Friction and wear thresholds of alumina-chromium steel pairs sliding at high speeds under dry and wet conditions

Abstract

Friction and wear of alumina sliding against two chromium steels and against itself under dry and wet conditions are reported. Tests were performed using a pin-on-disc device. Loads and speeds, respectively, ranged from 5 to 300 N and 3 to 10.7 m/s. The evolution of the friction coefficient and wear rates point to the existence of a load threshold correlated with the sudden degradation of the ceramic under both wet and dry conditions. Below the threshold, the ceramic remains undamaged while steels exhibit a moderate wear rate. Worn surfaces show thickening metallic transfer on the ceramic and abrasion grooves on steels. Above the threshold, the ceramic damage is induced by grain boundaries failure which leads to a coarse roughness and the release of abrasive particles. The circulation of the latter increases the steel wear and reduces the metallic transfer thickness on the ceramic. Water in the contact zone significantly lowers the threshold value and the friction coefficient value. The mechanical, thermal and chemical effects of load, speed and water are discussed with regard to damage undergone by the sliding bodies. A particular emphasis is focused on the calculation of average and maximum temperatures occuring in the contact area in relation to ceramic grain boundary damage.