A new phase inversion mechanism in refractory high-entropy superalloys: Volumetric phase inversion driven by an asymmetric miscibility gap

Abstract

Refractory high-entropy superalloys (RHESAs) often exhibit an inverted microstructure—an ordered B2 matrix with disordered A2 precipitates—which limits their applicability. While topological phase inversion has been reported in RHESAs, we identify a distinct mechanism, termed volumetric phase inversion (VPI), that reverses the matrix and precipitate phases purely through temperature change. This inversion, observed in a model RHESA, is driven by a strongly asymmetric miscibility gap (MG). The asymmetry arises from unequal shifts in their Gibbs free-energy minima with temperature, primarily due to distinct Al partitioning and differing thermodynamic responses. The mechanism is validated using subregular solution modeling in two ternary proxy subsystems, both reproducing asymmetric MG behavior and confirming the enthalpy–entropy interplay. To our knowledge, this is the first report of a temperature-driven reversal of phase volume fractions in a metallic system. These findings establish VPI as a new thermodynamic pathway for microstructural control in RHESAs and beyond.