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 0.5 NbTa 0.5 TiZr 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.