High strength and high ductility in a novel Fe40.2Ni11.3Mn30Al7.5Cr11 multiphase high entropy alloy

Abstract

In the present study, a novel Fe40.2Ni11.3Mn30Al7.5Cr11 high entropy alloy displaying an excellent combination of high strength and high ductility has been developed. The b.c.c.+B2/f.c.c. dendritic-interdendritic microstructure was characterized using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy, and the alloy’s mechanical properties were examined using Vickers hardness measurements and room-temperature tensile tests. The phase stability of Fe40.2Ni11.3Mn30Al7.5Cr11 was investigated by annealing the alloy between 1173 K–1273 K, and the presence of both Ni-rich, b.c.c. needle-shaped precipitates and Cr-rich, σ phase particles was observed for the 1173 K annealed specimen. The σ phase precipitates contributed to the rapid age-hardening effect in the material annealed at 1173 K. A further increase in ageing temperature to 1223 K and 1273 K led to the dissolution of the σ phase and a reduction in the volume fraction of the b.c.c./B2 dendrites, which led to a consequent drop in room-temperature yield strength from the as-cast value of ∼593 MPa–∼486 MPa and ∼228 MPa for the specimens annealed at 1223 K and 1273 K, respectively. An accompanying increase in ductility was observed from ∼22% for the as-cast alloy to ∼27% and ∼40% after annealing the material at 1223 K and 1273 K, respectively. Post-deformation transmission electron micrographs revealed that the f.c.c interdendrites accommodated plastic strain via wavy slip and moreover, deformed before the b.c.c. dendritic regions, which were reinforced by B2 particles and acted as obstacles to moving dislocations. The discovery of a multi-phase HEA that contains 11% Cr and good mechanical properties has relevant high-temperature structural applications especially in cases that require suitable corrosion resistance.