Research On The Synthesis Of Fine Grained Ti(C, N)-based Cermets

The relationship among composition, manufacturing process, microstructure, post-treatment technique and properties of fine grained Ti(C,N)-based cermets has been researched by X-ray diffraction (XRD), scanning electron microscopy(SEM) and transmission electron microscopy (TEM), energy dispersive X-ray analysis(EDS), and electron-probe microanalysis (EPMA).The research development of Ti(C,N)-based cermets over recent years has been systematically overviewed at first, which includes the influence of composition, additive, manufacturing process on the microstructures and properties of Ti(C,N)-based cermets.The influence of sintering temperature and addition of nano-structured powders on the microstructure and performance of cermets has been studied. When nano-structured TiC and TiN powders accounted for 10wt% of all the amount of TiC and TiN, better mechanical properties were possessed by the sintered cermets. It was found that the grains without obvious rim phase and those with white-cores and black-shell increased greatly, and the volume proportion of metal binder decreased obviously. Some small grains were also found to be embedded in the rim phase of big grains and kept partially coherent with it. This strong combination between them and the reduction of the average size of particles enhanced the obdurability of the produced cermets.The changes of the surface microstructure and the surface hardness in the cermets heat-treated in normal pressure nitrogen have also been studied. When the cermets were treated at 1200℃, a 15μmdeep surface, enriched N and Ti was produced. The particle size in the hardened surface became fine, and the volume fraction of rim phase reduced greatly. As a result, the surface hardness of the cermets was improved greatly after heat-treated in nitrogen.With different add contents of Mo, the valence electron structure of the (Ti1-x,Mox)(C_0.8,N_0.2) carbonitrides was calculated. It was showed that the plasticity was reduced with the addition of Mo. With different add contents of Cr, the valence electron structure of (Ti_0.9-x,Mo_0.1,Cr_x)(C_0.8,N_0.2) carbonitrides was also calculated. When x=0.15,∑_{A + C + D +E}ⁿ was the smallest, and the plasticity of cermets was best. It has also been proved by the result of experiments that the plasticity of rim phase was improved by subtle addition of Cr₃C₂. As a result, the transverse rupture strength of Ti (C,N)-based cermets was enhanced greatly.