Evaluations of the Adsorption Polymerization Mechanisms of MgAl2O4–Ti2O3 Complex Inclusions in Steel

Research on intragranular acicular ferrite inclusions has demonstrated that high-melting-point oxide MgAl₂O₄ cores and composite inclusions precipitated by Ti₂O₃ adhesion can be used as effective nucleation particles in oxide metallurgy. However, the microscopic mechanism underlying this adsorption behavior remains unclear. Hence, in this study, the adsorption and polymerization mechanisms of Ti₂O₃ on the MgAl₂O₄(100)Mg- and MgAl₂O₄(111)O₃(Mg)-terminal surfaces in steel were studied using first-principles calculations based on density functional theory. The calculation based on the first principles of DFT and performed by the CASTEP code under plane wave basis set. The exchange correlation energy and correlation effects were described by generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof (PBE) function. Spin polarization was considered in all calculation. Ultrasoft pseudopotentials (USPP) was employed to describe the electron-ion interactions. The energy cutoff for the plane wave basis was set at 620 eV in the current work. For the Brillouin zone sampling, we carried out 3 × 3 × 3 k-points mesh for MgAl₂O₄ bulk using the method of Monkhorst-Pack. A vacuum layer of 20.0 Å is added above the top surface of MgAl₂O₄ to eliminate the interaction of the normal periodic repetition of the surfaces. In all the surface calculations, the use of symmetry in bulk crystal was failed and k-point grids is set to 3 × 3 × 1. The results of this study revealed that when the most stable adsorption positions of Ti₂O₃ on the surface of MgAl₂O₄(100)Mg- and MgAl₂O₄(111)O₃(Mg)-terminal are located at T_Al and F_Mg, the adsorption energy is the highest and the most stable. The most stable adsorption configurations are located on vertical and parallel (P1) surfaces. Through comparative analysis, the best surface for Ti₂O₃ adsorption was found to be the MgAl₂O₄(111)O₃(Mg)-terminal surface, and the adsorption behavior mainly occurred on the first layer of atoms on the surface. The best adsorption configuration was P1, and the best adsorption mode occurred when Ti₂O₃ formed three rings connected in pairs with the surface and embedded in the surface of the MgAl₂O₄(111)O₃(Mg)-terminal. This study provides insights into the adsorption polymerization mechanisms of MgAl₂O₄–Ti₂O₃ complex inclusions in steel that could facilitate the fabrication of novel low-melting-point oxides and sulfides.