Gebhardt, T: Ab initio lattice stability and elastic propert

and magnetic effects on the elastic properties of fcc Fe-Mn based alloys was investigated using a combined theoretical and experimental research strategy. In a first step, binary Fe-Mn thin films with a graded chemical composition were synthesized. Nanoindentation experiments were carried out to investigate the elastic properties as a function of the Mn content. As the Mn content increases from ~ 23 to ~ 39 at.-%, the average bulk modulus varies from 143 to 105 GPa. Ab initio calculations served to evaluate magnetic effects on the elastic properties. The magnetic state description with disordered local moments yields the best agreement with the experimental results, whereas with nonmagnetic and antiferromagnetic (AFM) configurations the bulk modulus is overestimated. The strong impact of the magnetic configuration may be understood based on the differences in the chemical bonding and the magnetovolume effect. It is suggested that due to minute energy differences of competing AFM configurations, a mixture of these with a "notional magnetic disorder" is present, which can in fact be well described by the disordered local moments model. Furthermore, the influence of Al and Si additions on the elastic properties of fcc Fe-Mn random alloys with Fe/Mn ratios of 4.00 and 2.33 was evaluated 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 ab initio data, Fe-Mn-Al and Fe-Mn-Si thin films with an fcc structure were combinatorially synthesized and the elastic properties were measured using nanoindentation. For both systems the measured and calculated lattice parameters are in good agreement. Although the measured Young's modulus data scatter significantly due to large surface roughness, they are in good agreement with the predictions. For the Fe-Mn-Al system the calculations generally underestimate the experimental data by ~ 15 %. With respect to the Fe-Mn-Si system, the calculation data are in general by ~ 10 % lower than the experimentally determined values, indicating that the effect of Si and Al additions on the elastic properties of Fe-Mn alloys can be predicted based on ab initio data. The presented results are of relevance for multicomponent alloy design.