Elemental segregation behavior and cryogenic strength-ductility synergy in additively manufactured FeCrNiMn multi-principal element alloy

This study investigates the cryogenic strength-ductility synergy of Co-free FCC multi-principal element alloy fabricated by laser powder bed fusion (LPBF), with emphasis on the effects of scanning speed, elemental segregation, and deformation mechanisms. Equiatomic CrFeNiMn alloys were fabricated at scanning speeds of 800-1200 mm/s and characterized by tensile testing at 298 K and 77 K. All specimens exhibited simultaneous increases in strength and ductility at 77 K. The specimen fabricated at 1200 mm/s showed the representative parameter set, with yield strength, ultimate tensile strength, and total elongation increasing from 609 MPa, 706 MPa, and 20.0% at 298 K to 949 MPa, 1170 MPa, and 26.4% at 77 K, respectively. The enhanced uniform elongation from 11.0% to 23.0% indicates sustained work hardening and delayed necking at cryogenic temperature. The as-fabricated alloy consisted of a single FCC phase with fine/columnar grains, low-angle grain boundary networks, and cellular dislocation structures. Mn-Ni co-segregation at cell walls generated local chemical and stress heterogeneity. At 77 K, reduced stacking-fault energy and increased flow stress promoted dense stacking faults, early deformation twinning, and extensive Lomer-Cottrell locks. These features, together with dislocation-cell strengthening, oxide-particle strengthening, and dynamic Hall-Petch strengthening, synergistically contributed to the superior cryogenic strength-ductility combination.