Investigation of phase transformation kinetics of nitinol alloy aged at different temperatures

Nitinol alloy is an intermetallic compound occurring from binary alloy system between Ni and Ti elements, the elements are equal or between 49 and 51% atomic proportions. The most important feature of this alloy is the display shape memory effect and superelasticity. Alloy realizes these properties thanks to martensitic phase transformations occurring in microstructures due to changing temperature. In addition to these properties, the alloy exhibits corrosion resistance and biocompatibility. The phase transformation properties of the alloy due to the temperature effect are influenced by the Ni content of the constituent components in large amounts. In addition, the intermetallic phases formed in the alloy by heat-treatment or aging can change the components of the main phase and thus change phase transformation properties. Nitinol alloy is used especially in the medical field and in many industrial sectors. Alloy ratios and thermal history must be well defined according to the places of use. For this purpose, Nitinol alloy specimens, consisting of Ni-49.8Ti alloys, were placed in a heat treatment furnace at 1000 ° C for 30 minutes and then discharged into cold water. Subsequently, the samples were allowed to stand in the heat treatment furnace at different temperatures (500 °C, 600 °C, 700 °C), and then cooled to room temperature with different cooling rates (0,2 °C / min, 0,5 °C / min, 1 °C). Thus, after different aging temperatures, the microstructures, phase transformation kinetics and shape memory properties of the Nitinol alloy were tried to be investigated.