EFFECTS OF SURFACE PREPARATION ON THE FRICTION AND WEAR BEHAVIOR OF SILICON-NITRIDE SILICON-CARBIDE SLIDING PAIRS

Silicon carbide and silicon nitride specimens were fabricated to provide three different surface finishes. They were subjected to sphere-on-flat (pin-on-disc) testing in order to determine the interaction of load, velocity, disc surface finish, and material effects on unlubricated friction and wear. Tests were conducted in air using applied loads of 1 and 10 N, velocities of 0.1 and 0.5 ms-1, and surface preparations of 150-grit grinding, 220-grit grinding and fine polishing. The test duration was kept constant at 1000 m of sliding distance for the pin specimen. In half the tests silicon nitride was the pin material and silicon carbide was the disc material. For the other half, the pin and slider materials were reversed. There was a much greater effect of normal force on steady-state friction coefficient than of either surface finish or material pairing. Increasing the sliding velocity raised the friction coefficient for both material pairings and for all surface roughnesses. Higher wear resulted when the velocity increased, but the effect of surface finish on wear ranged from none in some cases to about a factor of 10 in other cases. A trend of increasing run-in period duration with increasing smoothness was observed. The results are interpreted in terms of material properties, the Lim and Ashby model, and the friction force-velocity product.