Fatigue behavior of laser-welded NiTi wires in small-strain cyclic bending

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…In NiTi, it was reported that increasing surface roughness, as usually found in the FZ, may decrease the fatigue-crack growth resistance [218], justifying the decrease in the fatigue strength of the welded material. Brittle-like features in the fracture surface were reported in [154], while in [155] the welded material fractured in a ductile mode.…”

“…For example, the presence of coarse grain size in the thermal affected areas after welding, can be responsible for the decrease on the fatigue life of polycrystalline materials [216]. Conventional fatigue of laser welded NiTi was studied using rotating-bending specimens [154,155] analysing the effect of the imposed strain amplitude on the number of cycles to failure [154] and the influence of the bending frequency on the fatigue strength [155]. As expected, it was observed a decrease on the fatigue properties of NiTi after laser welding, which was attributed to the segregation of solute and impurities upon solidification of the weld metal and to the existence of coarse grain dendritic structures in this region.…”

A study on the corrosion fatigue behaviour of laser-welded shape memory NiTi wires in a simulated body fluid

“…The laser welding experiments were conducted in Ar shielding environment with the flow rate of 25 L/min. The characteristics for BM and WZ in the NiTi laser joints obtained in previous studies [6,11,18] are summarised in Table 1.…”

“…Interested readers are referred to [11] for design of the test rig and details of the BRF test. The key parameters of the BRF test, such as rotational speed and surface strain were controlled at 100 rpm (or 1.67 Hz) and 0.42 % respectively.…”

“…They also investigated the effect of post-weld heat-treatment on the mechanical fatigue in their subsequent study [10]. Chan et al [11] reported the fatigue fracture mechanisms of NiTi laser joints when subject to small strain in BRF. Panton et al [12,13] investigated the thermomechanical fatigue properties of laser-welded and post-weld heat-treated NiTi wires using a custom design setup.…”