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High Entropy Alloys (HEAs) designate a class of multicomponent metallic alloys in nearly equiatomic compositions. According to the constituting postulate, a larger number of constituents in a solid solution increases its configurational entropy, which has a maximal value when constituents exist in equiatomic concentrations and this is sufficient to overcome enthalpic contributions between the alloy components which would otherwise favor compound formation or phase separation. This entropy effect would, thus, stabilize disordered, crystallographically simple, solid solutions. Since then, numerous HEA candidate systems have been experimentally studied. It is unclear, however, if, and to which extent, the configurational entropy can be accessed by the system in the way it is suggested. The present work deals with this question using theoretical/computational methods. First, a series of model Body Centered Cubic (BCC) systems involving strong symmetric interactions between unlike atom pairs (referred to as “equinteracting” systems), containing up to five components, is investigated using the Cluster Variation Method in the irregular tetrahedron approximation. The symmetry of interactions, though artificial, allows for the straightforward presentation of phase diagram sections even for quaternary and quinary systems. Next, a “real” HEA candidate system, VNbTaMoW, which presents the BCC structure, is investigated by ab initio calculations, allowing to extend the conclusions to a realistic case with asymmetric interactions. The results show that configurational entropy has a small, even marginal, effect on phase transitions and the competition between conflicting interactions in the solid solution ( i.e. frustration ) seems to be the relevant factor behind the observed stabilization in the disordered states in HEA systems. [ABSTRACT FROM AUTHOR]

The supercell approach to first-principles calculations of an alloy's full phonon spectrum is computationally expensive. It is therefore rarely used for calculating temperature dependent free energies of alloy phases or for calculating alloy phase diagrams. Amid the wider acceptance of uncertainty evaluation and the use of more efficient methods for materials design, the supercell approach is revisited and a simpler and more computationally efficient approximation is proposed. The new method is then used to calculate the Cr-Ni temperature dependent thermodynamic properties and phase diagram, resulting in predictions that are in good agreement with previous thermodynamic assessment. The new approach can facilitate accurate and rapid CALPHAD thermodynamic assessments of multi-component systems. [ABSTRACT FROM AUTHOR]

U-Nb's discontinuous precipitation, γ matrix bcc → α cellular orth + γ cellular ′ bcc , is intriguing in the sense that it allows formation and growth of the metastable γ ′ phase during the course of its occurrence. Previous attempts to explain the thermodynamic origin of U-Nb's discontinuous precipitation hypothesized that the energy of α forms an intermediate common tangent with the first potential of the double-well energy of γ at the γ ′ composition. In this work, we examine different possible mechanisms by which the discontinuous precipitation product in the U-Nb system can be stabilized. We put forward a mechanism by which the bulk free energy of the γ can develop a non-monotonic dependency with composition. Additionally we posit that local contributions due to lattice mismatch between the α and γ phases may be responsible for the generation of metastable states that may stabilized by thermodyna mics as well as by kinetics. Our work suggests that local misfit strain tends to play a crucial role in the growth of the discontinuous precipitation product. Depending on the magnitude of strain developed at the α / γ ′ interfaces, either an increasing γ ′ composition or a random distribution of γ ′ compositions around the equiatomic value with respect to increasing temperature could be expected. Moreover, we show how it is possible to stabilize the discontinuous precipitation front through highly anisotropic and fast interface diffusion. [ABSTRACT FROM AUTHOR]

Insufficient availability of molten salt corrosion‐resistant alloys severely limits the fruition of a variety of promising molten salt technologies that could otherwise have significant societal impacts. To accelerate alloy development for molten salt applications and develop fundamental understanding of corrosion in these environments, here an integrated approach is presented using a set of high‐throughput (HTP) alloy synthesis, corrosion testing, and modeling coupled with automated characterization and machine learning. By using this approach, a broad range of CrFeMnNi alloys are evaluated for their corrosion resistances in molten salt simultaneously demonstrating that corrosion‐resistant alloy development can be accelerated by 2 to 3 orders of magnitude. Based on the obtained results, a sacrificial protection mechanism is unveiled in the corrosion of CrFeMnNi alloys in molten salts which can be applied to protect the less unstable elements in the alloy from being depleted, and provided new insights on the design of high‐temperature molten salt corrosion‐resistant alloys. [ABSTRACT FROM AUTHOR]