Electromagnetic field-assisted laser welding of NiTi to stainless steel: Towards a lightweight, high-strength joint with preserved properties

In recent years, laser welding has attracted significant attention as a promising technology for joining smart alloys (e.g., NiTi) to structural materials (e.g., SS) thanks to its unique advantages such as exceptional control heat input and narrow fusion zone. However, obtaining a high strength weldment that also preserves the functional properties of the materials being joined together remains a key challenge in this field mainly due to the formation of brittle intermetallic components (IMCs) near and at the interfacial zone. This study investigates a novel technique for laser welding processing of NiTi/SS assisted by an external magnetic field. This technique, referred to as magnetic field supported, is hypothesized to suppress the formation of brittle intermetallics (e.g., TiFe and TiFe2) during the laser welding of NiTi/SS, which, in turn, may improve the performance of the resultant joint. To test the hypothesis, comprehensive experimental assessment of the evolution of structural, mechanical and thermomechanical properties of NiTi/SS joints has been conducted. The findings demonstrate the full suppression of Ti-Fe-based IMCs in the joint area, accompanied by significant improvement in the strength (by 28 %) and ductility (by 137 %) of the MFSed joint when compared with conventional laser welding. Interestingly, negligible changes (∼0.6 °C) in the martensitic transformation temperatures have been obtained.