Crystallographic Calculations and First-Principles Calculations of Heterogeneous Nucleation Potency of γ-Fe on La2O2S Particles

Rare earth (RE) inclusions with high melting points as heterogeneous nucleation in liquid steel have stimulated many recent studies. Evaluating the potency of RE inclusions as heterogeneous nucleation sites of the primary phase is still a challenge. In this work, the edge-to-edge matching (E2EM) model was employed to calculate the atomic matching mismatch and predict the orientation relationship between La2O2S and gamma-Fe from a crystallographic point of view. A rough orientation relationship (OR) was predicted with the minimum values of f(r)=9.43% and f(d)=20.72% as follows: [21 over bar 1 over bar 0]La2O2S & PAR;[100](gamma-Fe) and (0003 over bar )La2O2S & PAR;(002 over bar )(gamma-Fe). The interface energy and bonding characteristics between La2O2S and gamma-Fe were calculated on the atomic scale based on a crystallographic study using the first-principles calculation method. The calculations of the interface energy showed that the S-terminated and La(S)-terminated interface structures were more stable. The results of difference charge density, electron localization function (ELF), the Bader charges and the partial density of states (PDOS) study indicated that the La(S)-terminated interface possessed metallic bonds and ionic bonds, and the S-terminated interface exhibited metallic bond and covalent bond characteristics. This work addressed the stability and the characteristics of the La2O2S/gamma-Fe interface structure from the standpoint of crystallography and energetics, which provides an effective theoretical support to the study the heterogeneous nucleation mechanism. As a result, La2O2S particles are not an effective heterogeneous nucleation site for the gamma-Fe matrix from crystallography and energetics points of view.