Dissimilar laser welding of NiTi wires

NiTi shape memory alloys are well-known due to their outstanding functional properties including superelasticity (SE) and Shape Memory Effect (SME). Laser welding is a viable technique for the joining of NiTi wires, which are employed in the design of smart structures. Joining of dissimilar wires can provide better flexibility using various alloys and, consequently, lead to multi-functional properties. However, this is really challenging due to the effect of temperature on microstructure and composition of the welded joints, since the thermal process alters the material microstructure and subsequently the transformation temperature of the heat affected area. Therefore, it is of utmost relevance to find the optimal laser operational parameters for this process. In this context, this study investigates the dissimilar laser welding of NiTi wires. The experimental investigation is based on several interconnected analyses that include optical microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) analysis. Thermal analysis by Differential scanning calorimetry (DSC) is also performed to check the matching between the thermal transition of the welded joints compared to the reference materials. Highest energy delivered during welding led to welded joints of better quality. Lastly, the identification of the optimal operational parameters of the laser welding process, such as laser power and scan speed, was found to be crucial to preserve microstructural properties of the welded wires, thermal transition temperatures and therefore avoid to affect the functionality of the materials.