First-principles calculations of mechanical properties of TiC and TiN

Abstract First-principles calculations are performed to investigate the elastic properties and hardness of TiC and TiN. The calculated elastic constants for TiC agree closely with the experimental results. TiC is of nearly elastic isotropic characteristic according to its Zener's anisotropy parameter, A = 0.91, while the value for TiN, A = 0.8, shows its higher degree of elastic anisotropy relative to TiC. The ratios of bulk modulus (B) to shear modulus (G), 1.31 for TiC and 1.42 for TiN, indicate their brittle nature. The estimated hardness for TiC is consistent with the experimental values, whereas that for TiN is about 30% higher than the experimental ones. And the ultra high hardness for TiC and TiN may attribute to the interactions between Ti-3d and non-metal (C or N) 2p electrons according to the electronic structure analysis.