The so-called high-entropy alloys (HEAs) are a novel class of alloys developed in the early 2000s which do not contain a single major constituent metallic element. Although the early hypothesis that high configurational entropy might act to stabilise a single phase in such systems has generally been rejected, research has stimulated activity that has revealed a rich seam of novel highly alloyed crystalline metallic systems that possess outstanding mechanical performance. Our focus has been on two classes of HEAs: Cantor Alloy based systems, and Refractory alloys.
Work by the Cantor group in Oxford in the early 2000's looked at 16 - 20 element systems but found they were typically multiphase and brittle. However, they identified the five element FeCrMnNiCo system as being predominantly a single fcc phase which solidifies dentrically. Since then the Cantor alloy has recieved a large amount of interest and been shown to have an attractive combination of strength, ductility and toughness, along with interesting nano-twinning deformation mechanism. Current interests in Oxford focus on alloy compositions adapted from the equiatomic Cantor alloy, and effects of advanced processing methods on microstructures and properties.
The second class of alloys we work on are refractory metal based HEAs. These are of interest for nuclear applications particularly if composition provides for low activation under high energy neutron irradiation. We have shown that some of these refractory alloys exhibit remarkably little hardening due to irradiation. We are continuing development of these alloys and their heat treatment schedules using small arc melted billets.
