文摘
The phase stabilities of Mo\(_{1-x}\)Al\(_{x}\)N and Nb\(_{1-x}\)Al\(_{x}\)N \((x=0, 0.25, 0.5, 0.75, 1.0)\) with four possible WC, NiAs, B1 and B4 structures were investigated using first-principles methods. With the increase of Al contents, the most stable structure changes from WC (\(x=0\) and 0.25) to NiAs (\(x=0.5\)) structure. When \(x=0.75\) and 1.0, the most stable structure is B4. The elastic constants, Young’s modulus, shear modulus, bulk modulus and elastic anisotropy were calculated. Based on the Pugh criterion and Poisson’s ratio, the ductility and hardness of Mo\(_{1-x}\)Al\(_{x}\)N and Nb\(_{1-x}\)Al\(_{x}\)N were investigated. The ductility of Mo\(_{1-x}\)Al\(_{x}\)N decreases with the increase of Al contents. However, the ductility of Nb\(_{1-x}\)Al\(_{x}\)N enhances with the increase of Al contents. The density of states and charge density differences were used to analyze the mechanical properties. The results are in agreement with the predictions based on the Pugh criterion and Poisson’s ratio.