Revealing the Local Microstates of Fe-Mn-Al Medium Entropy Alloy: A Comprehensive First-principles Study

Entropy-stabilized multi-component alloys have been considered to be prospective structural materials attributing to their impressive mechanical and functional properties. The local chemical complexions, microstates and configurational transformations are essential to reveal the structure-property relationship, thus, to promote the development of advanced multi-component alloys. In the present work, effects of local lattice distortion (LLD) and microstates of various configurations on the equilibrium volume (V-0), total energy, Fermi energy, magnetic moment (mu(Mag)) and electron work function (phi) and bonding structures of the Fe-Mn-Al medium entropy alloy (MEA) have been investigated comprehensively by first-principles calculations. It is found that the phi and mu(Mag) of those MEA are proportional to the V-0, which is dominated by lattice distortion. In terms of bonding charge density, both the strengthened clusters or the so-called short-range order structures and the weakly bonded spots or weak spots are characterized. While the presence of weakly bonded Al atoms implies a large LLD/mismatch, the Fe-Mn bonding pairs result in the formation of strengthened clusters, which dominate the local microstates and the configurational transitions. The variations of mu(Mag) are associated with the enhancement of the nearest neighbor magnetic Fe and Mn atoms, attributing to the LLD caused by Al atoms, the local changes in the electronic structures. This work provides an atomic and electronic insight into the microstate-dominated solid-solution strengthening mechanism of Fe-Mn-Al MEA.