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Improving the wear resistance of polymer-based materials can lead to high energy efficiency of transport machineries owing to the higher strength-to-weight ratio. Oxidized wood-utilized synthesized copper-based particles (OWCu) was incorporated into epoxy resin to investigate its effect on the wear resistance of OWCu-incorporated epoxy with the steel counterpart using a ball-on-plate tribometer. OWCu was mainly composed of CuO with a small amount of graphitic carbon, and the average particle size was approximately 0.5 μm. A higher wear resistance was observed for the OWCu-incorporated epoxy at more than 0.6 mass% compared to the neat epoxy. The mechanism for the improvement of the wear resistance property was discussed, and it was revealed that the surface roughness of the steel counterpart was maintained at a low level for the OWCu-incorporated epoxy, which played a dominant role in reducing the wear of the OWCu-incorporated epoxy. The polishing effect of OWCu could reduce the surface roughness of the steel counterpart in the friction process. In addition, at higher concentrations of more than 5.0 mass%, OWCu adhered to the steel surface, which decreased the wear of the steel surface. OWCu is a promising material to enhance the wear resistance of polymer-based materials, especially with low elongation.

Carbon nanomaterials have been studied for their promising tribological properties under boundary lubrication. However, the behavior of carbon nanomaterials upon entering narrow friction interfaces under boundary lubrication is poorly understood. In this study, to clarify how graphene oxide (GO), which is one of the carbon nanomaterials, enters and works on a friction interface under boundary lubrication, in situ observations of a friction interface between an SUJ2 ball and soda glass-lime disk in a GO water dispersion, with a load of 1 N, were conducted using optical microscopy. Isolated dispersed GO accumulated only in front of the contact areas. GO accumulations formed, grew, and peeled off due to the friction. Although the GO accumulations were significantly unstable, they functioned as friction reduction and anti-wear. We firstly found that the unstable GO lubricating accumulations that formed in front of the contact areas were able to widen between the ball and the disk similar to a wedge; this wedge effect would cause a decrease in friction and wear. Unlike the wedge effect under hydrodynamic lubrication, the GO accumulations that functioned as the wedge stayed on the ball surface.

Copper based particles were synthesized by a wood-powder-template-based process. Wood powders mixed with an aqueous cooper salt solution were heated under N2 gas flow, and then, the mixture of the charcoal powder and copper particles were heated in air to remove charcoal. Finally, oxidized wood-derived copper particles (OWCu) of less than 1 μm were synthesized. Wood powders acted as the template and limited the sizes of the copper particles. In addition, the tribological properties of OWCu in synthetic oil were investigated using a pin-on-plate reciprocating tribometer. Our results revealed that 0.5 mass% OWCu reduced both the friction coefficient (max 45%) and wear volume (max 39%) of SUJ2 lubricated by PAO4. The best reduction effect was obtained for OWCu synthesized at 400°C under N2 gas flow, which had the smallest average particle size, where the coverage of the OWCu layer on the wear track was the largest. These facts suggest that the particle size reduction of OWCu can increase the coverage and improve the friction coefficient and wear volume reduction effects of the lubricant. Control of the wood-powder-template-based synthesized particles to the optimal size for the roughness of the sliding surface would help achieve better tribological performance.

Graphene oxide (GO) and oxidized wood-derived nanocarbon (oWNC) were dispersed in an epoxy resin to improve the mechanical and tribological properties of an epoxy resin. Mechanical properties of the GO/epoxy (GO/EP) and oWNC/epoxy composites (oWNC/EP) were investigated by tensile tests and nano-indentation. Under dry, water, and oil lubrication conditions, friction coefficients and wear volumes of these composites were measured. GO has single-layered structure. oWNC has chain-like nanostructures, and the nanochains are aggregated. GO and oWNCs have same surface chemical composition due to the same oxidation treatment. Thus, in this study, the structure and morphology dependences of the nanocarbons in mechanical and tribological properties will be appeared when the nanocarbons were used as the additives in the resin. The tensile strength, tensile modulus, and hardness increased by 20%, 63%, and 35% in maximum by the addition of GO and oWNC to the epoxy resin, respectively. Moreover, the wear resistance of GO/EP and oWNC/EP was enhanced compared to that of a neat epoxy. The reduction rates of the wear volume for 5.0 mass% GO/EP and 1.0 mass% oWNC/EP achieved to 91% and 67%, respectively. Comparing GO and oWNC, oWNC effectively reduced the friction coefficient and wear at a lower concentration. The improvement of tribological properties after the addition of the oxidized nanocarbons can be attributed to the increase in the hardness and lubricity of the composites.

In this study, a novel method was developed for in situ scanning electron microscopy (SEM) observations of friction interfaces, from a top view, using a Si3N4 thin film (SiN film), which has high electron transmission ability, and a microtribometer. Nanodiamond (ND) aggregates were adsorbed on the back surface of the SiN film. A JIS-SUS304 ball, on which surface ND aggregates were adsorbed and tribofilms were already formed, contacted and slid with the back surface of the SiN film. An SEM electron beam went through the SiN film, and generated secondary electrons from the ball surface contacting the back surface of the SiN film and the adsorbed ND aggregates. Thereafter, the generated secondary electrons from the ball surface penetrated again through the SiN film and reached the SEM electron detector. In other words, the contacting ball surface and the adsorbed ND aggregates were successfully imaged through the SiN film. Energy dispersive X-ray spectroscopy analyses of the friction interfaces were also accomplished. Moreover, in situ SEM observations of friction interfaces under boundary lubrication, using poly-alpha olefin (PAO) oil with graphene oxide aggregates and lithium grease with MoS2 particles, were successfully accomplished. The PAO oil and lithium grease had electron transmission ability, and the friction interfaces were imaged by SEM as seen with an optical microscope.

The influences of interactions between C60 thin films and Si substrates were investigated using atomic force microscopy (AFM). It was found that higher friction coefficient was obtained at the C60 domains formed on the H-terminated Si(001) substrate and lower ones on the Si(001)-2×1 substrate. Moreover, lowest friction coefficient was found for the C60 film on the Si(001)-2×1 remained after scratching. Therefore, it is thought that higher interactions between C60 and Si substrate caused lower friction coefficient of C60 thin film. The prepared substrate was examined by reflection high energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES).