Structural stabilities and thermal properties of η′ Mg2Zn5-xAl2+x and η-MgZn2 phase in Al-Zn-Mg alloy: first-principles calculation and quasi- harmonic Debye approximation

The structural stabilities and thermal properties of eta' and eta phase at high temperature and pressure were investigated via first principles calculations combined with quasi-harmonic Debye approximation (QHA). The calculated results illustrate eta' possess high formation enthalpy with lower structural stability at high temperature, which may transits to equilibrium phase eta at temperature range of 510-520 K. The calculated thermodynamic properties indicate eta exhibits better thermal stability than eta' at high temperature. The thermoelastic properties of eta' and eta were estimated based on the temperature-dependent elastic constants C-ij(T), and it is revealed the elastic moduli of eta' are larger than that of eta though both two phases become deformable with elevated temperature. Moreover, the evaluated thermoelastic anisotropies suggest eta' and eta are essentially elastic isotropic on {0001} plane, while eta' exhibit serious mechanical anisotropy and angular bonding characters on both {10-10} and {01-10} planes at high temperature. (C) 2020 The Authors. Published by Elsevier B.V.

Automated summary

The structural stabilities and thermal properties of eta' and eta phases were investigated at high temperature and pressure using first principles calculations and quasi-harmonic Debye approximation. It was found that eta' has higher formation enthalpy but lower structural stability at high temperature, possibly transitioning to the equilibrium phase eta within a specific temperature range. In terms of thermoelastic properties, eta exhibits better thermal stability than eta' at high temperature, with eta' showing higher elastic moduli despite both phases becoming deformable with increased temperature. Thermoelastic anisotropies also suggest differences in mechanical characteristics between eta' and eta on different crystal planes at high temperature.