Fabrication and Properties of (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni Cermets

Abstract

Fine single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders were synthesized through the carbothermal reduction method. (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets were fabricated via vacuum sintering. Micrographs of powders and microstructures of the cermets were observed using transmission electron microscopy and scanning electron microscopy in combination with energy-dispersive spectroscopy. Phase compositions were investigated using x-ray diffraction. The C and N contents were measured using elemental analysis (CHNS/O). The optimized conditions for the synthesis process of single-phase (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders with high nitrogen content were 1500 °C for 2 h under a 2 kPa nitrogen atmosphere. Under such conditions, the particle size of the synthesized powder was less than 140 nm, and its carbon and nitrogen contents were 9.174 and 7.040 wt.%, respectively. The synthesized fine (Ti, W, Mo, Nb, Ta)(C, N) solid solution powders had a significant positive impact on the strengthening and hardening of Ti(C, N)-based cermets. The values of hardness and transverse rupture strength of the (Ti, W, Mo, Nb, Ta)(C, N)-Co-Ni cermets sintered at 1450 °C for 1 h in vacuum (SSC3) increase by 14.7 and 20.2% compared to those of traditional Ti(C, N)-WC-Mo2C-NbC-TaC-Co-Ni cermet (TC), respectively. However, the KIC value of SSC3 decreases by 14.1% compared to that of TC. The mechanism of strengthening and hardening and the cause of the low fracture toughness of the SSC were revealed by comparing the differences in the microstructures of SSC and TC.