Temperature-Dependent Easy Slip System Transformation in WC and TiC

Owing to the distinguished mechanical properties, WC and TiC are important engineering materials used in machining and drilling. However, the hardness of WC and TiC is reduced dramatically under elevated temperatures, which therefore limits their application in high-temperature conditions. To reveal the reason for the decrease in hardness of WC and TiC, with the ultimate goal of designing potential hard materials, the temperature-dependent hardness of WC and TiC is investigated by a dislocation-based model. First, the possible dislocations were determined by generalized stacking fault energy distribution. Second, their temperature-dependent elastic constants were calculated, from which the stability and anisotropy were analyzed. WC and TiC are both stable up to 1500 K. The anisotropy of WC is increased with increasing temperature, while that of TiC is decreased. The anisotropy on different planes was also analyzed. Third, the slip system transformations were analyzed. The stress-dependent activation energy and temperature-dependent critical resolved shear stress of all dislocations decrease with increasing stress or temperature. The slip systems of single crystals and polycrystals are both changed with increasing temperature. The temperature-softening rate and yield strength of polycrystals are both between the minimum and maximum values of individual loading directions. Finally, the hardness of WC and TiC was calculated. They both decrease with increasing temperature. In addition, the influences of dislocation density and strain rate were also analyzed. The hardnesses of WC and TiC polycrystals are both decreased with increasing dislocation density. Up to 300 K, the hardness of WC is almost unchanged with increasing strain rate, while at higher temperature, it is increased with increasing strain rate. The hardness of TiC is increased with increasing strain rate. Our findings provide a vital reference for further research in the high-temperature hardness of transition metal carbides.