Refractory high entropy alloys (RHEAs), consisting of a BCC+B2 microstructure, have been reported to exhibit higher strengths at elevated temperatures, as compared to conventional nickel base super alloys. However, the ductility of these alloys has often been limited due to the continuous B2 matrix in these alloys, such as for example, the Al0.5NbTa0.8Ti1.5V0.2Zr RHEA. The ductility of this alloy was dramatically improved by inverting its microstructure from “BCC precipitates in a B2 matrix”, to “B2 precipitates in a BCC matrix” via isothermal annealing experiments. This microstructural evolution leading to the phase inversion, has been investigated in great detail by coupling transmission electron microscopy (TEM), atom probe tomography (APT), and some high-energy beam synchrotron experiments. With the aim to increase this BCC+B2 phase field to elevated temperatures, the microstructural stability of single phase B2 compositions, derived from these alloys, has also been investigated.