First-principles study of Mn alloying into Fe₃AlC: Towards the improvement of ductility

The first-principle calculations based on density functional theory (DFT) have been used to investigate structural and mechanical properties of Fe_24-xAl₈C₈Mn_x alloys. The calculated lattice constants of Fe₃AlC were in accord with experimental values, and its lattice deformation increased with the doped content of Mn increasing. The calculated formation enthalpy indicated that Mn atom is more likely to locate in the center of each face of the Fe₃AlC crystal lattice, and the Fe_24-xAl₈C₈Mn_x is a stable compound. The effect of Mn atoms on the independent elastic constants and the polycrystalline elastic parameters were calculated and discussed, such as bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν, anisotropy value A and Vickers hardness Hv. The effect of Mn content on the melting temperature of the Fe₃AlC alloys was also investigated, which represents the high temperature property. In addition, the density of states, the electron density difference, the population analysis and magnetic moment were also calculated to explain the mechanism of the structural stability, the chemical bonding and magnetization mechanism for the Fe₃AlC and the Fe_24-xAl₈C₈Mn_x alloys at the electron level.