Influence of Mo addition on the microstructure and mechanical properties of TiC-NiTi cermets

TiC0.7 cermets with 20 vol% NiTi binder, containing up to 1.8 vol% Mo, were prepared by pressureless liquid-phase sintering at 1380 °C for 60 min. The pore size, apparent porosity, TiC grain size and binder mean free path length decreased with increasing Mo content up to 1.2 vol%. Further increasing the Mo content to 1.8 vol% resulted in a MoTi phase formation. Upon Mo addition, the carbides obtained a core-rim structure with dissolved Mo in the rim. The Mo distribution in the carbide and binder phases of the TiC0.7-NiTi and TiC-Ni cermets was correlated with the calculated Ti-Mo-C and Ti-Mo-Ni phase diagrams. The hardness significantly increased with increasing Mo addition up to 1.2 vol% and saturated upon further increasing the Mo content, while the bending strength remained almost the same. The E-modulus increased with increasing Mo addition up to 1.8 vol%, whereas the fracture toughness decreased.