Impact of solutes on the lattice parameters and elastic stiffness coefficients of hcp Fe from first-principles calculations

The hexagonal close-packed (hcp) ε-martensite phase in steels nucleates from the γ-austenite parent phase and can undergo further transformation to the α′-martensite phase or exist as a metastable phase depending on temperature, mechanical loading, and alloy chemistry. The solute-dependent lattice parameters and elastic stiffness coefficients Cij of hcp Fe influence the mechanical properties of steels containing the ε-martensite phase, as well as the martensitic transformations between the phases. We use density functional theory to calculate the lattice parameters and Cij of single-crystal hcp Fe as functions of solute concentration in the dilute limit for the substitutional solutes Al, B, Cu, Mn, and Si, and the octahedral interstitial solutes C and N. Our computationally efficient methodology separates the solute dependence of the Cij into lattice strain and chemical bonding contributions. The computed data can be used to estimate the effect of solutes on polycrystalline elastic moduli and the strain energy associated with martensitic transformations. The data can also serve as inputs to microstructure-based models of multiphase steels containing the ε-martensite phase.