Faculty Profiles - UMEHARA, Noritsugu

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

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

Tribology letters Vol. 70 page： 118 2022.10

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

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

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

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

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

DOI： 10.18914/tribologist.22-00001

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

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

Tribology International Vol. 169 page： 107486 - 107486 2022.5

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

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

DOI： 10.1016/j.triboint.2022.107486

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

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

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

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

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

DOI： 10.1177/13506501211013126

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

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

Tribology International Vol. 168 page： 107404 - 107404 2022.4

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

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

DOI： 10.1016/j.triboint.2021.107404

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

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

Tribology International Vol. 168 page： 107450 - 107450 2022.4

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

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

DOI： 10.1016/j.triboint.2022.107450

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

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

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

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

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

DOI： 10.18914/tribologist.21-00018

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

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

Friction Vol. 10 page： 1596 - 1634 2022.1

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

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

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

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

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

DOI： 10.25162/VSWG-2021-0016

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

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

TRIBOLOGY INTERNATIONAL Vol. 162 page： 107128 2021.10

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

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

DOI： 10.1016/j.triboint.2021.107128

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

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

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

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

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

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

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

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

DOI： 10.18914/tribologist.21-00001

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

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

Tribology International Vol. 159 page： 106944 - 106944 2021.7

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

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

DOI： 10.1016/j.triboint.2021.106944

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

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

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

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

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

DOI： 10.18914/tribologist.20-00020

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

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

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

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

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

DOI： 10.1115/1.4050269

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

M. Murashima, T.Tokoroyama, N. Umehara

Tribology International Vol. 156 page： 1 - 9 2021.5

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

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

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

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

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

DOI： 10.1021/acs.langmuir.0c03435