Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 25, 2025 - November 29, 2025
Diamond films have excellent properties such as high hardness, low friction, and high wear resistance; therefore, it is used in sliding parts such as mechanical seals. However, due to the rough surface, polishing after deposition incurs significant costs. In recent years, by increasing the CH4 concentration during diamond film synthesis, smooth surfaced nanocrystalline diamond (NCD) films have been obtained. However, due to their lower hardness, their wear resistance decreases. we developed a method to synthesize diamond films while modulating the carbon gas concentration. Moreover, the effects of concentration modulation on the friction and wear properties of diamond films synthesized via microwave plasma chemical vapor deposition (CVD) when using SiC, a material actually used in mechanical seals, as the counterpart material. CH4-H2 gas was used as the source gas. A concentration-modulated diamond (CMD) film was synthesized by modulating the methane concentration from 1% to 10%, which exhibited a surface roughness (Sa) of 20 nm and a hardness of 65 GPa. In friction testing with SiC as the counterpart material under dry conditions, the friction coefficient of the CMD film was below 0.5. The specific wear rate of the SiC ball was 0.8 mm³/Nm, which indicates a reduction in the wear of the counterpart material compared to conventional MCD films. Furthermore, the specific wear rate of the CMD film was 3.8 μm³/Nm, showing a decrease in the film's wear compared to conventional NCD films.
