Effect of Nd-YAG laser welding on the functional properties of the Ni-49.6at.%Ti

Laser welding technology is applied successfully for joining several metallic compounds. Using a Nd-YAG source the process is suitable for precision welding of low thickness metallic sheets. In this work a Nd:YAG laser was used for welding 0.54 mm thick tapes of Ni-49.6at.%Ti shape memory alloy (SMA). Two different microstructural states of the material were chosen (fully recrystallized and partial annealed after 30% cold working) to investigate pseudoelastic and shape recovery behaviours. For the two different metallurgical conditions the mechanical properties of both reference and laser welded samples were tested at several temperatures by stress-strain measurements. A systematic comparison of the results was carried out. Moreover, differential scanning calorimeter (DSC) investigations on samples taken from the heat affected zone and hardness measurements allowed further clarification that the modification was induced by the welding procedure. The results obtained on the fully recrystallized material indicate that the stress-induced martensite and the recovery mechanisms are weakly modified by the presence of the welding zone while the pseudoelastic properties of the partial annealed material are strongly affected. (