Stability in Phase Transformation After Multiple Steps of Marforming in Ti-Rich Ni-Ti Shape Memory Alloy

Nickel-titanium (Ni-Ti) alloys are the most attractive among shape memory alloys (SMA) due to their good functionality properties coupled with high strength and ductility. The transformation temperatures in Ti-rich Ni-Ti SMA can be altered by subjecting them to suitable thermal and/or mechanical treatments to obtain martensitic transformation in one or more steps above 0 A degrees C. The goal of the present work is to investigate the stability of phase transformation characteristics, such as, type of sequence (one, two, and multiple steps) and transformation temperatures in Ti-Rich Ni-Ti SMA (Ni-51 at.%Ti), after being subjected to an initial heat treatment at 500 A degrees C for 30 min in air followed by multiple steps of marforming (cold rolling, 30% thickness reduction) intercalated with heat treatments at 500 A degrees C for 30 min in air and a final heat treatment at four different temperatures (400, 450, 500, and 600 A degrees C) for 30 min in air atmosphere. Differential scanning calorimetry (DSC) and electrical resistivity (ER) were used to identify the phase transformation sequences and the stability of transformation temperatures during initial 10 thermal cycles for each sample with distinct thermo-mechanical treatment.