First-principles study on the interfacial stability and electronic structure of MgAl2O4/α-Fe heterogeneous nucleation interface in Mg-treated steels

In this study, the orientation of the acicular ferrite (AF) nucleated on MgAl 2 O 4 inclusion in Mg-treated steel was explored via electron backscatter diffraction (EBSD). Subsequently, the MgAl 2 O 4 (100)/α-Fe(100) interface was investigated for its interfacial stability and electronic structure using the first-principles method. Fifteen interface configurations with different terminals and stacking sequences were constructed. The results showed that the orientation relationship between MgAl 2 O 4 and AF was as follows: { 100 } MgAl 2 O 4 ∥{100} AF , < 010 > MgAl 2 O 4 ∥< 011> AF and < 011 > MgAl 2 O 4 ∥< 010 > AF . The Mg/Fe-Hollow (H) and O/Fe-Hollow 2 (H₂) were the most stable configurations for the Mg and O terminated MgAl 2 O 4 (100)/α-Fe(100) interfaces. For the AlO₂ and AlO terminals, the O-top (T O ) stacking was the most stable stacking sequence for Fe atoms. Electronic structure analysis revealed that the Mg/Fe-H interface formed only weak Fe-Mg metallic bonds, resulting in the lowest adhesion work. The O/Fe-H₂, Al O ₂-T O and AlO/Fe-T O interfaces all exhibited Fe-O ionic and covalent bonds as a result of the orbital hybridization between Fe-3d and O-2p. Besides, metallic bonds also formed in these three interfaces. The covalency of Fe-O bonds formed in the O/Fe-H₂ interface was strongest, providing it the largest adhesion work. Among all the configurations, the lowest interfacial energy was observed for the O/Fe-H₂ interface under the Mg-rich condition, whereas the AlO₂-T O interface showed the lowest interfacial energy under the Al-rich condition. Within a large range of the chemical potential of Al, the interface energy was lower for both the O /Fe-H₂ and AlO₂-T O interfaces than γ-Fe/α-Fe, decreasing the energy for heterogeneous nucleation of AF on the surface of MgAl₂O₄.