FRICTION AND WEAR BEHAVIOR 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 wer e performed in a wide speed range of 0.125-8 m/s under different norma l loads using a block-on-ring tribometer. SEM, EDS and XPS were employ ed to identify the mechanical and chemical changes on the worn surface s. A tangential impact wear model was proposed to explain the steep ri sing of wear from the minimum wear to the maximum wear. The results sh ow that the wear of Cr2O3 coatings increases with increasing load. Sec ondly, there exist a minimum-wear sliding speed (0.5 m/s) and a maximu m-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 ra nge 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 imp act effect at median speeds and the softening effect of flash temperat ure 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