First-Principles Prediction of Incipient Order in Arbitrary High-Entropy Alloys: Exemplified in Ti 0.25CrFeNiAl x
23 Pages Posted: 4 Dec 2019 Publication Status: Accepted
Abstract
Multi-component solid-solution alloys, including high-entropy alloys, experience segregation or partially-ordering as they are cooled to lower temperatures. For Ti0.25CrFeNiAlx, experiments suggest a partially-ordered B2 phase, whereas CALculation of PHAse Diagrams (CALPHAD) predicts a region of L21+B2 coexistence. We employ first-principles KKR-CPA electronic-structure to assess stability of phases with arbitrary order having a specific Bravais lattice and composition, as it handles chemical disorder by direct configurational averaging during density-functional theory charge self-consistency. In addition, KKR-CPA linear-response theory is used to predict atomic short-range order (SRO) in the disorder phase, which reveals potentially competing long-range ordered (LRO) phases. With Warren-Cowley pair correlations defined relative to the diffraction lattice, SRO can be analyzed by concentration-waves (site-occupation probabilities) for any partially-ordered cells (including estimated energy gains) that can then be assess directly by KKR-CPA calculations. Our results are in good agreement with experiments and CALPHAD in Al-poor regions (x ≤0.75) and with CALPHAD in Al-rich region ($0.75 ≤x≤1), and they suggest more careful experiments in Al-rich region are needed. Our first-principles KKR-CPA electronic-structure and SRO predictions with additional concentration-wave analysis are shown to be a powerful and fast method to identify and assess competing phases in complex solid-solution alloys.
Keywords: Density-functional theory, high-entropy alloy, short-range order, concentration-waves, order-disorder
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