INFLUENCE OF TRIBOCHEMICAL REACTION-PRODUCTS ON FRICTION AND WEAR OF SILICON-NITRIDE AT ELEVATED-TEMPERATURES IN REACTIVE ENVIRONMENTS

Friction coefficients and wear rates of hot-pressed Si3N4 have been measured in a ball-on-flat linear-sliding geometry at temperatures ranging from room temperature to 1273 K in Ar and air containing up to 63% H2O. In inert environments, the friction coefficients (ranging between 0.6 and 0.7) are independent of temperature, and wear rates increase with temperature. In oxidizing environments, the friction and wear are reduced by the presence of tribochemical reaction products. Friction coefficients and wear rates are lowered when the wear debris spontaneously forms into rolls, oriented perpendicular to the direction of relative motion, at high H2O levels in the temperature range of 873 to 1073 K.