Annealing of cold-worked equiatomic Ti-Ni alloy followed by DSC and TEP methods

Abstract

Systematic studies have been carried out in an equiatomic Ti-Ni shape memory alloy deformed 40% at room temperature (martensitic state) by cold working. The deformed alloy was submitted to four different annealing temperatures (385°C, 425°C, 465°C and 505°C ) for accumulated times. The evolution of martensitic transformation was evaluated by DSC (Differential Scanning Calorimetry). The corresponding TEP (Thermoelectric Power) was measured in the martensitic state around room temperature. Both, the temperature and the time of annealing, are important parameters which affect the martensitic transformation. On the DSC curves, after short annealing times two peaks appear during cooling, which correspond to the R phase and the martensitic phase transformations. The temperature of the martensitic transformation increases with annealing time. On the other hand, the R phase transformation temperature is practically unchanged for all annealing times. The TEP measured in the martensitic state exhibits a clear evolution during the annealing. It has been shown that there is some relationship between TEP measurements and temperature of the martensitic transformation DSC peak, during the annealing treatments after 40% cold- work.