Mechanical properties and deformation mechanisms of precipitation-strengthened heterogeneously structured FeNi-based medium-entropy alloy

Abstract

Conventional high-performance superalloys typically rely on substantial amounts of costly Ni and Co, raising material costs and restricting widespread industrial use. We adopt a Fe-rich FeNi-based multi-principal element alloy with the nominal composition Fe40Ni30Co10Cr10Al5Ti5 (at.%) as a model system. Via heavy cold rolling followed by a two-step thermal treatment (800°C/30 min + 550°C/48 h), we successfully achieve a dual heterogeneous architecture comprising ultrafine/lath-shaped precipitate colonies together with microcrystalline zones containing spherical precipitates. At 273 K, the alloy’s yield strength reaches 1529 MPa, its ultimate tensile strength attains 1697 MPa, and its elongation measures 20%. When tested at 823 K, these values become 1010 MPa, 1230 MPa, and 25%, respectively — mechanical attributes that outperform most analogous alloys. Further mechanistic analysis reveals that during deformation, particularly at elevated temperatures, the outstanding performance arises not only from ordering strengthening owing to nanoscale γ′ phases but also from pronounced back-stress hardening induced by the heterogeneous structure.