Microstructure and hydrogen sorption of severely deformed TaTiVCrFe and ZrTiVCrFe refractory high-entropy alloys.

Abstract

Multi-phase refractory high-entropy alloys with hydride forming elements containing body-centered cubic and Laves phases have a great potential in solid-state hydrogen storage applications. Significant hydrogen sorption capacity close to ambient temperature without activating together fast hydrogen sorption kinetics are considered as important delima for this purpose. The present investigation was conducted to process TaTiVCrFe and ZrTiVCrFe refractory high-entropy alloys by severe plastic deformation in order to satisfy these requirements. Two alloys represented noted multi-phase microstructure before and after high-pressure torsion process. In addition, thermal stability of severely deformed samples were studied after long-term annealing at an elevated temperature of 973 K. Fast hydrogen sorption was detected up to 1.04 and 2.53 wt% for severely deformed TaTiVCrFe and ZrTiVCrFe alloys, respectively, with no incubation time. Introducing structural defects, formation of a high-volume fraction of interfaces between different phases due to phase fragmentation and formation of nano/micro cracks in the severely deformed microstructure provided faster diffusion pathway and more nucleation of hydrides. High thermal stability of the processed alloys allow them to use the advantages of severe plastic deformation on the functional properties of refractory high-entropy alloys over a wide temperature range.