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

Abstract

Yttria stabilised tetragonal zirconia polycrystal (YTZP) pins were subjected 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 lathe. Experiments were conducted under water-lubricated and unlubricated conditions. Wear rates of the pin were measured by mass loss. Under water-lubricated conditions, the wear rate was extremely geometry-dependent and the alignment of the polished pin determined the amount of wear, causing scatter in the results of nominally identical tests. Under dry conditions, an order of magnitude higher wear rate of the pin was observed. Under water-lubricated conditions, no wear was measured for pins that were polished flat in situ on the rig, suggesting that hydrodynamic lubrication was achieved. Higher 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 general smoothing of the surface. Scanning electron microscopy was used to examine the sliding surfaces and elucidate likely wear mechanisms. This technique revealed a milder YTZP wear mechanism for water-lubricated sliding.