Water-lubricated and dry sliding wear of yttria stabilised zirconia and silicon carbide couples Part I: Wear rates

Yttria stabilised tetragonal zirconia polycrystal (YTZP) pins were subjecte d to sliding wear against sintered silicon carbide discs using a high speed pin-on-disc machine. For each test, a single flat-ended pin was worn at a relative sliding speed of 6 m s(-1) against a disc held in the chuck of a l athe. Experiments were conducted under water-lubricated and unlubricated co nditions. Wear rates of the pin were measured by mass loss. Under water-lub ricated conditions, the wear rate was extremely geometry-dependent and the alignment of the polished pin determined the amount of wear, causing scatte r in the results of nominally identical tests. Under dry conditions, an ord er of magnitude higher wear rate of the pin was observed. Under water-lubri cated conditions, no wear was measured for pins that were polished flat in situ on the rig, suggesting that hydrodynamic lubrication was achieved. Hig her pressures up to 70 MPa were then employed on pins with reduced surface area to investigate the breakdown of the lubrication regime and subsequent wear of the pin. Disc wear was more difficult to quantify, due to transfer of YTZP from the pin, but was less severe than for the YTZP leading to a ge neral smoothing of the surface. Scanning electron microscopy was used to ex amine the sliding surfaces and elucidate likely wear mechanisms. This techn ique revealed a milder YTZP wear mechanism for water-lubricated sliding. (C ) 1999 Elsevier Science S.A. All rights reserved.