Microstructural evolution in the phase mixtures of Ti(C,N)–Mo at 1600°C

The microstructural evolution occurring during sintering at 1600°C in two different phase mixtures of Ti(C,N) and Mo was studied. The mixture of Ti(C,N)–Mo (I) was prepared using as-received commercial powders of Ti(C,N) (particle size, 1.5–10 μm) and Mo2C (1.5–2.5 μm), and Ti(C,N)–Mo (II) using wet ball-milled powders of Ti(C,N) (0.2–1.5 μm) and Mo2C (0.2–1.5 μm), followed by a decomposition treatment of Mo2C to Mo. It was shown that, in both mixtures studied, most Mo atoms remained as an independent phase component even after 40 h at 1600°C. During the sintering treatment, particles of Mo were transformed into a coating of Mo around the Ti(C,N) particles via surface/boundary diffusion. No (Ti,Mo)(C,N) rim structure could be detected. The present results showed that there is hardly any inter-diffusion and reaction between Mo and Ti(C,N) at high temperatures. The diffusion mechanism therefore cannot be responsible for the formation of mixed carbide or carbonitride rims during the sintering of Ti(C,N)-based cermets.