Influence of heat treatment on the fatigue life of a laser-welded NiTi alloy wire

The influence of heat treatment on the rotating–bending fatigue of a laser-welded superelastic NiTi alloy wire was investigated. In comparison with the as-welded and annealed at 500 °C for 1 h specimens, the specimen annealed at 400 °C for 1 h shows the best fatigue resistance. The difference of fatigue life in the heat-treated materials is attributed to the different Ti3Ni4 precipitate size. Heat treatment to produce smaller coherent precipitates (10 nm) improves the fatigue resistance of the laser-welded NiTi alloy wire. When the Ti3Ni4 precipitates become coarse, the fatigue resistance decreases.