Laser shape setting of superelastic NiTi wire: effects of laser beam power and axial pre-load

Abstract

Shape setting is one of the most important steps of the production route of shape memory alloys, because the programmed shape and functional properties, such as the shape memory effect and the superelasticity, can be fixed. The conventional NiTi shape setting is performed throughout a low temperature (400 °C–500 °C) furnace treatment of constrained material. Recently, it was demonstrated the feasibility of an advanced method, based on using a laser beam scanning, to induce the functional performances on thin NiTinol wires. We studied the effects of the principal process parameters, like laser power and axial pre-load, on functional properties, microstructure and cycling of straight laser annealed Nitinol thin wires. The collected results were then compared to the performances obtained with the commercial wires. It was demonstrated that optimal superelastic behavior can be achieved by optimizing the laser power, while the variation of the applied stress did not affect the wire performances. Laser treated wires shown reduced mechanical hysteresis compared the commercial reference one.