Abstract
The phase-transformation temperatures of a nickel-titanium-based shape-memory alloy (SMA) were initially evaluated under stress-free conditions by the differential scanning calorimetric (DSC) technique. Results show that the phase-transformation temperature is significantly higher for the transition from detwinned martensite to austenite than for that from twinned martensite (or R phase) to austenite. To further examine transformation temperatures as a function of initial state, a tensile-test apparatus with in-situ electrical resistance (ER) measurements was used to evaluate the transformation properties of SMAs at a variety of stress levels and initial compositions. The results show that stress has a significant influence on the transformation of detwinned martensite, but a small influence on the R-phase and twinned martensite transformations. The ER changes linearly with strain during the transformations from both kinds of martensite to austenite. The linearity between the ER and strain during the transformation from detwinned martensite to austenite is not affected by the stress, facilitating application to control algorithms. A revised phase diagram is drawn to express these results.
Original language | English (US) |
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Pages (from-to) | 579-587 |
Number of pages | 9 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 37 |
Issue number | 3 |
DOIs | |
State | Published - Mar 2006 |
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys