Tetragonal fcc-Fe induced by κ-carbide precipitates: Atomic scale insights from correlative electron microscopy, atom probe tomography, and density functional theory

Correlative scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations resolve the correlation between elastic strain fields and local impurity concentrations on the atomic scale. The correlative approach is applied to coherent interfaces in a kappa-carbide strengthened low-density steel and establishes a tetragonal distortion of fcc-Fe. An interfacial roughness of similar to 1 nm and a localized carbon concentration gradient extending over similar to 2-3 nm is revealed, which originates from the mechano-chemical coupling between local strain and composition.