Comparison of fretting wear of Cr-rich CrN and TiN coatings in air of different relative humidities

The CrN and TiN coatings deposited on tool steel substrates by ion beam assisted deposition (IBAD) and triode ion-plating techniques, respectively, were investigated. The fretting wear of these coatings has been determined in air of different relative humidities (RHs). The results show that the coefficient of friction of the CrN coatings versus corundum at 50 and 85% RH is about 0.3, slightly higher than that of the TiN coatings. However, the TiN coatings exhibit a high coefficient of friction of about 0.8 at RH<10%, while the CrN coatings present a much lower coefficient of friction of about the same level as at the high RH. In addition, the volumetric wear loss of the CrN coatings is small compared to the TiN coatings especially at the low RH. The wear rate expressed as wear volume per dissipated energy indicates that the CrN coatings possess better fretting wear resistance than the TiN coatings. Based on these properties, the CrN coatings should be preferred for fretting contacts against corundum, especially in very dry environments.