Residual stress analysis in laser welded NiTi sheets using synchrotron X-ray diffraction

Synchrotron radiation was used for fine probing the different regions of a laser welded NiTi joint.Measurementswere taken at 0.2mmintervals, starting in the non-thermal affected material, through the heat affected zone, thefusion zone and again across the heat affected zone finishing in the basematerial. Along the longitudinal directionthe residual stresses were found to be always tensile in the heat affected and fusion zones; along the transversaldirection, an inversion of the stress stateswas found. Themagnitude of the residual stresseswas found to bemoresignificant in the transversal direction due to constraints imposed during welding. The heat introduced duringwelding has a stress relief effect on the cold-rolled base material, although it does not promote any solid-statetransformation. The effect of the heat input on the residual stress pattern and magnitude was identified and itwas seen that high heat input leads to a higher magnitude of the residual stresses in the weld and the stress reliefeffect is observed over a larger extension from the weld centerline. This paper presents the first experimentalstudy on the determination of residual stresses on laser welded NiTi shape memory alloys