An energy description of hard coating wear mechanisms

Numerous hard coatings have been developed to improve the wear resistance of sliding components under dry or lubricated conditions. High microhardness is usually required to resist abrasion wear mechanisms. However, microhardness cannot be considered as a sufficient parameter to design a tribological application. Wear analysis and friction coefficient identification are systematically required. To quantify the wear kinetics, the Archard approach is classically applied. It relates the wear volume with the product of the sliding distance and the normal load. A wear coefficient is then extrapolated and is supposed to establish the wear resistance of the material studied. The present study shows that this approach does not work when the friction coefficient is not constant. It appears to be much more relevant to consider the interfacial shear work dissipated through the contact as a significant wear parameter. This approach is transposed in the most convenient way to study the wear response of a sintered steel and then extend it to the study of different coatings, TiN, TiCVC, and a high-speed steel substrate for gross-slip fretting conditions. The identification of wear-energy coefficients permits classification of the wear resistance of the tribosystems studied. This involves identifying the partition of the total dissipated energy consumed through the different damage processes, and relating that with physical variables, such as the binding energy, the energy activation for oxidation and mechanical energy.