Development of a Localized Heat Treatment Tool for Shape Memory Alloy Wires using an Ytterbium Fiber Laser.

Abstract

Creating localized areas of shape memory effect or superelastic effect in a shape memory alloy wire is quite a complicated task. To produce these localized effects in feasible applications it is necessary to precisely control the temperature profile of the treated wire. This is due to a shape memory alloy's notorious sensitivity to composition and heat treatment. In this thesis, a localized heat treatment system based on a one-dimensional heat transfer model coupled with the precise control of a high powered fiber laser has been developed. Also, a variable flow inert gas heat treatment chamber that is specially designed to eliminate the oxide formation in shape memory alloy heat treatments without causing significant forced convection cooling has been developed. Several experiments have been performed in which various heat treatments are prescribed by the model, and then validated by real-time thermocouple temperature measurements. It is demonstrated that localized changes in superelasticity occur, where the treated region takes on shape memory effect properties and even shows signs of precipitate hardening when overaged. More studies are needed to determine specific heat treatment processes that induce desired SMA properties, but this is beyond the scope of this thesis.