An advanced self-lubricating ceramic composite with the addition of core-shell structured h-BN@Ni powders

Aiming at the contradiction between tribological and mechanical properties of traditional self-lubricating ceramic composites, an advanced self-lubricating ceramic composite with the addition of pure-metal coated solid lubricant powders was developed in terms of microstructural modification of the traditional composites. Core-shell structured h-BN@Ni powders were synthesized by electroless plating technique with hydrazine hydrate as reducing agent. Al2O3/(W,Ti)C/h-BN@Ni composite made by adding h-BN@Ni powders exhibited notable improvements in microstructure and mechanical properties as compared with Al2O3/(W,Ti)C/h-BN composite made by adding uncoated h-BN powders. EDS and TEM analyses showed that the Ni shell particles in the Al2O3/(W,Ti)C/h-BN@Ni composite concentrated around the h-BN core grains and were located at grain boundaries or within the matrix grains. Due to their flaky structure, the h-BN grains had orientation distribution in the as-prepared ceramic composites, which resulted in anisotropies in mechanical properties and tribological behaviors. Dry sliding friction test revealed that the Al2O3/(W,Ti)C/h-BN@Ni composite had lower friction coefficient and higher wear resistance than the Al2O3/(W,Ti)C/h-BN composite. The different h-BN release modes caused tribological behaviors of the friction surface perpendicular to the hot pressing axis (HPA) to be better than those of the friction surface parallel to HPA.