Substitution behavior of Cu doped into Fe3Si and its effect on the electronic structure and mechanical properties based on first-principles calculation

The substitution behavior of Cu doped into Fe ₃Si and its effect on the electronic structure and mechanical properties of Fe ₃ Si were investigated using first principles plane-wave pseudopotential method based on density functional theory. Alloys with dopant Cu taking position of atoms Fe(I), Fe (II), and Si were labeled as Fe ₁₁CuSi ₄(I), Fe ₁₁CuSi ₄(II), and Fe ₁₂Si ₃ Cu, respectively. The calculated formation enthalpy and cohesive energy of the three compounds and Fe ₃Si alloy were all negative, indicating their thermodynamic stability. However, the atomic fraction of dopant Cu substituting on Si atom was approximately zero, implying that the formation of Fe ₁₂Si ₃ Cu is challenging. According to the analysis results of differential charge density and Bader charge, the covalent bond was weakened after Cu doping, while the ionic bond strength was in the order of Fe ₁₁CuSi ₄(I) > Fe ₃Si > Fe ₁₁CuSi ₄(II) > Fe ₁₂Si ₃Cu, which also indicated that the Fe ₁₂Si ₃Cu is less stable than the other three compounds. These results suggested that the dopant Cu atom preferred to substitute Fe atom, particularly Fe(I), but hardly substitute the Si atom. In order to gain a better understanding of the effect of Cu doping on the mechanical properties of Fe ₃ Si compound, the antiphase boundary energy (ABPE) and elastic constants of Fe ₃Si, Fe ₁₁CuSi ₄(I), and Fe ₁₁CuSi ₄(II) were further calculated. The value of APBE was decreased, whereas the plasticity of Fe ₃Si compound is increased with the substitution of Fe atoms by the Cu dopant. The enhanced plasticity of Fe ₃Si alloy by Cu doping results from the dominant influence of the reduced APBE and weakened covalent bonds over the effect of reduction in ionic bonding.