Influence of Mo addition on microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in-situ carbothermal reduction of TiO2

Abstract

Series of Ti(C,N)-based cermets, with various amounts of Mo, are fabricated by in-situ carbothermal reduction of TiO2. SEM, TEM, XRD and EDS analysis are utilized to analyze the phase composition and microstructure of as-prepared cermets. The results reveal that the volume percentage of white-core grains in as-prepared cermets significantly larger than that in cermets fabricated by traditional methods. In addition, there are two types of white core/gray rim grains. One is the grains with bright white cores and the other is grains with offwhite cores. Mo plays an important role in the formation of rims and white cores. With increasing Mo addition, the rims of grains with white core tend to be complete and the rims of grains with black core become thinner. The volume percentage of grains with white core significantly increases due to the diffusion of Mo during solid-state sintering. Moreover, the dislocation formed in rim phase adjusts the misfit of rim/binder interface. As a result, the semi-coherent interface is observed in rim/binder interface of grains with black core. Overall, the cermet, with Mo content of 14 wt %, renders optimal mechanical properties, with fracture toughness (KIC) of 11.2 MPa m1/2, transverse rupture strength (TRS) of 2403 MPa and a hardness of 90.8 HRA.