Achieving the strength-ductility balance in heterogeneous (FeCrCoNi)₉₅B₅ high-entropy alloy by laser surface remelting

Excellent strength-ductility combination is always the eternal pursuit for high-entropy alloys (HEAs) to broaden their industrial applications. Herein, a soft laser-affected region is achieved in hard as-rolled (FeCrCoNi)₉₅B₅ plate to form soft-outer and hard-inner heterogeneous architecture by the laser surface remelting (LSR). The unaffected as-rolled matrix consists of face-centered cubic (FCC) lamellar nanostructures (∼51 nm) and plate-like body-centered tetragonal (BCT) particles (∼2 μm). The laser-affected region is divided into transition and remelted layers. FCC phase in the transition layer grows to refined equiaxed grain (∼1.3 μm), while BCT size remains. Slightly refined FCC matrix (∼1 μm) surrounded by lamellar FCC-BCT nano-eutectic boundaries (∼20 nm) are formed in the remelted layer. Microstructure evolution in laser-affected regions can be attributed to non-uniform heat distribution and inherent elemental characteristics of (FeCrCoNi)₉₅B₅ HEA. Compared to homogenized and as-rolled samples, LSR-treated HEAs show excellent strength-ductility balance. Specifically, optimized LSR-treated sample possesses a high tensile yield strength (YS) of ∼1131 MPa, accompanied by a tensile fracture elongation (FE) ∼10.4 %, showing around 4 times higher YS than that of the homogenized sample and 6.5-fold increase in FE than that of the as-rolled sample. The superior strength-ductility balance of the LSR-treated sample is attributed to the hetero-deformation induced (HDI) strengthening caused by soft-outer and hard-inner heterogeneous structures. The soft laser-affected region can accommodate more dislocations during the plastic deformation process to arise better cooperative strengthening with the hard as-rolled matrix. This work provides helpful guidance for optimizing heterogeneous HEAs with superior strength-ductility balance and expanding their practical applications.