Alloying effects on elastic properties of TiN-based nitrides

The effects of alloying (Cr, Zr, Nb, V, W, Mo and Al) on the trend of elastic properties of TiN-based nitrides have been investigated using ab initio density functional theory calculations within the generalized gradient approximation. The calculated elastic coefficients of pure TiN are in good agreement with experimental results and compare favourably with other theoretical calculations. The Cauchy pressure (C-12-C-44) and the ratio G/B of shear modulus (G) and bulk modulus (B) are used to assess the brittle/ductile behaviour of TiN accompanying alloying additions. The difference between C-44 and G/B or Cauchy pressure in evaluating the brittle/ductile behaviour of nitrides is identified. The results demonstrate that alloying with Mo and W can reduce G/B to near 0.5 and reverse Cauchy pressure from negative values to positive values. These results indicate that Mo and W could improve the ductility of TiN, with Mo achieving the best effect.