Microstructure and properties of laser micro welded joint of
TiNi shape memory alloy
TiNi shape memory alloy
(1. National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology,
Nanchang Hangkong University, Nanchang 330063, China;
2. State Key Laboratory of Advanced Welding and Joining,
Harbin Institute of Technology, Harbin 150001, China)
Nanchang Hangkong University, Nanchang 330063, China;
2. State Key Laboratory of Advanced Welding and Joining,
Harbin Institute of Technology, Harbin 150001, China)
Abstract: Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet (SMA) was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.
Key words: TiNi shape memory alloy; laser micro welding; microstructure; properties; phase transformation behavior