The discovery of tribochemical reactions at the sliding interfaces has suggested new pathways for material synthesis. This study explored the formation of thin functional films at the steel-on-silicon sliding interfaces, with toluene as base liquid and five different additives i.e. Zinc dialkyldithiophosphates (ZDDP), 3-Aminopropyltriethoxysilane (APTES), Octadecyltrimethoxysilane (OTMS), (3-mercaptopropyl) trimethoxysilane (MPTMS) and Octadecene. All additives were found to result in thin functional films of varying chemical, mechanical, and electrical characteristics. The Octadecene and OTMS APTES produced carbon rich tribofilms. The OTMS tribofilms were soft, as revealed by the quantitative nanomechanical analysis. The MPTMS and ZDDP additives resulted in conductive thin films in a well-defined linear pattern. The MPTMS resulted in continuous conductive films with surface coverage higher than that of the ZDDP.

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The reaction pathways of Cu oxidation by the chemical mechanical polishing (CMP) slurry containing ceria (CeO₂) abrasive grains were theoretically investigated. First-principles molecular dynamics (FPMD) simulations were employed to analyze the reaction pathways between a CeO₂ surface and a Cu surface. As a result, the following reactions were observed: chemical bonds between CeO₂ and Cu were formed, electron transfer from Cu atoms to Ce atoms occurred, a water molecule dissociated on the CeO₂ surface to form a proton and an OH⁻ ion, and the generated OH⁻ ion formed Cu-O bonds with the oxidized Cu atoms. The candidate reaction pathways for Cu oxidation, including those observed in FPMD simulations, were further analyzed by constructing energy diagrams using density functional theory (DFT) calculations. As a result, the reaction pathway observed in the FPMD simulation was identified as the most likely candidate, having the lowest activation energy and the lowest final structure energy. These results indicate that the oxidation reaction pathways of Cu in the slurry containing CeO₂ abrasive grains involve electron transfer through the formation of chemical bonds between CeO₂ and Cu, as well as the supply of oxygen atoms derived from water to Cu atoms.

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The high-power impulse magnetron sputtering (HiPIMS) is a deposition method that has potential to achieve both high hardness and high surface smoothness of diamond-like carbon (DLC) films, and investigation has been performed to optimize the deposition process. However, the dominant HiPIMS process factors that affect the hardness and wear properties of DLC films have not been clarified based on the observation of plasma properties. In this study, we focused on the sputtering gas species that affect the densities of carbon ions in the plasma and the target magnetic field strength, which affects the ion transportation and its incident flux onto the deposition substrate. The results of this investigation reveal that the addition of neon to the conventional sputtering gas of argon promoted carbon ionization and the incident carbon ion flux on to the substrate was increased by suppressing the back attraction of carbon ions to the target in a weak magnetic field strength. It was also confirmed that these effects could potentially improve the hardness and wear properties of DLC films.

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In this research, we investigated biodegradable hydraulic oil temperature characteristics by using an oil sensor and verified the correlation between sensor measurement values and oil properties as biodegradable hydraulic oil deteriorated, to apply oil condition monitoring to biodegradable hydraulic oil. The test results of temperature characteristics showed that biodegradable oil and mineral oil had equivalent kinematic viscosity characteristics. In contrast, the density of biodegradable oil was approximately 1.05 times that of mineral oil, and the dielectric constant was approximately 1.5 times that of mineral oil, showing a linear change trend with temperature change. This confirms that temperature correction is possible using the same method as used for mineral oil. Test results for degradation showed that, for biodegradable hydraulic oil, the change rate for total acid number increase in the sensor value was smaller than that for mineral oil, indicating that a new evaluation criterion is needed. Furthermore, it was confirmed that mineral oil, biodegradable oil, or a mixture of the two can be roughly estimated in a hydraulic excavator by using the characteristics of the difference in density and dielectric constant between biodegradable oil and mineral oil.

