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 B2, and (Hf, Zr)-rich hexagonal close-packed (HCP) phases in annealed materials were identified by both x-ray diffraction and transmission electron microscopy, with all phases stable from 1350 to 1575 °C. At 1575 °C the alloy contained 35.9 % of a morphologically stable B2 phase. Preferential segregation of oxygen and nitrogen to the HCP phase was observed. The volume fractions of the HCP and B2 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 B2 and BCC. Refinement of the grain size and microstructure was achieved by splat quenching, resulting in exceptional hardness due to nano-scale precipitates.