Investigation of mechanical properties in welding of shape memory alloys

Shape-memory alloys (SMA) are increasingly used due to the exceptional properties such as shape memory effect (SME), Pseudo elasticity and super-elastic effect (SE). However, mechanical properties of SMA are scantly studied in the field of welding technology. In this study, effect of laser welding on SMA is considered through investigation of mechanical properties as well as microstructure of the weldments. The specimens have been manufactured from NiTi, one of the most popular SMA alloys in the industry, in order to evaluate tensile strength and microstructure before and after the laser welding process. Based on the results, higher ultimate tensile strength and elongation are achieved in the specimens for which the tensile test was carried out in same direction as manufacturing rolling direction. Furthermore, microstructure investigations show that the behavior of solidification is changed from planar to volumetric and/or to dendritic. Due to this evolution, the joint tensile strength and strain reached to 118 MPa and 8%, respectively.