• Santos, Christian Mariani Lucas Dos
• Santos, Paula Andersan Dos
• Viana, Carlos Sérgio C. Da Costa
• Fernandes, Francisco Manuel Braz
• Mahesh, Karimbi Koosappa

Abstract

<p>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.</p>

Topics

• impedance spectroscopy
• nickel
• resistivity
• phase
• x-ray diffraction
• differential scanning calorimetry
• titanium
• annealing
• quenching
• hot rolling