Fabrication of composite ceramics of transition metal nitride and h-BN by pulse current pressure sintering

We tried to fabricate self-lubricant composite ceramics consisting of transition metal nitride (TiN or ZrN) matrixes and hexagonal boron nitride (h-BN) dispersions. Mixture powders were milled with a planetary ball mill for not more than 180 ks. Xray-diffraction patterns for the mixed powder showed that h-BN powder was finely grounded smaller than a submicron level and dispersed by the milling for longer than 36 ks. The pulse current pressure sintering (PCPS) method was employed to consolidate the mixed powders. Sintered compacts consolidated under the pressure of 80 MPa and 2073 K showed the highest density and hardness. The hardness of the sintered compacts decreased with the addition of BN of more than 5 mass%. This result suggests that the sintering of mixed powder could be strongly inhibited by the addition of h-BN. Relatively high density consolidation of more than 90% for single ZrN (or TiN) compact was obtained from the sintered compact of ZrN (or TiN) (or TiN) + 5mass% h-BN powders milled for 180 ks.