Effect of interlayer addition on microstructure and mechanical properties of NiTi/stainless steel joint by electron beam welding

NiTi/Stainless Steel (SS) sheets have been welded via a vacuum electron beam welding process, with three methods (offsetting electron beam to SS side without interlayer, adding Ni interlayer and adding FeNi interlayer), to promote mechanical properties of the NiTi/SS joints. The joints with different interlayers are all fractured in the weld zone near the NiTi side, which is attributed to the enrichment of intermetallic compounds including Fe2Ti and Ni3Ti. The fracture mechanisms of different joints are strongly dependent on the types of interlayers, and the joints without interlayer, adding Ni interlayer and adding FeNi interlayer exhibit cleavage fracture, intergranular fracture and mixed fracture composed of cleavage and tearing ridge, respectively. Compared with the brittle laves phase Fe2Ti, Ni3Ti phase can exhibit certain plasticity, block the crack propagation and change the direction of crack propagation. The composite structure of Ni3Ti and Fe2Ti will be formed when the FeNi alloy is taken as the interlayer, which provides the joint excellent mechanical properties, with rupture strength of 343 MPa. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

NiTi/Stainless Steel sheets have been welded via a vacuum electron beam welding process with three methods to improve mechanical properties of the joints. The joints fractured in the weld zone due to the enrichment of intermetallic compounds. Different joints exhibit different fracture mechanisms depending on the types of interlayers, and using FeNi alloy as the interlayer can form a composite structure of Ni3Ti and Fe2Ti, providing excellent mechanical properties.