Microstructural evolution and phase transition mechanism of Ti(C,N)-based cermets during vacuum sintering process

Abstract Ti(C,N)-based cermets were fabricated using section vacuum sintering. The density and shrinkage ratio of sintered samples were recorded and analyzed. Phase transition, microstructure and interface behaviors of cermets were examined by transmission electron microscope, X-ray diffractometer and scanning electron microscope. As the sintering temperature rising, the number of pores in cermets was decreased and the density of samples was increased. Moreover, with the progress of sintering, atoms of various elements were constantly diffusing and gathering, affecting the formation of different microstructure, and the angle and intensity of each XRD peak were also constantly changing slightly, or disappearing at a certain temperature. These relevant results indicated that the proportion of heavy element to Ti in the hard phase would affect its lattice parameter. After the appearance of liquid phase, the densification mechanism changed from surface diffusion to grain boundary diffusion, thus accelerating the densification. With the proceeding of sintering process, various microstructures were formed such as core - rim/rimless structure. Finally, the process of interface change in core rimless phase transition was discussed. This rim phase, formed in solid state sintering process while failing to develop into core-rim structure after liquid sintering, was formed by some heavy elements short-range diffusion into core phase. The orientation different and the misfit between this core and rim were relatively large. While after liquid sintering, the semi-coherency or even coherency state at the interface of core-rimless and binder was formed.