Phase Stability and Microstructural Evolution in a Ductile Refractory High Entropy Alloy Al 10 Nb 15 Ta 5 Ti 30 Zr 40

This paper reports the microstructural evolution and phase stability in a newly developed low-density Al10Nb15Ta5Ti30Zr40 refractory high entropy alloy (RHEA) at different temperatures. This alloy composition was adapted from the composition of the B2 phase in a two-phase B2+BCC mixture at 1000°C in the refractory high entropy superalloy Al0.25NbTaTiZr. After homogenizing at a high-temperature, followed by fast or slow cooling to room temperature, this alloy exhibited a nano-scale mixture of co-continuous BCC and B2 phases, resembling a spinodally decomposed microstructure with concurrent ordering. Interestingly, this novel nano-scale BCC+B2 microstructure exhibits excellent room temperature compressive yield strength (~1075MPa) and ductility (true strain at failure ~ 0.55). Annealing at 600°C and 750°C resulted in the formation of additional ordered omega type AlZr2 phase in this alloy. The experimentally observed phase evolution is in fair agreement with CALPHAD predictions.