Transient wear of silicon nitride in lubricated rolling contact

Wear of silicon nitride balls and rods was studied in lubricated rolling co ntact using a bah-on-rod rolling contact fatigue (RCF) tester. The wear res ponse of both the elements, balls and rods, was transient. The nature of th e transient was dependent on the initial surface roughness of the rod, whil e the total volume loss increased with the initial contact stress. Bearing- grade balls (R-a = 0.005 mu m) rolling on as-ground (R-a = 0.18 mu m) rods produced a high initial wear rate in both elements that decreased exponenti ally with time or number of loading cycles. Improving the surface finish on the rods by lapping (R-a = 0.05 mu m) produced delayed wear in both elemen ts; i.e., the wear rate was initially zero during an incubation period, the n, increased and, finally, decreased. The role of decreasing contact stress in the transient wear, and the micromechanisms of wear involving a triboch emical reaction are discussed. (C) 1998 Published by Elsevier Science S.A. All rights reserved.