Investigation on Mg3Sb2/Mg2Si Heterogeneous Nucleation Interface Using Density Functional Theory.

Mingjie Wang,Hong Xu,Guowei Zhang,Yizheng Fu

doi:10.3390/ma13071681

Abstract

In this study, the cohesive energy, interfacial energy, electronic structure, and bonding of Mg2Si (111)/Mg3Sb2 (0001) were investigated by using the first-principles method based on density functional theory. Meanwhile, the mechanism of the Mg3Sb2 heterogeneous nucleation potency on Mg2Si grains was revealed. The results indicated that the Mg3Sb2 (0001) slab and the Mg2Si (111) slab achieved bulk-like characteristics when the atomic layers N ≥ 11, and the work of adhesion of the hollow-site (HCP) stacking structure (the interfacial Sb atom located on top of the Si atom in the second layer of Mg2Si) was larger than that of the other stacking structures. For the four HCP stacking structures, the Sb-terminated Mg3Sb2/Si-terminated Mg2Si interface with a hollow site showed the largest work of adhesion and the smallest interfacial energy, which implied the strongest stability among 12 different interface models. In addition, the difference in the charge density and the partial density of states indicated that the electronic structure of the Si-HCP-Sb interface presented a strong covalent, and the bonding of the Si-HCP-Mg interface and the Mg-HCP-Sb interface was a mixture of a covalent bond and a metallic bond, while the Mg-HCP-Mg interfacial bonding corresponded to metallicity. As a result, the Mg2Si was conducive to form a nucleus on the Sb-terminated-hollow-site Mg3Sb2 (0001) surface, and the Mg3Sb2 particles promoted the Mg2Si heterogeneous nucleation, which was consistent with the experimental expectations.

Highlights

Aluminium-magnesium-silicon alloys have shown considerable promise as the universal candidate materials for automotive and aerospace applications because of the formation of a Mg2 Si heterogeneous nucleus [1,2]
Mg2 Si (111)/Mg3 Sb2 (0001) interfaces were investigated through the density functional theory, which provides theoretical support for Mg3 Sb2 as the heterogeneous nucleation substrates of Mg2 Si grains, and which lays the theoretical foundation for the grain refinement of aluminium-magnesium alloys
The interfacial and surface properties of Mg2 Si (111)/Mg3 Sb2 (0001), such as surface energies, work of adhesion, and interfacial bonding energies, were implemented in the Cambridge serial total energy package (CASTEP) code based on the density functional theory [30,31]

Summary

Introduction

Aluminium-magnesium-silicon alloys have shown considerable promise as the universal candidate materials for automotive and aerospace applications because of the formation of a Mg2 Si heterogeneous nucleus [1,2]. It is understandable that Mg3 Sb2 may refine the size of Mg2 Si. The theoretical derivation of the interfacial properties and the interrelationships of phases at the interface based on density functional theory (DFT) has been widely used to predicate heterogeneous nucleation [21]. Theoretical estimates of heterogeneous nucleation between two solid interfaces have been mainly based on the Bramfitt mismatch theory [29], which elucidates that the smaller the mismatch of two heterogeneous lattice structures is, the smaller the interface energy is and the more effective the heterogeneous core growth is. Mg2 Si (111)/Mg3 Sb2 (0001) interfaces were investigated through the density functional theory, which provides theoretical support for Mg3 Sb2 as the heterogeneous nucleation substrates of Mg2 Si grains, and which lays the theoretical foundation for the grain refinement of aluminium-magnesium alloys. According to the equation of Bramfitt, the lattice mismatch of Mg2 Si (111)/Mg3 Sb2 (0001) is only 2.02%

Computational Methodology

Bulk Properties of Mg2 Si and Mg3 Sb2

Method

Electronic Structure and Bonding

Conclusions