FIRST-PRINCIPLES CALCULATION OF ELECTRONIC STRUCTURE AND ELASTIC PROPERTY OF AB 2 TYPE INTERMETALLICS IN Mg-Zn-Ca ALLOY

Abstract

Electronic structure and elastic properties of Mg2Sn, Mg2Ca and MgZn2 phases were investigated by means of first-principles calculations from CASTEP program based on density func- tional theory (DFT). The calculated lattice parameters were in good agreement with the experimental and literature values. The calculated heats of formation and cohesive energies show that Mg2Sn has the strongest alloying ability and structural stability. The density of states (DOS) of Mg2Sn, Mg2Ca and MgZn2 phases were calculated to analyze the mechanism of structural stability and mechanical properties. The calculated band structures show that Mg2Sn phase has the widest bandgap. The electron density difference indicate that bonding characteristics of Mg2Sn, Mg2Ca and MgZn2 phases were all covalent bond, ionic bond and metallic bond. The elastic constants of Mg2Sn, Mg2Ca and MgZn2 phases are calculated, the bulk moduli, shear moduli, Young's moduli and Poisson's ratio are then derived. Bulk moduli is assumed to be the ability of material resistance to volume change by applied stress, the larger bulk modulus of MgZn2 phase shows that it has stronger ability to resist deformation. Shear moduli is a measure of resistance to shear strain deformation under the deforma- tion condition of shear stress, the larger shear moduli value of Mg2Sn phase indicates that it has the stronger ability to resist shear strain deformation. The calculated Poisson's ration shows that MgZn2 has the largest value, and then followed by Mg2Ca and Mg2Sn. Hence, the plasticity of MgZn2 phase is the best. The calculated Young's moduli of Mg2Sn phase has the largest value and MgZn2 phase