Chemical short range order strengthening in a model FCC high entropy alloy

In order to understand the role of chemical short-range order on deformation mechanisms in FCC compositionally complex alloys, a random model alloy (Co30-Fe16.67-Ni36.67-Ti16.67) is annealed at various temperatures using Hybrid Molecular-dynamics/Monte-Carlo simulations. The simulations produce significant chemical short-range order (CSRO) that increases with decreasing annealing temperature. Annealing tends to homogenize regions of high enthalpy due to: (1) chemical species redistributing into more compact configurations, and (2) pairs of atoms forming chemical bonds that lower the overall energy of the system; the composition explored here shows significant amount of ordering in Ti-Fe pairs with respect to random distributions as described by pairwise (EAM) potentials due to Johnson and Zhou. An energy topology approach is used to assess the local strengthening behavior in random solid solutions and annealed systems, where an interesting interplay is observed between misfit components and chemical short-range order affecting the overall critical resolved shear stress. The role of short-range order on the critical yield stress is quantified and compared with current solid solution models. Finally, we propose and validate an extension to the Labusch-Varvenne class of high-concentration solid-solution analytic models that incorporates the effects of chemical short range order. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.