Effect of Ta interlayer on laser welding of NiTi to AISI 316L stainless steel

To improve the quality of the weldment between nickel titanium (NiTi) and AISI 316L stainless steel wires, laser welding with tantalum interlayer was attempted by means of a fiber laser system. The presence of Ta interlayer and its thickness were found to have a significant effect on the chemical composition, microstructure and mechanical properties of laser-welded NiTi-316SS joints. By increasing the Ta content in the weld joint, the content of brittle intermetallic compounds (TiFe4, TiCr2, TiFe, etc.) was reduced. The tensile stress and strain of the welded joints at fracture reached 251 MPa and 2.7% by adding a 50-μm Ta interlayer, as compared to the weldment of NiTi to AISI 316L stainless steel (134 MPa and 0.63%) without Ta interlayer. With excessive (>50 μm) Ta addition in the weld joint, the mechanical properties deteriorated due to the excessive formation of new intermetallic phases TaCr2 and Ni3Ta, and the fracture region was at the weld-316L SS interface, where cracks were formed during tensile testing.