Evolution of phase transformations after multiple steps of marforming in Ti-rich Ni-Ti SMA |
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Authors: | A S Paula K K Mahesh F M Braz Fernandes |
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Institution: | (1) 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 |
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Abstract: | 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. |
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Keywords: | |
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