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, TiC _0.7N _0.3–50 wt% W, Ti _0.55C _0.13N _0.32–50 wt% W, TiC _0.5N _0.5–50 wt% W and TiC _0.5N _0.5 –70 wt% W cermet specimens with grain sizes smaller than 1 μm were prepared by blending TiC, TiN, TiC _0.5N _0.5 , W and Ti powders followed by the spark plasma sintering of the blended powders. Under Ar gas flow conditions at 1973 K, the TiC _0.5N _0.5 –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 Ti _0.55C _0.13N _0.32–50 wt% W cermet specimens exhibited the lowest strength among all the cermet specimens prepared in this study. In contrast, the Ti _0.55C _0.13N _0.32–50 wt% W and TiC _0.5N _0.5–50 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 TiC _0.5N _0.5–50 wt% W and TiC _0.5N _0.5 –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 TiC _0.7N _0.3–50 wt% W, Ti _0.55C _0.13N _0.32–50 wt% W, TiC _0.5N _0.5–50 wt% W and TiC _0.5N _0.5–70 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.