tester, and tribological properties of the deposited ta-CNx coatings were examined. The results showed that ta-CNx coatings deposited by nitrogen gas supply method showed higher hardness than ordinally nitrogen ion beam deposition method.</p>

DOI： 10.1299/jsmemecj.2022.s114-01

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p>In this study, the effect of hardness on the wear characteristics of a-C:H films under MoDTC-containing lubrication was investigated. a-C:H films with hardness of Hv300, 600, 800 and 1200 were friction-tested with SUJ2 balls under base oil lubrication and MoDTC-containing lubrication. Under MoDTC lubrication, the a-C:H films with Hv300, 600, and 800, which have lower hardness than SUJ2 balls, showed higher specific wear than those under base oil lubrication. On the other hand, the a-C:H film of Hv1200, which has higher hardness than SUJ2 balls, shows a convex shape in the wear traces and the specific wear becomes negative. The EDS element mapping results showed that the molybdenum and sulfur reactions in the wear marks of the Hv1200 a-C:H film were clearer than those in the wear marks of the Hv300, 600, and 800 a-C:H films. The Vickers hardness of the SUJ2 balls used in this study was about Hv860, suggesting that the hardness of the mating material affects the wear properties of the a-C:H film.</p>

DOI： 10.1299/jsmemecj.2021.s116-29

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p>In recent years, the demand for lubrication in the atmosphere has been increasing, and carbon-based hard coatings Diamond-like Carbon (DLC) have been attracted attention. A tetrahedral type of DLC with tantalum (ta-C:Ta) has been exhibited ultra-low friction approximately 0.07 in the atmosphere. The friction coefficient is thought to decrease due to an increase in the graphite structure at the topmost surface which was formed by desorption of oxygen from carbon or tantalum and restructuring of carbon structure. Which is assumed to be driven by energy from the application of frictional heat or shearing. If the oxygen desorption phenomenon described above can be realized by applying energy other than friction, low friction can be obtained without friction beforehand. It has been reported that irradiating CNx coatings with ultraviolet light desorbs nitrogen atoms from the surface of the CNx coating, reducing the initial friction period by 91 %.</p><p>In this study, we clarified the effect of UV irradiation on the oxygen desorption in the ta-C:Ta0.024 coating (Ta content was 0.024) . AES and XPS revealed that UV irradiation caused C-O bond cleavage and oxygen desorption.</p>

DOI： 10.1299/jsmemecj.2022.s115-26

CiNii Research

Language：English   Presentation type：Oral presentation (general)  

<p>In this study, we created a microplastic texture by a mixture of PVC (polyvinyl chloride)-acetone and carbon black (CB) solution at an alternative high voltage. The results showed that the contact angle when high voltage of 2 kV was applied was greater than that when no voltage was applied, and the surface contact angle showed a maximum of 142° when the CB concentration was 1.5 wt.% and the applied frequency was 0 Hz, while the surface head convex structure was found when the CB was 1.5 wt.% at 10 Hz when observed by field emission scanning electron microscopy (FE-SEM). And it was found that the surface spherical structure was sharper when the frequency was applied at 10 Hz than 5 Hz.</p>

DOI： 10.1299/jsmeiip.2022.iip2r3-h08

CiNii Research

Language：Japanese   Presentation type：Oral presentation (general)  

<p>Two phase lubricant has attracted attention as a lubricant oil with little change in viscosity with temperature change. The two phase lubricants 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 is used as a high viscosity lubricant for two phase lubricant. In the high temperature region, PAG is mixed into mineral or synthetic base oil and the viscosity reduction is relieved. However, with this two phase lubricant, 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 using a reflection spectroscopic film thickness meter. In addition, focusing on the difference in molecular structure between PAG and PAO, oil film analysis was carried out using an oil film model having a three-layer structure in which a PAG adsorption layer having a functional group and a polar molecule exists. As a result of using two phase lubricant, it was shown that the frictional characteristics with temperature change are different.</p>

DOI： 10.1299/jsmemecj.2018.s1110201

CiNii Research

Presentation type：Oral presentation (general)  

Language：English   Presentation type：Oral presentation (keynote)  

Country：Malaysia