INFLUENCE OF THERMAL TREATMENTS AT THE TEMPERATURES OF TRANSFORMATION AND MICROSTRUCTURE OF A NiTi ALLOY
memory form alloy, nitinol, transformation temperatures, heat treatment.
In the present work the influence of heat treatments on the microstructural transformations of an approximately equiatomic NiTi- memory form alloy was investigated. A NiTi wire with 2.5 mm in diameter, work hardened as received, was submitted to annealing heat treatments at 450°C and 500°C in order to verify the calorimetric and microstructural changes. Optical and electronic microscopy and X-rays diffraction were employed to characterize the structure and the phases morphology. The analysis via differential scanning calorimetry allowed the determination of the transition temperatures (Ai, Af, Mi, Mf), which showed relevant variation associated to the annealing temperatures. The microstructure in the work hardened condition and after the annealing heat treatments was analysed in detail via field emission scanning electronic microscopy (MEV-FEG).