Study on Mechanical Properties of Annealed NiTi Shape Memory Alloy Based on DIC

The effects of rolling direction and annealing temperature on the mechanical properties of Ni-55.7Ti shape memory alloy sheets were studied by uniaxial tensile test. In the experiment, the two-dimensional digital image correlation method (DIC) was used to measure the deformation information in the process of loading and unloading. The results show that among the unannealed specimens, the tensile strength of the NiTi alloy specimen along the rolling direction is highest and the ultimate strain is smallest. The recovery strain ratio of the NiTi alloy specimen with 45° to the rolling direction is 86.68%, and the superelastic property is best, but the energy dissipation capacity per unit volume cycle is insufficient. Among the annealed specimens, the annealed specimens at 500 ℃ and 700 ℃ have excellent ultimate deformability and high tensile strength. The specimens annealed at 400 ℃ and 500 ℃ lose superelasticity. The specimens annealed at 600-800 ℃ have good nonlinear elastic recovery, the residual strain is less than 1.0%, and the superelasticity is good. The σ_Ms of the specimens annealed at 800 ℃ is largest, the recoverable strain ratio can reach 98.58%, and the superelasticity is best.