Refinement strengthening, second phase strengthening and spinodal microstructure-induced strength-ductility trade-off in a high-entropy alloy

The strength-ductility trade-off of high-entropy alloy (HEA) is a major factor affecting its potential application. In this work, the mechanical properties and deformation mechanisms of as-cast and cold rolled-annealed (RA) Fe23Co24Ni24Cr21Al8 (at%) HEA samples were comparatively investigated. Compared with as-cast sample, the cold-rolled and annealed sample possessed higher yield strength (725 +/- 12 MPa), ultimate strength (1042 +/- 23 MPa) and sustained good ductility (46.7 +/- 4.5%), suggesting excellent strength-ductility combination was achieved in RA sample. The as-cast and RA samples both possessed dual phases including FCC and BCC, but the volume fraction of BCC in as-cast sample was very few. The RA sample exhibited significantly decreased grain size and more volume fraction of BCC compared with as-cast sample, indicative of the refinement strengthening and second phase strengthening. Meanwhile, a high density of dislocation walls and spinodal decomposition structure were observed in RA sample, which contributed to the outstanding ductility.