First-principles investigations on the elastic properties, thermodynamic properties, electronic structures and anisotropy sound velocity of AlTi3N, AlTi2N, AlTi4N3 and Al2Ti3N2 ternary nitrides

Abstract

Al-Ti-N nitrides have drawn much more interest in recent years. The study used first-principles calculations within density functional theory (DFT) to investigate the physical properties of AlTi₃N, AlTi₂N, AlTi₄N₃ and Al₂Ti₃N₂ ternary nitrides. We demonstrated the thermodynamic stability and mechanical stability of AlTi₄N₃, AlTi₂N, AlTi₃N and Al₂Ti₃N₂ by the formation enthalpies and elastic constants. According to Poisson's ratio, AlTi₃N (0.387) and Al₂Ti₃N₂ (0.307) are ductile, AlTi₂N (0.236) and AlTi₄N₃ (0.135) are brittle. The most anisotropic phase is AlTi₄N₃, as evidenced by the two-dimensional projection of bulk, shear and Young's modulus and the 3D surface structures. The anisotropy order is as follows: AlTi₄N₃ > AlTi₃N > Al₂Ti₃N₂ > AlTi₂N. The hardness of AlTi₂N is 15.74GPa, which is the highest among the four nitrides. The hardness of AlTi₃N is the lowest, which is 2.38 GPa. Moreover, from the Debye temperature, AlTi₂N has the highest Debye temperature, indicating the strongest bond strength and highest hardness. The Gibbs free energy of the material is negatively correlated with temperature. Among these nitrides, Al₂Ti₃N₂ has the smallest Gibbs free energy and has excellent formation ability.