CO2 laser welding of NITI/NI-based alloys

Laser welding technology is applied successfully for joining several metallic compounds. Using a carbon dioxide Continuous Wave (CW) laser, the process is suitable for precision welding of thick metallic sheets. In this work, a CO2 laser source was used for welding Ni49Ti51 shape memory alloy (SMA) with Nickel 201, Monel 400, and Inconel 625. All experimental tests were carried out on 4 mm thick, hot-rolled, and fully annealed sheet. A special protective device was manufactured to avoid oxide formation during the welding process. For each material, welding speed, focus height, shielding gas flow rate, and laser power were optimized to limit the extension of the weld metal and of the Heat Affected Zone (HAZ) and to reduce the intermetallic phases formation. Microstructure characterizations of the HAZ were carried out by optical, Scanning Electron Microscope (SEM), and Energy-Dispersive X-ray Spectrum (EDS) analyses. Stress-strain measurements were also performed to study the mechanical behavior of the welded materials. Moreover, Differential Scanning Calorimetry (DSC) investigations on samples taken from the heat affected zone and hardness measurements allowed to further clarify the modification induced by the welding procedure.