Friction and wear behaviour of plasma-sprayed Cr2O3 coatings against steel in a wide range of sliding velocities and normal loads

This study investigates the influence of sliding speed and normal load on the friction and wear of plasma-sprayed Cr2O3 coatings, in dry and lubricated sliding against AISI D2 steel. Friction and wear tests were performed in a wide speed range of 0.125-8 m/s under different normal loads using a block-on-ring tribometer. SEM, EDS and XPS were employed to identify the mechanical and chemical changes on the worn surfaces. A tangential impact wear model was proposed to explain the steep rising of wear from the minimum wear to the maximum wear. The results show that the wear of Cr2O3 coatings increases with increasing load. Secondly, there exist a minimum-wear sliding speed (0.5 m/s) and a maximum-wear sliding speed (3 m/s) for a Cr2O3 coating in dry sliding. With the increase of speed, the wear of a Cr2O3 coating decreases in the range 0.125-0.5 m/s, then rises steeply from 0.5 m/s to 3 m/s, followed by a decrease thereafter. The large variation of wear with respect to speed can be explained by stick-slip at low speeds, the tangential impact effect at median speeds and the softening effect of flash temperature at high speeds. Thirdly, the chemical compositions of the transfer film are a-Fe2O3 in the speed range 0.25-2 m/s, and FeO at 7 m/s. In addition, the wear mechanisms of a Cr2O3 coating in dry sliding versus AISI D2 steel are adhesion at low speeds, brittle fracture at median speeds and a mixture of abrasion and brittle fracture at high speeds. Finally the lubricated wear of Cr2O3 coating increases sharply from 1 to 2.8 m/s. Copyright (C) 1996 Elsevier Science Ltd