Solid/liquid lubrication of ceramics at elevated temperatures

This study investigates the effects of solid and liquid lubrication on the friction and wear performance of silicon nitride (Si3N4) and gray cast iron. The solid lubricant was a thin silver film (similar to 2 mu m thick) produced on Si3N4 by ion-beam-assisted deposition. A high-temperature polyol-ester-base synthetic oil served as the liquid lubricant. Friction and wear tests were performed with pin-on-disk and oscillating-slider wear test machines at temperatures up to 300 degrees C. Without the silver films, the friction coefficients of Si3N4/Si3N4 test pairs were 0.05-0.14, and the average wear rates of Si3N4 pins were similar to 5 x 10(-8) mm(3) N-1 m(-1). The friction coefficients of Si3N4/cast iron test pairs ranged from 0.08 to 0.11, depending on test temperature. The average specific wear rates of cast iron pins were similar to 3 X 10(-7) mm(3) N-1 m(-1). However, simultaneous use of the solid-lubricant silver and synthetic oil on the sliding surfaces reduced friction coefficients to 0.02-0.08. Moreover, the wear of Si,N, pins and silver-coated Si,N, disks was so low that it was difficult to assess by a surface profilometer. The wear rates of cast iron pins were similar to 7 x 10(-9) mm(3) N-1 m(-1) up to 250 degrees C, but showed a tendency to increase slightly at higher temperatures. In general, the test results demonstrated that the solid/liquid lubrication of ceramic and/or metallic components is both feasible and effective in controlling friction and wear. (C) 1997 Elsevier Science S.A.