Solid/liquid lubrication of ceramics at elevated temperatures

Abstract

This study investigates the effects of solid and liquid lubrication on the friction and wear performance of silicon nitride (Si 3N 4) and gray cast iron. The solid lubricant was a thin silver film (∼ 2 μm thick) produced on Si 3N 4 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°C. Without the silver films, the friction coefficients of Si 3 N 4 Si 3 N 4 test pairs were 0.05–0.14, and the average wear rates of Si 3N 4 pins were ∼5 × 10 −8 mm 3 N −1 m −1. The friction coefficients of Si 3N 4/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 ∼3 × 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 3N 4 pins and silver-coated Si 3N 4 disks was so low that it was difficult to assess by a surface profilometer. The wear rates of cast iron pins were ∼7 × 10 −9 mm 3 N −1 m −1 up to 250°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.