Effect of phase reversion and recrystallisation on the microstructure and mechanical properties of a metastable medium-entropy alloy

This study systematically investigates phase reversion, recrystallisation kinetics, and micro-texture evolution in 80% cold-rolled metastable Fe 45 Co 35 Cr 10 V 10 medium-entropy alloy (MEA) during isochronal annealing between 625 °C and 900 °C for 300 s. The results elucidate the interplay between phase transformation, discontinuous recrystallisation, and annealing twin formation. A Cr- and V-rich sigma (σ) phase precipitates within the 625–725 °C range, exerting a strong pinning effect on grain boundaries and retarding recrystallisation. The cold-rolled body-centered cubic (bcc) microstructure progressively undergoes phase reversion to face-centered cubic (fcc) grains, with the transformation mechanism strongly dependent on annealing temperature. Below 725 °C, diffusion-based phase reversion dominates, while above 725 °C, the transformation is governed by a martensitic mechanism. Micro-texture modelling based on the Nishiyama–Wasserman orientation relationship and variant selection reveal the origin of each reverted fcc orientation within the deformed bcc texture. A grain average misorientation (GAM) threshold of 0.5° effectively distinguishes reverted and recrystallised fcc grains. From 675 °C, discontinuous recrystallisation within the reverted fcc phase progressively eliminates deformation-induced heterogeneities, culminating in a fully recrystallised, polygonised fcc microstructure with annealing twins by 800 °C. Notably, partial recrystallisation at 725 °C yields the most favourable mechanical response, achieving YS ∼1330 MPa, UTS ∼1346 MPa, and TE ∼42.6%, driven by multi-stage strain-hardening arising from ultrafine recrystallised fcc grains, deformation twinning, and deformation induced martensitic transformation. These findings underscore the importance of tailoring recrystallisation kinetics, secondary phase stability, and fcc grain structure to optimise the strength–ductility synergy in metastable MEAs.