A high stability B2-containing refractory multi-principal element alloy

An equiatomic HfNbTaRuZr refractory multi-principal alloy was cast via arc melting and characterized in both as-cast and vacuum annealed conditions. (Nb, Ta)-rich body-centered cubic (BCC), (Hf, Ru)-rich B 2, and (Hf, Zr)-rich hexagonal close-packed (HCP) phases in annealed materials were identified by both xray diffraction and transmission electron microscopy, with all phases stable from 1350 to 1575 degrees C. At 1575 degrees C the alloy contained 35.9 % of a morphologically stable B 2 phase. Preferential segregation of oxygen and nitrogen to the HCP phase was observed. The volume fractions of the HCP and B 2 phases increased and decreased, respectively, with increasing annealing temperature. Lamellar microstructures present along grain boundaries were determined to result from a discontinuous transformation from a disordered BCC phase to B 2 and BCC. Refinement of the grain size and microstructure was achieved by splat quenching, resulting in exceptional hardness due to nano-scale precipitates.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.