Heat Setting and Mechanical Property Analysis of U-shaped Nickel-titanium Alloy Wire

Different heating conditions are applied to shape the nickel-titanium alloy wires, the mechanical properties and internal structure of the nickel-titanium alloy wires are studied, and the optimal heat setting process parameters for the nickel-titanium alloy wires are determined. The tensile properties of Ni-Ti wires are tested by tensile tester. The metallographic structure of the Ni-Ti wire is observed by optical metallographic microscope. The results show that the higher the heat setting temperature and the longer the heating time, the better the heat setting effect of the Ni-Ti wire and the closer the size of Ni-Ti wire to that of the setting die. The stresses of the top and the bottom plateaus of Ni-Ti wire decrease over the heating time, and when the temperature is 550℃ and the heating time is 20 min, the stresses of the top and the bottom plateaus are the smallest. The residual strain increases significantly when the heating time is more than 10 min. With the increase of the temperature and the heating time, the distribution of austenite structure in Ni-Ti wire is more uniform, the austenite grain boundary becomes more obvious, and the average grain size of the structure becomes larger.