Microstructural evolution and mechanical properties of autogenous electron beam and laser beam welded joints in Ti6Al4V/Nitinol dissimilar alloys

Abstract

Dissimilar joints between titanium (Ti) and nickel (Ni) alloys are increasingly sought after in different advance applications. Specifically, the combination of Ti6Al4V and Nitinol offers potential benefits in aerospace, energy sectors and biomedical devices where titanium's strength and Nitinol's shape memory properties can be leveraged. This study explores the feasibility of joining dissimilar Ti6Al4V and Nitinol alloys via Electron Beam Welding (EBW) and Laser Beam Welding (LBW) without an interlayer. Both the welding techniques produced stable joints. A comparative analysis reveals that EBW and LBW exhibit distinct microstructural evolution and mechanical properties. EBW samples showed a higher Ultimate Tensile Strength (UTS) of 160 ± 5 MPa, corresponding to a joint efficiency of ∼27% with respect to the Nitinol (weaker material) base alloy strength, compared to 120 ± 5 MPa for LBW samples, which exhibited a joint efficiency of ∼20%. Energy Dispersive X-Ray Spectroscopy (EDS) and X-Ray Diffraction (XRD) analysis detected Ti₂Ni and NiTi intermetallic compounds (IMCs), with a relatively higher concentration of Ti₂Ni in LBW samples. Ti₂Ni layer was formed at the titanium alloy interface during EBW, but at the nickel alloy interface during LBW. Tensile tests indicated that the fracture happened at areas of high concentration of Ti₂Ni in EBW and LBW joints. This comprehensive study highlights the potential of EBW and LBW for dissimilar titanium-nickel alloy joints without an interlayer and offers insights that can be used in future research via optimized welding parameters and interlayer when necessary.