Stronger weld than base metal in face-centered cubic alloy through multi-scale heterogeneity

Welds with face-centered cubic (FCC) structure are inherently weaker and more susceptible to mechanical failure than base metal (BM). Here, we report a breakthrough approach that reverses this fundamental weakness. Compositional inhomogeneity in weld metal (WM) reduces FCC phase stability, preferentially promoting deformation-induced martensitic transformation in WM over BM. Additionally, spatial variation in metastability between the WM and BM activates a gradual progression of martensitic transformation from WM toward BM. Our welds exhibit exceptional cryogenic strength (104%) and ductility (140%) compared to BM, outperforming state-of-the-art alloys. These findings provide promising solutions to the long-standing issue of weld degradation in cryogenic environments.