Evolution of phase transformations after multiple steps of marforming in Ti-rich Ni-Ti SMA
CSN – GGDP/GPD, Rod. BR 393, km 5001, Lúcio Meira, s/n, Vila Santa Cecília, 27260-390 Volta Redonda, RJ, Brazil
2 CENIMAT – I3N, Campus da FCT/UNL, 2829-516 Monte de Caparica, Portugal
Corresponding author: email@example.com
The phase transformations associated with Shape Memory Effect (SME) can be one step, B19' (martensite) ↔ B2 (austenite), or two/multiple steps which include the intermediate R phase, depending on the thermal and thermomechanical history of the alloy. The transformation temperatures are generally observed above room temperature in Ti-rich Ni-Ti alloys, while those observed in Ni-rich alloys occur below room temperature. The goal of the present work is to investigate the phase transformations evolution in Ti-Rich Ni-Ti SMA (Ni-51 at % Ti) when subjected to two distinct thermal treatments (500°C for 30 minutes in air and 800°C for 300 minutes in vacuum) and subsequently multiple steps of marforming thermomechanical treatments intercalated with thermal treatments (500°C for 30 minutes in air) and subsequent four distinct final thermal treatments (400, 450, 500 or 600°C for 30 minutes in air). Further, the stability of phase transformations in the initial ten thermal cycles of these thermomechanically treated samples is also studied. Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) were used to identify the transformation temperatures and the phases that are present after the thermomechanical treatments.
© EDP Sciences, Springer-Verlag, 2008