A Study on the Residual Stresses in Tungsten Inert Gas and Laser Welded Nitinol Superelastic Alloy

Fusion-based joining techniques such as TIG and Laser are used for the high-quality Nitinol welds. The joining of Nitinol is challenging due to the formation of intermetallic, which results in the loss of Superelastic and Shape Memory Effect behavior. The optimum heat input is necessary to produce high-quality welds especially in thin sheet joining. Autogenous TIG welding with optimum heat input creates the satisfactory Nitinol weld joints consisting narrower heat-affected zones, and prevents the extensive precipitate formation in weld region. In the paper, autogenous TIG and Laser Beam welding were used for the welding of Nitinol superelastic sheet. The SEM fractography and microhardness were studied to understand the weld zone behavior of Nitinol welds. The Deep Hole Drilling technique was implemented to quantify the residual stresses in TIG and Laser Nitinol welds. The weld longitudinal residual stresses are found to be higher than the transverse residual stresses in both, TIG and Laser welds. In the base material, the compressive residual stresses were present up to near yield strength of material.