Wear Transition of CrN Coated M50 Steel under High Temperature and Heavy Load

The combination of high temperature indentation and wear test provides a useful way to investigate wear of CrN coating and wear transition mechanisms. In this paper, the high temperature hardness of CrN coatings and load bearing capacity, Lb, of CrN coated M50 disks were determined from spherical indentation at temperatures up to 500 °C. Wear tests with different normal loads were carried out at the same temperatures as the indentation tests. The results show that wear mechanism of CrN coating changes with external load, P, and temperature, T. Under a tested condition of P < Lb and T < 315 °C, abrasive is the dominant wear mechanism for CrN coating. Under a tested condition of P < Lb and T ≥ 315 °C, wear of CrN coating transitions into mild oxidation wear due to the lubricating effect of chromium oxide film. Under a tested condition of P > Lb and T < 315 °C, wear of CrN coating was controlled by coating fracture. Under a tested condition of P > Lb and T ≥ 315 °C, wear of CrN coating transitions into the severe wear mode, due to the tensile fracture of oxidation films, thereby leading to adhesion between CrN coating and tribo-counterpart. The presented method can be helpful in predicting permissible load and working temperature in tribological applications of CrN coating.