The study of the boundary lubrication mechanism of BN-C-silicone oil composite colloid at high temperature

Nano-scale BN-C-silicone oil composite colloid was prepared in a planetary ball mill by using wet grinding techniques. Frictional experiments with GCr15 and 35CrMo as frictional pairs were then conducted under a wide range of temperature (from ambient temperature to 300 degrees C) on a pin-plate friction and wear tester. Results show that lubricating properties of the colloid were improved significantly. In particular, the frictional coefficient of the colloid is lower than that of the pure silicone oil at both ambient temperature and high temperature. For example, at ambient temperature, the frictional coefficients (f) of the BN-C-silicone oil composite colloid and pure silicone oil are about 0.05 and 0.18, respectively; while at 300 degrees C, the f value of the BN-C-silicone oil composite colloid and pure silicone oil are about 0.13 and 0.36, respectively. The characteristic of the worn surface film was also investigated by using SEM. SEM images show that on the worn surface, the concave zone is filled with some nano BN-C particles; while the rest of the particles are dispersed in the surface film. Therefore, BN-C particles may repair the worn surface, which tend to improve the boundary lubricity of the silicone oil. Finally, based on the model proposed by T.A.Stolarski, the rupture ratio of the lubricating film was discussed to address why BN-C-silicone oil composite colloid has relatively lower frictional coefficient even at high temperature.