Development of a localized heat treatment system for shape memory alloy wires using an ytterbium fiber laser

In order to create localized areas of shape memory effect or superelastic effect in a shape memory alloy (SMA) wire, it is necessary to precisely control the temporal and spatial temperature profiles of the treated wire in order to change its composition at specific locations. In this paper, a localized heat treatment system (LHTS) has been developed based on a one-dimensional heat transfer model coupled with a high power fiber laser. This LHTS is capable of achieving various temporal temperature profiles in a point or a section of an SMA wire prescribed by a user. Furthermore, a variable flow inert gas heat treatment chamber has been designed to prevent oxide formation in shape memory alloy heat treatments without causing significant forced convection cooling. Although the method of how to prescribe a suitable temperature profile for a specific SMA property is beyond the scope of this paper, several experiments were carried out to demonstrate the feasibility of localized heat treatment by the proposed LHTS. It has been shown that a region of a superelastic wire can be treated to demonstrate shape memory effects and even show signs of precipitate hardening when over-aged.