Fracture behaviors of Ti(C, N)-based cermets with different contents of metal binder

Ti(C0.7,N0.3)-Mo2C–Ni cermets are fabricated by powder metallurgy methods. We systematically investigate the microstructure, fracture morphology, crack propagation mechanism, and interface characteristics of Ti(C, N)-based cermets with different Ni binder contents.The increased dissolution of carbides and carbonitrides leads to a large amount of (Mo,Ti)(C,N) solid solution precipitates, which then spontaneously nucleate, resulting in a significant increase in the content of white core-gray rim grains in the cermets with a high binder content. The increased Ni binder largely improves the flexural strength and fracture toughness of the Ti(C,N)-based cermets because of the ductile dispersion toughening. The rim-core interfaces have a superior atomic coherent relationship in all Ti(C,N)-based cermets owing to the small lattice mismatch. The lattice mismatch of the interface between the rim phase and metal binder is remarkably decreased with the increase in the binder content to construct an atomic coherent relationship. Thus, the increased Ni binder promotes atomic ordering at the interface between the ceramic grains and binder and strengthens the grain boundary. The characteristic (111) peak of nickel shifts to a larger angle due to the reduction in the Ni-based solid solution lattice distortion. Therefore, the effect of solid solution strengthening is diminished with the increase in binder content, which results in a decreased binder strength. In the Ti(C,N)-based cermets with low metal binder contents, the fracture of the grain boundary between the ceramic grains and binder is the predominant failure mechanism. The intergranular crack accompanied by crack branching is the main characteristic of crack propagation. A hybrid fracture mode of intergranular and transgranular cracks is observed in the Ti(C,N)-based cermets with a moderate binder content. As the binder content further increases, the plastic yield deformation and subsequent tearing of the metal binder are the main fracture characteristics because of grain boundary strengthening and decreased strength of the binder.