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

A comparative investigation of two fundamentally different approaches for thesynthesis, microstructure evolution, and mechanical properties of the refractoryhigh-entropy alloys (RHEA) HfNbTaTiZr and HfNbTiZr is performed. The twomethods comprises conventional arc (button) melting and a powder route basedon mechanical alloying and consolidation via severe plastic deformation. Inparticular, blended elemental powder is pre-compacted and subjected to one orfour passes of equal channel angular pressing (ECAP) at 500 °C and then 10revolutions of high pressure torsion (HPT) at room temperature to an effectivestrain between 4 and 40. Some samples are then annealed at 500 °C for 1 h toinvestigate the thermal stability of the phases. The four ECAP passes at 500 °C donot result in the formation of the body-centered cubic (BCC) phase typical for theprogram RHEAs despite the presence of interfacial zones between particles anddefect-driven diffusion. Nevertheless, a single ECAP pass is sufficient to create asolid bulk sample for subsequent HPT. After 10 HPT revolutions, in contrast tomelting route resulting in a single BCC phase alloy, both alloys form new phasescomprising a Nb-rich BCC phase and a ZrHf-rich HCP phase in both alloys.