Suggesting the high-pressure route to metastable high entropy alloys with ultra-large lattice distortions

Abstract

One of the key features of high entropy alloys is their severe local lattice distortions, which can lead to beneficial and unusual combinations of mechanical properties. Most reported high entropy alloys (HEAs) are made of size- and chemically similar elements, but if including a component with a distinct size difference was possible, further increase in distortions could be foreseen. However, such additions have typically been disregarded as such alloys are thought to be unmixable. Here, we predict the possibility of mixing such large elements into well-studied HEAs with the help of high or moderate pressure. Miscibility of three large elements in two alloy systems has been studied: Mg/Zr addition in CoCrFeMnNi alloy and Pb addition in MoNbTaTiV alloy. These new compositions are metastable at ambient conditions but can be stabilized with high pressures and probably quenched to ambient with suitable temperature–pressure protocols. We predict that some of the promising candidates can be thermodynamically stabilized at 15–20 GPa, or even lower pressures at elevated temperatures. If synthesized and quenched to ambient conditions, these metastable HEAs would possess ultra-large lattice distortions.