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. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).