Effect of the green state on the sintering of Ti(C,N)-based cermets

Different types of compaction process were employed in studying the effect of the green state on the sintering of TiC-TiN-Ni-Mo2C and Ti(C0.3N0.7)-Ni-Mo2C cermets. Specimens of 51 mm x 7 mm x 5 mm with and without 5 wt% polyethylene glycol (Carbowax) were uniaxially pressed at 150 MPa, some being subsequently compacted by cold isostatic pressing (CIP) at 350 MPa. Liquid-phase sintering was carried out in nitrogen atmosphere at temperatures of 1500 and 1530 degrees C for 2 h. Solid-state sintering was performed also at 1450 degrees C for comparison. It is shown that 1450 degrees C is too low a temperature for effective sintering no matter what compaction method is used. The green-state porosity and the pore-size distributions, as sintered morphologies, and the microhardness and microstructural development were characterized. Mercury-porosimetry measurements indicate that with increasing compacting pressure, large pores are eliminated and the pore-size-distribution curves shift towards smaller pores. Higher compaction load also leads to a decrease in average pore size and a wider pore-size distribution. It was found that the Ti(C0.3N0.7)Ni-Mo2C cermets are superior to the TiC-TiN-Ni-Mo2C cermet, in that they possess better micro-hardness, higher bulk density and a lower porosity level. Cermets with Carbowax additives are sinter better than those without. In comparison of the different compaction processes, the two-stage consolidation (die-pressing + CIP) results in better sintering properties than does die-pressing alone