Influence of Mo contents on microstructures and mechanical properties of (Ti,W,Mo)(CN)–Ni cermets

Abstract

Abstract The introduction of N2 gas during a sintering and carbothermal reduction process causes the separation of the WC phase in (Ti,W)(CN)–Ni cermet. Furthermore, the addition of secondary transition-metal carbides such as Mo2C, VC, and TaC not only promotes phase separation but also controls grain growth by the differences in their thermodynamic stabilities. Increased N2 flow during sintering increases the precipitation and coalescence of WC particles. The addition of Mo2C of 0.05\u202fmol fraction suppresses the precipitation and coalescence of WC. However, increases in both secondary carbides by >\u202f0.05\u202fmol fraction and the N2 flow by >\u202f4 kPa (≒ 30\u202fTorr), respectively, induces significant grain growth by coalescence. Consequently, the pore levels, hardness, and fracture toughness of the specimens are substantially affected by changes in the precipitation and grain growth behaviors of the WC particles. The fracture toughness of a (Ti0.7-xW0.3Mox)(C0.7N0.3)–20Ni cermet, sintered under 1.33 kPa (≒ 10\u202fTorr) N2, is significantly enhanced from 9 to 14\u202fMPa\u202fm0.5 by crack bridging and deflection.