Strengthening of high entropy alloys by dilute solute additions: CoCrFeNiAlx and CoCrFeNiMnAlx alloys

A theory to predict the initial flow stress of an arbitrary N-component fcc random alloy is extended to predict the additional strengthening when a dilute concentration of a substitutional element is introduced. Assuming properties for the N-component alloy to be established, the theory requires only information on the elastic and lattice constants of the new N + 1-alloy, and makes a parameter-free prediction for the strength increment due to the added N + 1st element. The theory is applied to the CoCrFeNiAlx and CoCrFeNiMnAlx systems, achieving good agreement with experiments. The theory thus serves as a valuable tool for guiding design of new fcc random alloys. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Predicting yield strengths of noble metal high entropy alloys

Recent data on the Noble metal (Pd-Pt-Rh-Ir-Au-Ag-Cu-Ni) high entropy alloys (HEAs) shows some of these materials to have impressive mechanical properties. Here, a mechanistic theory for the temperature-, composition-, and strain-rate-dependence of the initial yield strength of fcc HEA5 is applied to this alloy class, with inputs obtained through "rule-of-mixtures" models for both alloy lattice and elastic constants. Predictions for PdPtRhIrCuNi are in good agreement with available experiment and the model provides useful insights into this system. The model is then used to explore other alloy compositions within this broad class to guide design of new stronger Noble metal HEA5. (C) 2017 Acta Materialia Inc. Published by. Elsevier Ltd. All rights reserved

Average-atom interatomic potential for random alloys

An average-atom (A-atom) embedded-atom-method potential for random multicomponent alloys at any composition is derived analytically and validated by comparing A-atom and true random alloys bulk and defect properties, in model Fe-Ni-Cr systems. The A-atom can be mixed with the individual alloying-element potentials, thus enabling computation of defect/defect interactions. Its use provides quantitative insight into the physical role of the fluctuations, and has many applications, such as in atomistic/continuum modeling of random alloys and the development of new potentials with controlled properties

Solute-strengthening in elastically anisotropic fcc alloys

Dislocation motion through a random alloy is impeded by its interactions with the compositional fluctuations intrinsic to the alloy, leading to strengthening. A recent theory predicts the strengthening as a function of the solute-dislocation interaction energies and composition. First-principles calculations of solute/dislocation interaction energies are computationally expensive, motivating simplified models. An elasticity model for the interaction reduces to the pressure field of the dislocation multiplied by the solute misfit volume. Here, the elasticity model is formulated and evaluated for cubic anisotropy in fcc metals, and compared to a previous isotropic model. The prediction using the isotropic model with Voigt-averaged elastic constants is shown to represent the full anisotropic results within a few percent, and so is the recommended approach for studying anisotropic alloys. Application of the elasticity model using accessible experimentally-measured properties and/or first-principles-computed properties is then discussed so as to guide use of the model for estimating strengths of existing and newly proposed alloys