Effect of low temperature annealing on the properties of nano Ni–Ti alloys

Binary 1:1 Ni–Ti alloy has been the work horse for many industrial and of late biomedical applications amongst all shape memory alloys. Apart from being employed for endovascular applications like stents and filters, they are also used as orthodontic braces and in endodontic tools. Ni–Ti drills and files are used in a few procedures with sterilization between uses. However, the effect of these sterilizing heat-treatments on the properties of the tools is not clearly investigated. In addition to this, satisfactory metallurgical explanations for the wear resistance of these alloys in absent in the literature. Therefore, this paper attempts to define the transformational temperatures for the Ni–Ti as-received and low temperature heat-treated conditions have been investigated using Differential Scanning Calorimetry (DSC). Attempts are made to justify their suitability for endodontic applications by evaluating their mechanical strength parameters using the Tensile and Wear tests. It was found that the samples showed did not show much variations in strength when subjected to tensile tests whereas the same was not observed for DSC tests. Ambient temperature x-ray diffraction studies indicate the presence of Austenitic and Martensitic phases in all the samples. DSC results are strongly affected by presence of internal stresses but stress-induced-martensitic forms in all the samples with equal facility.