Ab initio calculations of the lattice parameter and elastic stiffness coefficients of bcc Fe with solutes

Abstract

Density functional theory calculates the effects of substitutional Al, B, Cu, Mn, Si solutes, and octahedral interstitial C and N solutes on the lattice parameter and elastic stiffness coefficients of bcc Fe at 0 K. We introduce a solute strain misfit tensor that quantifies how solutes change the lattice parameter. Solutes modify the elastic stiffness coefficients through these volumetric changes and by altering chemical bonds. We compute each of these contributions to the elastic stiffness coefficients separately, and verify that their sum closely agrees with changes in the elastic stiffness coefficients computed directly using fully optimized supercells with solutes. Computing the two elastic stiffness contributions separately is more computationally efficient and provides more information on solute effects than the direct calculations. Comparison with experimental data indicates that our approach accurately predicts solute-induced changes in the structural and elastic properties. The computed data can be used to quantify solute-induced changes in mechanical properties such as strength and ductility, and can be incorporated into higher length-scale models to improve their predictive capabilities.