Strength–Ductility Balance in Additively Manufactured Laminated Fe-Cr-Ni/Fe-Cr-Ni-Cu Alloy Heterostructures

Fe-Cr-Ni-Cu alloy has been extensively utilized over the past few decades due to its low cost yet high strength. Nevertheless, the poor ductility of this alloy limits its real application in industrial fields. In this study, a soft Fe-Cr-Ni alloy was combined with a Fe-Cr-Ni-Cu alloy by laser-directed energy deposition (LDED) to fabricate the laminated Fe-Cr-Ni/Fe-Cr-Ni-Cu heterostructure, which achieved a high strain hardening capacity and superior strength–ductility balance. Results illustrate that the homogeneous Fe-Cr-Ni-Cu alloy exhibits the largest ultimate tensile strength (UTS) of 990.5 ± 20.41 MPa and contrarily, the lowest fracture elongation (FE) of 11.65% ± 1.97%. In comparison, the heterostructure which underwent LDED with UTS of 913.01 ± 6.99 MPa and FE of 36.4% ± 1.59% demonstrates a more than threefold increase in ductility with a slight sacrifice in strength compared to the homogeneous Fe-Cr-Ni-Cu alloy. The exceptional mechanical property of the heterostructure can be attributed to the hetero-deformation-induced (HDI) strengthening and strain hardening, precipitation strengthening, and transformation-induced plasticity (TRIP) effect. HDI strengthening, strain hardening, and TRIP effect collectively contribute to the enhancement of both strength and ductility, while precipitation strengthening also improves the strength. This work proposes a new strategy for the preparation of high-strength alloys with excellent ductility throughout the design of the laminated heterostructure with alternating soft and hard phases via an LDED technology, providing insights for the development of advanced materials with superior mechanical properties.