Investigation of the recovery and recrystallization processes of Ni50.9Ti49.1 shape memory wires using in situ electrical resistance measurement

The paper aims at the study of electrical resistance variations of Ni50.9Ti49.1 shape memory wires with different values of cold work at different isothermal cycles for evolution of recovery and recrystallization processes. Differential scanning calorimetry (DSC) analysis was used to determine the recrystallization temperatures of samples in different cold drawn states. Optical microscopy was also used to verify the occurrence of the recrystallization process, which could be detected by in situ electrical resistance measurements. TEM results indicated that during annealing at 450 °C for 45 min, nanocrystalline structure formed in the sample with true strain of 0.6. Result showed that in the sample with a high cold drawn value, the subgrain coarsening occurs during annealing which leads to remarkable decreasing of stored energy in the DSC result. The results also showed that the recrystallization process occurs approximately at 600 °C. Newly recrystallized grains were observed after annealing the samples with true strain of 0.2, 0.4 and 0.6 at 600 °C for 40, 10 and 10 min, respectively.