The Run-in Process for Stable Friction Fade-Out and Tribofilm Analyses by SEM and Nano-Indenter

Abstract

It was shown in previous reports by authors that friction coefficients of the level of 0.0001 were achieved when ZrO2 (Y-PSZ: yttria partially stabilized zirconia) pins were slid against diamond-like carbon (DLC) films in H2-gas environment under heavy applied load of 63.7 N (friction fade-out, FFO). It was also shown that FFO continued long when the main H2-gas flow was mixed with a small amount of aqueous-alcohol vapor. A tribofilm was formed at the contact area of ZrO2 surface, and it was considered that the aqueous-alcohol vapor made the tribofilm strong. In the present research, the run-in process for achieving more stable FFO is investigated by varying the run-in pattern consisting of load step-up and aqueous-alcohol vapor addition, and the stable FFO continuing several hours is realized reproducibly. Then, before and after the FFO onset, the contact area on ZrO2 surface is observed by SEM, and nano-indentation hardness of tribofilm is measured. It will be shown that a substance made of hydrocarbons with low melting temperature, low electrical conductivity and low nano-indentation hardness such as hydrocarbon polymers is formed on the tribofilm, suggesting the evolution of hydrocarbon gas at the sliding surface.

Keywords

• dlc
• run-in
• zirconia
• h2 gas environment
• catalytic reaction
• friction fade-out
• tribofilm
• contact stiffness