Laser-welding of a Ni-rich TiNi shape memory alloy: Mechanical behavior

A Nd:YAG laser was used for joining a pseudoelastic Ti-51.5 at.% Ni shape memory alloy. Tensile tests on sheet metal of 0.5 mm thickness were performed at temperatures of -40 degrees C, +20 degrees C and 110 degrees C, representing the martensitic, pseudoelastic and austenitic condition, respectively. Laser-welded specimens exhibited an ultimate tensile strength of about 820 MPa not affected by the test temperature. This value corresponds to 80% of the ultimate tensile strength of the base material which was also tested in its martensitic, pseudoelastic and austenitic condition. Therefore, the full use of stress-induced martensite formation on welded components is ensured. However, for a comprehensive understanding of microstructural changes resulting from laser-welding investigations of the 0.6 mm weld were carried out by optical and transmission electron microscopy. Their results will be presented and discussed with respect to the tensile tests. Observation of fracture surfaces of ruptured specimens by scanning electron microscopy confirmed the ductile behavior of laser-welded joints.