Correlation analysis between microstructure and mechanical properties of spark-plasma-sintered Ti(C, N)-W cermets according to changes in titanium, carbon and nitrogen contents

In this study, TiC-50 wt% W, TiN-50 wt% W, TiC0.7N0.3-50 wt% W, Ti0.55C0.13N0.32-50 wt% W, TiC0.5N0.5-50 wt % W and TiC0.5N0.5-70 wt% W cermet specimens with grain sizes smaller than 1 mu m were prepared by blending TiC, TiN, TiC0.5N0.5, W and Ti powders followed by the spark plasma sintering of the blended powders. Under Ar gas flow conditions at 1973 K, the TiC0.5N0.5-50 wt% W and TiC-50 wt% W cermet specimens exhibited the first and second highest strengths, respectively, whereas the TiN-50 wt% W and Ti0.55C0.13N0.32-50 wt% W cermet specimens exhibited the lowest strength among all the cermet specimens prepared in this study. In contrast, the Ti0.55C0.13N0.32-50 wt% W and TiC0.5N0.5-50 wt% W cermet specimens exhibited the first and second highest strengths, respectively, at room temperature in laboratory air. Coherent interfaces, whose type differed from those of the TiC0.5N0.5-50 wt% W and TiC0.5N0.5-70 wt% W cermet specimens, were found in (Ti, W)C grains in the TiC-50 wt% W cermet specimen. The coherent interfaces in the TiC-50 wt% W cermet specimen were considered to suppress the grain growth because these interfaces normally suppress the interdiffusion of Ti, W and C atoms. Moreover, the grain growth seemed to be suppressed in the TiC0.7N0.3-50 wt% W, Ti0.55C0.13N0.32-50 wt% W, TiC0.5N0.5-50 wt% W and TiC0.5N0.5-70 wt% W cermet specimens owing to the core-rim structures with coherent interfaces in the cermet specimens. The coherent interfaces and core-rim structures are thus considered to contribute to improving the high -temperature strength of all the cermet specimens except for the TiN-50 wt% W cermet specimen, which contained neither core-rim structures nor coherent interfaces.