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Top-view in-situ scanning electron microscopy (SEM) images of the friction interfaces between an electron-transparent film and a polyacetal (POM) pin surface revealed the formation of transfer layers, wear debris (including rolling debris), and freestanding layers; however, the relationship between these phenomena and friction forces remains unclear. In this study, friction forces were estimated from SEM images using a convolutional neural network (CNN). The estimated friction forces closely matched the measured values. The specific regions in the SEM images that contributed to CNN friction force estimation were identified using gradient-weighted class activation mapping (Grad-CAM). These regions were primarily located around the contact surface rather than on the contact surface. Furthermore, to investigate the specific contact surface features associated with lower and higher friction forces beyond those observed in the friction test, fake top-view in-situ SEM images were generated with continuous and arbitrary friction forces, including values outside the experimental friction force range, using a continuous conditional generative adversarial network. The generated SEM images successfully reproduced the experimental features corresponding to the friction forces within a range for which sufficient experimental data were available.

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Amorphous SiC (a-SiC)-based coatings containing not only Si–C bonds but also C–Si–O, C–C, and Si–O₂ bonds were deposited on Al₂O₃ substrates via pulsed laser deposition. Sliding tests using SiC ceramic balls in normal saline revealed that the coating exhibited a low friction coefficient of 0.05-0.06 at a shorter running-in process than SiC bulk ceramic plates. The specific wear rate of the coating was also lower than that of the SiC plate. Reactive molecular dynamics simulations revealed that the C–Si–O bonds in the coating facilitated the generation of Si–O units, which contained Si–O bonds but no Si-C bonds, through tribochemical reactions with water, resulting in superior tribological properties in normal saline compared to those of SiC plates. These findings demonstrate that a-SiC-based coatings containing C–Si–O bonds are promising as low-friction and low-wear coatings for biomedical implants such as ceramic joint prostheses.

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The efficiency of electric vehicles (EVs) can be further enhanced by increasing the rotational speed of their motors. However, higher motor speeds may reduce the fatigue life of gear teeth, particularly through the formation of micropitting. While the slip-roll ratio (SRR) is known to influence micropitting, its precise effect on this type of surface damage remains insufficiently understood. In this study, we investigated the influence of SRR on the occurrence of micropitting in disk specimens lubricated in base oil (PAO4) and e-axle fluid environments. Friction tests were conducted using a ball-on-disk setup, in which steel disks with two different surface roughness levels were tested under various slip ratios. A binarization method was employed to quantify the extent of micropitting. The results showed that both micropitting and wear are highly dependent on SRR and surface roughness. In the PAO4 environment, significant micropitting occurred at 0% SRR and decreased with increasing SRR, suggesting that sliding wear may suppress fatigue wear. In the e-axle fluid environment, significant micropitting was also observed at 0% SRR, but the wear pattern showed a broader distribution, indicative of chemical wear.

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This study presents a comprehensive investigation into the microstructural evolution and tribological performance of 316L stainless steel (SS316L) components fabricated by Laser Powder Bed Fusion (LPBF), enhanced through nitriding and hybrid thermochemical surface treatment. The hybrid process which involves simultaneous diffusion of nitrogen and carbon, resulted in the formation of a single, homogeneous expanded austenite (S-phase) layer with a thickness of 12.2 μm, over six times thicker than the 1.98 μm layer formed through nitriding alone. This study is among the first to evaluate hybrid thermochemical treatment on LPBF 316L, addressing a gap in surface engineering strategies for additive manufacturing. X-ray diffraction confirmed significant lattice expansion indicative of dual interstitial incorporation. Microhardness measurements confirmed the enhancement, with the hybrid-LPBF specimen achieving a peak surface hardness of ~1209 HV compared to ~345 HV for nitride-LPBF specimens and ~265–297 HV for untreated conditions, representing a nearly fivefold enhancement. Then, tribological testing under dry sliding conditions revealed that the hybrid-LPBF specimens achieved the lowest coefficient of friction (COF = 0.45) and negligible wear depth, outperforming both nitride-LPBF (COF ~ 0.60, wear depth ~ 18 μ μm) and untreated-LPBF specimens (COF = 0.77, wear depth ~ 40 μm). Counter face analysis further showed reduced material transfer and smoother wear scars in treated specimens especially hybrid-LPBF. These findings demonstrate that hybrid thermochemical treatment significantly mitigates the surface limitations of as-built LPBF components, offering a significant potential to enhance the wear resistance and operational durability of stainless steel parts for high-demand applications. Future research will explore anisotropic behaviour and simulation-based optimization of treatment parameters.

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