Mechanisms of phase strengthening and thermal stabilization in the refractory high-entropy superalloy AlMo0.5NbTa0.5TiZr

Refractory high-entropy superalloys (RHESs) offer transformative potential for high-temperature applications, but face significant challenges in engineering applications. This study investigates the strengthening mechanisms for different phases and phase stability of the AlMo_0.5NbTa_0.5TiZr RHESs, which features a γ/γ′-like A2/B2 dual-phase nanostructure. Based on Energy-dispersive X-ray spectroscopy (EDS) analysis, the composition of the BCC phase in this RHESs was identified and corresponding alloys were successfully synthesized. Uniaxial compression tests reveal temperature-dependent synergy between BCC and B2 phases: while both phases exhibit near-equal strength contributions at elevated temperatures (600–800 °C), mechanistic analysis revealed distinct origin that the BCC phase derives strength from solid-solution effects dominated by lattice distortions, whereas the B2 phase provides order-strengthening through antiphase boundary energy barrier. Meanwhile, it has been fully demonstrated that incorporating high-modulus and large atomic-size elements (e.g., Mo, Zr, Cr) effectively enhances solid-solution strengthening in single-phase RHEAs. In-situ transmission electron microscopy (TEM) heating experiments uncover rapid coarsening of BCC precipitates driven by spinodal decomposition. The microstructural instability to elemental redistribution was found to be linked to Nb/Ta-Zr miscibility gaps. These findings provide critical guidelines for designing RHEAs suitable for high-temperature engineering applications.