Ab Initio Study of the Effect of Al on the Solution Enthalpy of a Carbon Impurity in a Paramagnetic FCC Fe–Mn alloy

Abstract—The solution enthalpy of a carbon impurity in a paramagnetic Fe–Mn–Al alloy is calculated in terms of the density functional theory. To describe an Fe-based fcc alloys, we use a model, which takes into account the contribution of thermal magnetic fluctuations in a paramagnetic host with an atomic disorder and point defects. The addition of approximately 2 at % Al to an Fe–20 at % Mn is found to increase the enthalpy of solution of carbon relative to an Fe–Mn alloy and to decrease it relative to solution in γ-Fe. If an aluminum atom is located in the first coordination sphere of carbon, the interaction of Al and C atoms is shown to be repulsive because of the large deformation lattice distortion around an aluminum atom. The difference in the charge redistributions around an impurity in the absence and presence of an aluminum atom as the nearest neighbor is demonstrated. The influence of the local environment, lattice strain, and magnetic interactions on the energy of solution of carbon is analyzed.