Regulating mechanical properties of laser powder bed fusion manufactured CoCrFeMnNi high-entropy alloy using oversaturated boron doping

The laser powder bed fusion (LPBF) manufactured CoCrFeMnNi high-entropy alloy (HEA) presents potential application at cryogenic temperatures, except for a relatively low yield strength (sigma y). In this work, we proposed an oversaturated boron-doping strategy to overcome this insufficiency. Compared to the boron-free and high boron-doping references, the moderate boron-doping LPBF HEA exhibits high strength at temperatures of 77 and 298 K, while maintains favourable ductility, corresponding to a sigma y of 806 MPa with a total elongation (& varepsilon;) of similar to 20% at 298 K, and a sigma y of 1072 MPa with a & varepsilon; of similar to 12% at 77 K, respectively. The improved mechanical properties are attributed to the microstructures composed of refined grains, reduced cell size, oversaturation of boron and the formation of nano-sized Cr2B precipitates at cell boundaries. The grain boundary strengthening, precipitation strengthening, solid solution strengthening and dislocation strengthening contribute to the high sigma y. The interactions between dislocation slip and deformation twins with boride precipitates account for the enhanced strain hardening and favourable plasticity at 77 K. The results demonstrate an effective strategy to establish balanced mechanical properties of LPBF HEA, and provide an inspiration for future works aiming to develop high-performance structural materials over a wide temperature range.