Friction coefficients and wear rates of MoS₂/Cu, BN/Cu composites

It is difficult to use an ordinary bearing in a vacuum and/or at a high temperature, because of evaporation or deterioration of the lubricant oil. A solid lubricant, M0S₂ or BN, is promising in such condition. Recently, a thin solid lubricant film is often applied on a hard material by PVD or CVD. The thin film is, however, easily removed when the load or friction speed is too high. On the other hand, when the lubricant is dispersed in a matrix, the solid lubricant always exists even the surface of the bearing is worn out. The aim of this experiment is to examine friction properties of the composites. Cu was plated on the lubricant particles by electroless deposition. The lubricant volume fraction (hereafter V_f) was up to 30 vol%. The Cu plated lubricant powder was hot-pressed to form composites at 873 K under 30 MPa in a vacuum. Friction properties of composites were determined by using a ball-on-disk type testing machine. The test was performed either in air or in a vacuum without oil at the room temperature. The coefficients of dynamical friction of the composites were decreased by the lubricant in the air. The effect of the lubricant was much remarkable in vacuum. The wear rates of the composites were, however, larger than Cu in the air. On the contrary, the wear rates of the composites were much less than one of Cu in a vacuum.