Elastic properties of fcc Fe–Mn–X (X = Al, Si) alloys studied by theory and experiment

We have studied the influence of Al and Si additions on the elastic properties of face-centered cubic (fcc) Fe–Mn random alloys with Fe/Mn ratios of 4.00 and 2.33 using ab initio calculations. When Al is added up to 8 at.% the shearing elastic constants (C11–C12)/2 and C44 decrease, resulting in a drop of ∼20% in shear and ∼19% in Young’s modulus. In fcc Fe–Mn–Si alloys, the trends in the elastic constants are similar, but less drastic, with a ∼7% shear and ∼6% Young’s modulus decrease when Si is added up to 8 at.%. The Fe/Mn ratio exhibits a minor influence on the shear and Young’s modulus values at constant Al and Si contents. To assess the quality of the ab initio data Fe–Mn–Al and Fe–Mn–Si thin films with an fcc structure were combinatorially synthesized and the elastic properties measured using nanoindentation. For both systems the measured and calculated lattice parameters are in good agreement. Although the measured Young’s modulus data showed significant scatter due to the high surface roughness, they are in good agreement with the predicted values. For the Fe–Mn–Al system the calculations generally underestimate the experimental data by ∼15%. For the Fe–Mn–Si system the calculated data are in general lower by ∼10% than the experimentally determined values. The presented results are of relevance for multicomponent alloy design, since the effect of Si and Al addition on the elastic properties of Fe–Mn alloys can be predicted based on ab initio data.

Research highlights
► Elastic properties of fcc Fe–Mn–Al and Fe–Mn–Si alloys.
► Determination of elastic properties using ab initio calculations.
► DLM description of the magnetic state yields reasonable elastic properties predictions.
► Experimental validation using nanoindentation of combinatorial thin films.