Effects of elevated temperatures and topographies of worn surfaces on friction and wear of ceramics in vacuum

Abstract

Friction and wear tests were carried out with an Si 3N 4 pin and five kinds of ceramic disks at elevated temperatures (25°C∼600°C) in vacuum (5.8×10 −3 Pa) under a normal load of 6.02 N and a sliding speed of 0.2 m/s. For each test, the extent of damages on sliding worn surfaces, the wear rate and the friction coefficient were measured. Moreover, analysing the various parameters of the worn surface topographies, the change from mild wear to severe wear and the existence of the critical temperatures T c for each combination could be evaluated by using the topographical parameters and the ratio α b of the volume removed as wear debris to a volume of microgroove. The following results could be drawn: (1) The wear conditions changed from mild wear (wear rates≤10 −9 mm 2/N) to severe wear (wear rates≥10 −8 mm 2/N) at the critical temperatures T c which increased according to the order of Si 3N 4<SiC<TiC≈ZrO 2<Al 2O 3. (2) The wear rates of a pin and a disk increased with increase in the mean depth of microgrooves and in the depth of mean line, and with a decrease in the mean tip radius of protrusions generated during wear process. (3) When the relationships between the ratio α b, the tangent of the mean slope angle of protrusions, the mean flow pressure and the mean depth of microgrooves were obtained experimentally, the wear rates can be estimated quantitatively from the those mean depth values measured on a worn surface for the both wear conditions.