Insight into the interfacial architecture of a hybrid additively- manufactured stainless steel/Ni-based superalloy bimetal

The joint strength of hybrid additively-manufactured dissimilar metals dominantly depends on the interfacial architecture, whereas its multi-scale microstructure and contributions to mechanical property need further clarity. In this study, we have obtained crack-free and lamella-like interfacial architecture in the transition region of a stainless steel/Ni-based superalloy bimetal conjugated by laser directed energy deposition. Upon rapid solidification, insufficient solute mixing and complex fluid flow endow the interfacial architecture with pronounced concentration fluctuations and interwoven grain/sub-grain structures. Additionally, high-level thermal stresses and misfit strains induce plentiful inter-lamellar crystal defects, including randomly distributed dislocations, misfit dislocation arrays, stacking faults and stacking fault tetrahedral. The alternate soft and stiff lamella architecture decorated by grown-in crystal defects as well as the 3D grain/sub-grain structure interlock is effective in retarding dislocation motion and accommodating further plastic deformation, potentially enhancing the damage tolerance against applied loads.