Toughness, besides hardness, is one of the most important properties of wear-resistant coatings. We use ab initio density-functional theory calculations to investigate the mechanical properties of ternary metal nitrides Ti x M 1−x N, with M = Mo and W, for x = 0.5. Results show that Mo and W alloying significantly enhances the toughness of TiN. The electronic mechanism responsible for this improvement, as revealed by electronic structure calculations, stems from the changes in charge density

more »

... uced by the additional transition-metal atom. This leads to the formation of a layered electronic arrangement, characterized by strong, respectively, weak, directional bonding, which enables a selective response to strain, respectively, shear, deformations of the structures and yields up to 60% decrease in C 44 values.