Yasunori Niiyama

Friction and Delamination Properties of Self-Mating Diamond-Like Carbon Coatings in Water

AbstractThe friction and delamination properties of self-mating diamond-like carbon (DLC) coatings in water and ambient air were investigated using a ball-on-disk tribometer. An a-C:H-type DLC coating was deposited on SUJ2 bearing steel using plasma chemical vapor deposition. Delamination of DLC coatings occurred in water in relatively mild contact conditions, such as applying a low load and a high sliding speed. However, no delamination occurred under severe contact conditions. Furthermore, delamination never occurred under ambient air conditions. The process that prevents delamination occurring under ambient air conditions is clarified using a detailed analysis of SEM data. Micro-cracks were caused by Hertzian contact with droplets, which then propagated into large ruptures under water conditions; however, they disappeared and formed a smooth surface under ambient air conditions. This is because of the structural change to an sp2-rich surface. Enhancement of the structural change of DLC coating could suppress delamination in water.

Effect of Sliding History on Super-Low Friction of Diamond-Like Carbon Coating in Water Lubrication

Water lubrication using diamond-like carbon (DLC) coatings is regarded as being a promising eco-friendly technology. However, it has been reported that delamination of DLC coatings occurs in water. The authors clarified that the application of friction in ambient air prior to self-mating DLC water lubrication, in addition to the suppression of DLC delamination, caused the friction coefficient to decrease more than when no processing is performed in the boundary lubrication region. When compared to the case when there was no pre-sliding, in terms of the wear scar, in this case, a much more hydrophilic and smoother surface was formed. Therefore, the friction-reducing process in water due to the presence of a sliding history (pre-sliding in ambient air) was clarified by an analysis of the DLC geometry, structure, chemical state and an in situ analysis that can measure the friction properties and the chemical state of DLC. We clarified that the process in which the oxidation and structural changes of the DLC proceed at the time of pre-sliding in ambient air using in situ Fourier transform infrared spectroscopy–attenuated total reflection. It was also revealed that the OH termination subsequently accelerated rapidly due to the friction in water after pre-sliding process. In addition, a time-of-flight secondary ion mass spectrometry analysis revealed that this OH group was derived from the lubricating water and unlike the case in which there was no pre-sliding in ambient air, the rate at which OH terminates increased considerably.

A Liquid-Piston Steam Engine

A liquid-piston steam engine is suitable for waste heat recovery from automobile exhaust gas since it has high efficiency at low temperature region and high reliability at high temperature. In this work, heat loss from heating section inlet is investigated and new structure is proposed to reduce this heat loss. In addition, the effect of coolant temperature on thermal efficiency is investigated and an opposite trend of conventional thermal engines is found. Thermal efficiency of 8.8% at heating temperature of 270 ̊C, cooling temperature of 90 ̊C and operation frequency of 3Hz is achieved with the improved liquid-piston steam engine.