The effect of humidity on friction behavior of hydrogenated HIPIMS W-C:H coatings

Abstract

The study of the effect of humidity on friction behavior in HiPIMS (High Power Impulse Magnetron Sputtering) W-C:H coating/steel ball system confirmed the formation of transfer layer adhered to the ball and consisting of hydrogenated carbon, ferritungstate and small amounts of tungsten (sub)oxides and iron oxides. The corresponding mechano(tribo)chemical reactions driven by flash temperature in the sliding asperities involved oxidation, water vapor dissociation and carbon hydrogenation. Such composition agreed with the results of modelling based on the minimization of free Gibbs energy in the mutually interacting thermochemical reactions. The applicability of modelling to friction was attributed to fast reactions among microscopic asperities eliminating kinetical factors. In inert atmospheres, oxidation and hydrogenation were suppressed and friction seemed to be controlled by the amount of additional carbon.