The Effect of Heat Treatment on SMA's Mechanical and Temperature Transition Region Properties

In the processing of nitinol, there are four main parameters that control the superelastic and shape memory properties:  alloy composition, amount of cold work and time & temperature of thermal processing.  Alloy composition and the degree of cold work have been reported in the past.  To build on our knowledge, this paper aims to give a better understanding of the effect of heat treatment (time and temperature), on the mechanical and Temperature Transition Region (TTR) properties.  Two binary, A_s of -15oC and +95oC, nitinol alloy wires were selected to be tested.  Each wire tested had a diameter of 1mm and a cold work of 45%.  These wires were then heat treated at various times (ranging from 1min to 1hr) and temperatures (ranging from 400oC to 700oC).

A MTS tensile machine and a TA DSC were used to obtain the mechanical and temperature transition region properties.  Metallographic analysis was used to evaluate any microstructure changes that resulted from the heat treatments.