Forming and two-way shape memory effect of NiTi alloy induced by laser shock imprinting

Nickel-Titanium shape memory alloy (NiTi SMA) is an intelligent material that is a widely applied and studied. The two-way shape memory effect (TWSME) of the NiTi SMA has garnered particular attraction in the further miniaturisation and integration of micromechanical systems. To realise the micro-forming and TWSME of the NiTi SMAs at a micron scale, this study reports a method that involves laser shock imprinting (LSI) technology to induce the TWSME. The production efficiency of this method was significantly higher than that of the thermo-mechanical treatment; the proposed method integrated the induction and forming processes. In this study, the precise and rapid forming of microstructures was realised; meanwhile, the TWSME was induced successfully at the micron scale. Moreover, the experimental results indicated that this method can improve the mechanical properties of the formed part. The LSI-induced TWSME exhibited good thermal cycling stability during the thermal cycling attenuation test, the maximum phase transition angle of bending workpiece began to remain stable after the fourth thermal cycle, and the stability value was approximately 19.0% of the initial bending angle. Furthermore, the feasibility of the LSI-induced TWSME was proved by theoretical analysis, and its strengthening mechanism, phase transition process, and thermal cycling stability were discussed.