Tuning cryogenic strength-ductility synergy and phase stability in an additively manufactured 316L through in-situ alloying

The influence of nickel (Ni) on the mechanical properties and deformation performance of 316L austenitic stainless steel is multifaceted, significantly impacting its overall suitability for engineering applications. Three kinds of 316L-based alloys with different Ni contents were fabricated via in-situ alloying during laser powder bed fusion. The results indicate that Ni addition had a negligible effect on the original microstructure. Compared with the 316L sample (yield strength 688 MPa, elongation 40%), the alloy with 1 wt.% Ni addition exhibited a simultaneous increase in strength and ductility at 87 K, reaching a yield stress of 801 MPa, an ultimate tensile stress of 1467 MPa, and a total elongation of 42.2%. Increasing the Ni addition to 2.5 wt.% further enhanced the yield strength to 958 MPa; however, the ultimate tensile strength (1334 MPa) and elongation (32%) decreased due to the suppressed martensitic transformation. Higher Ni content increased the stacking fault energy (SFE) thus stabilised the austenite and suppressed the martensitic transformation. Consequently, a balanced martensitic transformation accounted for the excellent strength-ductility synergy in 316L+1Ni sample. This finding provides an insight in manufacturing metastable materials with superior strength-ductility synergy in cryogenic environment by manipulating the SFE through in-situ alloying during additive manufacturing.