Stability, electronic structures, and mechanical properties of Fe-Mn-Al system from first-principles calculations

The stability, electronic structures, and mechanical properties of the Fe-Mn-Al system were determined by first-principles calculations. The formation enthalpy and cohesive energy of these Fe-Mn-Al alloys are negative and show that the alloys are thermodynamically stable. Fe₃Al, with the lowest formation enthalpy, is the most stable compound in the Fe-Mn-Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe-Mn-Al alloys were analyzed. The bonding characteristics of these Fe-Mn-Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt-Reuss-Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe_2.5Mn_0.5Al has the highest bulk modulus, 234.5 GPa. Fe_1.5Mn_1.5Al has the highest shear modulus and Young's modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe-Mn-Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young's modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe-Mn-Al alloys were explored.