Effect of C content on the surface gradient structure of (Ti, Mo)(C, N) and Ti(C, N)-based cermets

The C content has a significant effect on the microstructure especially surface gradient structure of nitrogen-containing cermets. In the literature, how the C content affects the gradient structure of nitrogen-containing cermets is unclear. Combining thermodynamic calculations and experimental techniques, a series of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets with different carbon contents were investigated experimentally. When sintering in a denitrification atmosphere, the C content in the binder phase of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets shows the trend of high surface concentration and low core concentration, the thickness of Ni-rich gradient layer of cermets decreases with the increase of C content, and the (Mo, Ti)C phase precipitates in the gradient layer of Ti(C, N)–Mo2C–Ni cermet. The results of XRD and specific saturation magnetization data indicate a decrease of the solubility of alloy elements Ti and Mo in the Ni binder phase with the increase of C content. The formation mechanism of the gradient layer of (Ti, Mo)(C, N)–Ni and Ti(C, N)–Mo2C–Ni cermets at different C contents was discussed. Due to the thermodynamic coupling of Ti–C, the high concentration of C on the cermets surface inhibits the local activity of Ti atoms, weakens the driving force for migration of Ti to the core, and results in a thinner Ni-rich gradient layer. Moreover, the amalgamation and growth of hard particles in the alloy and the number of bright inclusions in (Ti, Mo)(C, N)-based cermets can also be reduced with the increase of C content.