Seminar Dr. Isaac Toda-Caraballo: An overview on the designing High Entropy Alloys

Dr. Isaac Toda-Caraballo: Department of Materials Science and Metallurgy. University of Cambridge (UK)

Within the last two decades, a new type of material has been increasingly explored. Widely known as High Entropy Alloys (HEAs), they contrast with most of the existing metallic materials in which they do not contain a major element, such as steels, aluminium alloys or magnesium alloys. Their original definition assumes 5 or more different elements, with composition between 5% and 35% of atomic content, displaying a BCC or FCC single solid solution. It has been claimed that the high configurational entropy stabilizes the formation of a single solid solution and avoids the formation of secondary phases. They show interesting combination of properties, such as high hardness and ductility, resistance to corrosion and oxidation and/or irradiation resistance; sometimes in addition to relatively low density. Of special industrial interest is that such properties are achieved as-cast or with little thermomechanical treatment.

There is an enormous compositional space to explore, where there is not experimental information and the existing predictive models on multicomponent systems are scarce. Taking 13 mutually miscible elements, in steps of 5% in composition (that could give large differences in properties), there are ~ 2 million of quinary alloys, ~12 million senary alloys and ~35 million septary alloys to be explored. Higher order systems and further refinements on composition take the number of possibilities towards infinity. Therefore, the classical trial-and-error methodology is not suitable to design HEAs.  Large efforts are being made to adapt classical methods and conceive new methodologies to predict properties.

In this talk, an insight on these alloys, and the current strategies proposed to design new High Entropy Alloys with enhanced properties will be presented. The analysis at the atomic level of the lattice distortion in these alloys produced by the presence of such atomic diversity has been seen useful to investigate their properties. Thermodynamic calculations, atomistic simulations and optimization methods are then combined to propose and cast new alloys.

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