Abstract
We present a quantum-mechanical study of thermodynamic, structural, elastic, and magnetic properties of selected antiphase boundaries (APBs) in FeAl with the D0 crystal structure with and without Cr atoms. The computed APBs are sharp (not thermal), and they have {001} crystallographic orientation. They are characterized by a mutual shift of grains by 1/2〈100〉a where a is the lattice parameter of a cube-shaped 16-atom elementary cell of FeAl, i.e., they affect the next nearest neighbors (APB-NNN type, also called APB-D0). Regarding clean APBs in FeAl, the studied ones have only a very minor impact on the structural and magnetic properties, including local magnetic moments, and the APB energy is rather low, about 80 ± 25 mJ/m. Interestingly, they have a rather strong impact on the anisotropic (tensorial) elastic properties with the APB-induced change from a cubic symmetry to a tetragonal one, which is sensitively reflected by the directional dependence of linear compressibility. The Cr atoms have a strong impact on magnetic properties and a complex influence on the energetics of APBs. In particular, the Cr atoms in FeAl exhibit clustering tendencies even in the presence of APBs and cause a transition from a ferromagnetic (Cr-free FeAl) into a ferrimagnetic state. The Fe atoms with Cr atoms in their first coordination shell have their local atomic magnetic moments reduced. This reduction is synergically enhanced (to the point when Fe atoms are turned non-magnetic) when the influence of clustering of Cr atoms is combined with APBs, which offer specific atomic environments not existing in the APB-free bulk FeAl. The impact of Cr atoms on APB energies in FeAl is found to be ambiguous, including reduction, having a negligible influence or increasing APB energies depending on the local atomic configuration of Cr atoms, as well as their concentration.
Highlights
IntroductionAntiphase boundaries (APBs) are extended defects in crystals with multiple ordered sublattices
Antiphase boundaries (APBs) are extended defects in crystals with multiple ordered sublattices.They separate two mutually shifted regions of the same ordered phase
As the antiphase boundaries (APBs) energy typically depends on the crystallographic orientation of the interface only very weakly, we suppose that our choice of the {001} interface plane was sufficiently representative
Summary
Antiphase boundaries (APBs) are extended defects in crystals with multiple ordered sublattices. They separate two mutually shifted regions of the same ordered phase. The shift occurs during ordering processes, e.g., when different grains crystallize from different positions in the melt having a shifted origin defining their lattices. An APB is formed when two such domains meet and form an interface. As the formation of these interfaces occurs at elevated temperatures when diffusion and other thermal processes are active, an intermediate disordered phase can form (thermal APBs). Dislocations with Burgers vectors that are not translation vectors of the ordered superlattice can create APBs, as they move through an ordered phase (deformation APBs with sharp interfaces)
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