The friction properties of wet clutches were investigated using lubricant oils containing polybutenyl succinimide (PBSI) as a dispersant and oleyl sarcosine (OS) as an oiliness agent in base oils such as paraffinic mineral oil and polyalpha-olefin. The concentration of the additives in lubricant film at sliding contacts was measured by in-situ observation with a micro Fourier transform infrared spectroscopy (FT-IR). It was found that the concentration of additives was increased at sliding contacts and was dependent on load, sliding speed and additives. The friction coefficients were changed by the addition of the additives and dependent on sliding conditions. The friction coefficient was decreased at lower sliding speed by the addition of OS, whereas it was increased at higher sliding speed by the addition of PBSI. A friction mechanism was proposed on the basis of the lubricant film viscosity which is dependent on the concentration of additives.

Sintered aluminum-silicon (Al-Si) disks were slid against silicon nitride (Si₃N₄) pins in n-hexane, in ethanol and in ethanol-n-hexane mixtures to evaluate the influence of the ethanol content in ethanol-gasoline fuels on the friction and wear behavior. Friction and wear of sintered aluminum-silicon in n-hexane were higher than those in lubricants containing ethanol. Worn surfaces indicated that oxidative wear, abrasive wear, adhesive wear and brittle fracture of silicon particles took place on the sliding surface of the sintered Al-Si disk in n-hexane. Precipitation of oxidized aluminum and oxidized silicon on the sliding surface, abrasive wear, plastic deformation and adhesive wear were inhibited by the presence of ethanol. Friction and wear of sintered Al-Si disks in lubricant with high ethanol content were lower than those in lubricant with low ethanol content. Wear of Si₃N₄ pin in n-hexane was too small to be measured. Tribochemical wear of Si₃N₄ pins took place in lubricants containing ethanol.

Structural and mechanical properties of diamond-like carbon (DLC) films were evaluated by Raman spectroscopy. Also, we showed that Raman spectroscopy can be used as a predicting tool of hardness of DLC films deposited on three-dimensional target. DLC films were prepared by bipolar plasma based ion implantation and deposition, and the positive and negative pulse voltages were varied from 1 to 3 kV and from −1 to −15 kV, respectively. With an increase in the pulse voltages, the Raman G-peak position and I(D)/I(G) ratio increased, and the G-peak full width at half maximum〔FWHM(G)〕decreased, indicating graphitization of the DLC films. In the low-wavenumber regime, the FWHM(G) increases when the G-peak shifts to higher wavenumbers, reaching a maximum value at around 1540 cm^-1, and then decreases. This behavior was due to the structural changes occurring in the DLC films with an increase in the wavenumber. DLC to polymer-like carbon (PLC) transition occurred in the low-wavenumber regime, and DLC to graphite-like carbon (GLC) transition occurred in the high-wavenumber regime. Further, two different trends were observed in the relationship between the mechanical properties of the DLC films and the FWHM(G), originating from the structural change from DLC to GLC and PLC. The hardness of DLC films coated on a steel rod was successfully predicted by a Raman parameter of FWHM(G).