Refractory High-Entropy Alloys Produced from Elemental Powders by Severe Plastic Deformation

A comparative investigation of two fundamentally different approaches for the synthesis, microstructure evolution, and mechanical properties of the refractory high-entropy alloys (RHEA) HfNbTaTiZr and HfNbTiZr is performed. The two methods comprises conventional arc (button) melting and a powder route based on mechanical alloying and consolidation via severe plastic deformation. In particular, blended elemental powder is pre-compacted and subjected to one or four passes of equal channel angular pressing (ECAP) at 500 degrees C and then 10 revolutions of high pressure torsion (HPT) at room temperature to an effective strain between 4 and 40. Some samples are then annealed at 500 degrees C for 1 h to investigate the thermal stability of the phases. The four ECAP passes at 500 degrees C do not result in the formation of the body-centered cubic (BCC) phase typical for the program RHEAs despite the presence of interfacial zones between particles and defect-driven diffusion. Nevertheless, a single ECAP pass is sufficient to create a solid bulk sample for subsequent HPT. After 10 HPT revolutions, in contrast to melting route resulting in a single BCC phase alloy, both alloys form new phases comprising a Nb-rich BCC phase and a ZrHf-rich HCP phase in both alloys. First time the refractory-high-entropy alloys (RHAEs) are manufactured through the solid-state joining of elemental powders at low temperatures using severe plastic deformation (SPD). The current approach facilitated the exploration of mechanisms involved in the formation of new phases and enabled variations in composition and thereby the optimization of RHEAs.image (c) 2024 WILEY-VCH GmbH