Effect of short-time direct current heating on phase transformation and superelasticity of Ti-50.8at.%Ni alloy

The aim of this study was to investigate the effect of short-time DC heating on the phase transformation and superelasticity of a Ti-50.8at.%Ni alloy, which is extensively used as orthodontics arch wires. The alloy was pre-treated in three different conditions prior to the DC heating, including 15% cold-rolling (as-received), 15% cold-rolling and 673 K ageing (aged) and 15% cold-rolling and 973 K annealing (annealed). DC heating was performed using a Shinwa Bender Soarer-II equipment. DSC, XRD and tensile tests were employed to study the alloy's phase transformation behaviour, phase constituents, and superelasticity, respectively. It was found that the aged samples were sensitive to the short-time DC heating treatment and the dissolution of Ti3Ni4 precipitates into TiNi matrix completed within 15 s. In contrast, the as-received and the annealed samples showed little response to the DC heating. Such findings are of direct relevance to applications of TiNi as orthodontic arch wires, which often involve rapid electrical heating for shape setting. (c) 2008 Elsevier B.V. All rights reserved.