Elastic anisotropies, thermal conductivities and tensile properties of MAX phases Zr2AlC and Zr2AlN: A first-principles calculation

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In this study, the mechanical stability, elastic properties, including single-crystal elastic constants, polycrystalline elastic modulus and elastic anisotropy, Debye temperatures, electronic properties, minimum thermal conductivities and tensile character of Zr 2 AlC and Zr 2 AlN were calculated by first-principles calculations based on density functional theory. The results showed that Zr 2 AlX (X = C, N) are mechanically stable and anisotropic in elastic properties, and the degree of elastic anisotropy of Zr 2 AlN is slightly greater than Zr 2 AlC, and the sound velocities and minimum thermal conductivities of Zr 2 AlC and Zr 2 AlN along the [001] and [100] directions are also anisotropic. Moreover, the density of states (DOS) and charge density difference distributions showed that these Zr 2 AlX have metallic-covalent-ionic mixed bonds. Finally, the calculated tensile properties along the [001] and [110] directions of these MAX phases showed that the tensile strength along the [110] direction is greater than that along the [001] direction. • The hardness and shear capacity are in a sequence of Zr 2 AlN > Zr 2 AlC. • Zr 2 AlC and Zr 2 AlN are anisotropic in elastic modulus and tensile strength. • Zr 2 AlN has the higher [001]-direction and lower [110]-direction tensile strength. • The formation enthalpies of competitive phases in Zr–Al–X system are calculated.