Metastable high entropy alloys of TiZrHfTa with glass-like characteristics at low temperatures

Metastability engineering of high entropy alloys can widen the alloy-design window through the access of a potentially huge configuration space. At the same time, it has the great capacity to overcome the strength-ductility trade-off, where often one witnesses an actual performance improvement at low to cryogenic temperatures. An in-depth microscopic understanding of the underlying mechanism is now needed to drive the design effort. Here we investigate in detail the energetic, structural and chemical complexity of Ti–Zr–Hf–Ta system. The large configuration space with local chemical interaction heterogeneity is explored by a combination of structure-searching techniques and accurate energy models constructed by cluster expansion based on density functional theory data. We find that the potential energy landscape evolves towards displaying shallow mega-basins when decreasing the Ta content. This is accompanied by an expansion of the configurational density of states, which evolves to be clearly distinct from that of a homogeneous random solid-state solution. Furthermore, the energy-state variability and local configuration flexibility are identified from high throughput analysis of atomic structures and their energies. Such features remind closely what found in glass-like systems. This work suggests a theoretical connection between glass physics and metastability engineering of HEAs is quite promising.