Effect of transfer layer and film structure on friction properties of DLC coating at high temperature

Abstract

Diamond-like carbon (DLC) coatings has found widespread application as a protective coating in many fields because its high hardness, low friction, chemical inertness and other properties. It was reported that tetrahedral amorphous carbon (ta-C) coatings showed lower friction at high temperature than at ordinary temperature. But the mechanism of ta-C coatings' lower friction at high temperature is not clarified. In this study, we clarified the effect of transfer layer and film structure on friction properties at high temperature. We conducted friction test at five temperature environment (23 ~ 400 ℃) and analyzed transfer layer. From the result, friction coefficient of ta-C coatings decrease with test temperature increase and friction coefficient of ta-C coatings become same value at over 200 ℃. And friction coefficient decrease with thickness of graphitized transfer layer calculated by atomic force microscope (AFM) become thicker. We also deposited three kind of sp₃ bonding ratio ta-C coatings by changing bias voltage in T-shaped filtered arc deposition (T-FAD) method. And we conducted friction test at 200 ℃. From the result, friction coefficient of fewer sp₃ bonding ratio decreased.