Friction and wear behaviour of CrN coating at temperatures up to 500 °C

CrN coatings prepared by low arc deposition technology on hardened steel substrates were studied in this paper. Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 500 °C in order to prevent significant softening of substrate. Evaluation of friction coefficient with the number of cycles was measured at different temperatures and the wear rates of coatings and balls were determined. Three different materials were used as counter-parts: 100Cr6 bearing steel, Si3N4 and Al2O3 balls with a diameter of 6 mm.The coating microstructure was studied by X-ray diffraction (XRD) measured in situ up to 600 °C; the chemical composition was obtained by energy dispersive X-ray analysis (EDX). Mechanical properties of these coatings were studied by scratch and microhardness testing. Morphology of coating surface, ball scars, wear tracks and wear debris were examined by scanning electron microscopy (SEM).The experiments have shown strong dependency of tribological parameters on temperature. Wear of CrN coating sliding against the 100Cr6 ball was not measurable. Generally, the wear rate of coating increases with temperature when sliding with ceramic balls. The wear debris analysis has shown that the tribochemical wear is dominant at high temperature (Si3N4 balls), while the sliding process with the Al2O3 balls can be described as a three-body wear with the wear particles consisting mainly of chromium oxides conglomerated into relatively homogenous layer protecting coating from rapid wear. The average dimension of wear particles decreases with temperature, while the protecting layer thickness increases.