Characterization of phase transformation and microstructure of nano hard phase Ti(C,N)-based cermet by spark plasma sintering

By means of optical microscope , scanning electron microscope （SEM） and transmission electron microscope （TEM）, the process of densification, the characterization of phase transformation and the microstructure for spark plasma sintering （SPS） nano hard phase Ti（C,N）-based cermet were investigated. It is found that the spark plasma sintering （SPS） enables the nano hard phase Ti（C,N）-based cermet to densify rapidly, however, the full densification of the sintered samples can not be obtained. The rate of phase transformation is significantly quick. When being sintered at 1 200 ℃ for 8 min, Mo2C is completely dissolved, and TiN dissolves into TiC entirely and disappears. Above 1 200 ℃, Ti（C,N） begins to decompose and the atoms of C and N separate from Ti（C,N） resulting in the generation of N2 and the graphite. Due to the denitrification and the graphitization, the density and the hardness of sintered samples are rather low. The distribution of grain size of the sample sintered at 1 350 ℃ covers a wide range of 90500 nm, and most of the grain size are about 200 nm. The hard phase is not of typical core-rim structure. Oxides on the surface of particles can not be fully removed and present in sample as titanium oxide TiO2. Graphite exists in band-like shape.