Thermomechanical behavior of Ti-rich NiTi shape memory alloys

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2008-05, Vol.481, p.146-150
• Main Authors: Paula, A.S., Mahesh, K.K., dos Santos, C.M.L., Braz Fernandes, F.M., da Costa Viana, C.S.
• Format: Article
• Language: English
• Subjects: Ausforming; Marforming; Shape memory alloys; Thermomechanical behavior; Ti-rich NiTi
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2007.02.142

Phase transformations associated with shape memory effect in nickel–titanium (NiTi) alloys can be one-stage, B19′ (martensite) ↔ B2 (austenite), two-stage including an intermediate R-phase stage, or multiple-stage depending on the thermal and/or mechanical history of the alloy. In the present paper, we highlight the effect of (i) deformation by cold-rolling (from 10% to 40% thickness reduction) and (ii) final annealing on the transformation characteristics of a Ti-rich NiTi shape memory alloy. For this purpose, one set of samples initially heat treated at 773 K followed by cold-rolling (10–40% thickness reduction), has been further heat treated at various temperatures between 673 and 1073 K. Another sample was subjected to heat treatment at 1040 K for 300 s followed by hot rolling (50%) after cooling in air to 773 K and water quenching to room temperature ( T room). Phase transformations were studied using differential scanning calorimetry, electrical resistivity measurements and in situ X-ray diffraction. A specific pattern of transformation sequences is found as a result of combination of the competing effects due to mechanical-working and annealing.