Comparison of wear and corrosion wear of TiN coatings under uni- and bidirectional sliding

Abstract

A comparative study was made of the friction and wear behaviour of PVD TiN coatings sliding against corundum counterbody in 50% RH air, in demineralized water, and in a II,PO, solution. Unidirectional sliding tests (pin-on-disk) were performed in two different pin-on-disk geometries operated under the same test parameters (5 N, 0.2 m s(-1)). Bidirectional sliding tests (fretting) were performed under gross slip conditions (5 N, 10 Hz, 100 mu m). Results on TiN coatings show that in bidirectional sliding tests, the coefficient of friction is lower, and the wear rate is higher than in unidirectional tests both performed in air and water. The evolution of friction is almost the same for the two unidirectional set-ups when tested in air. However, when tested in water and in phosphoric acid solutions, a significant difference in friction is noticed between the two unidirectional set-ups. The wear mechanisms identified are a mild tribo-oxidation mechanism in air and water, and a lubricating triboactivated phosphation mechanism in H3PO4. From these results, H3PO4 appears as a potential candidate for oil-free lubrication in uni- and bidirectional wear. (C) 1999 Elsevier Science S.A. All rights reserved.