Studies of the Unlubricated Wear of a Commercial Cobalt-Base Alloy at Temperatures up to about 400 C

Abstract

Pins of a commercial cobalt-base alloy (Stellite 31) have been worn against disks of the same material at room temperature and at various externally-induced ambient temperatures between about 100 C and 400 C, under continuous and reciprocating sliding conditions without lubrication. An unexpected maximum in the wear rate versus ambient temperature curve occurred at about 200 C for specimens which had previously been exposed to ambient temperatures less than the temperature of any given experiment. For entirely new specimens, however, this maximum could not be detected, although there was a pronounced decrease in the wear rate at around 200 C. Friction coefficients, pin temperatures, surface topographies, and the compositions of the wear debris were determined for these experiments, and significant changes were also found to occur at disk temperatures around 200 C. The changes in wear, friction, temperature, wear debris composition, and surface topography around 200 C are discussed in terms of the onset of a mild wear mechanism in which the spinel oxides of chromium and cobalt are assigned important roles.