U型镍钛合金丝热定型及力学性能分析

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

采用不同的加热条件对镍钛合金丝进行定型,研究镍钛合金丝的力学性能及内部组织结构,确定了镍钛合金丝的最优热定型工艺参数。使用拉伸所用强力仪对镍钛丝进行拉伸性能测试,使用光学金相显微镜对镍钛丝进行金相组织观察。结果表明,热定型温度越高,加热时间越长,镍钛丝热定型效果越好,镍钛丝尺寸越接近定型模具尺寸;镍钛丝上下平台应力随加热时间的增加变小,其中,加工条件为550℃、20 min的上下平台应力最小,残余应变在加热时间多于10 min时显著增加;随着温度和加热时间的增加,镍钛丝内部奥氏体组织分布越来越均匀,奥氏体晶界越来越明显,其组织晶粒平均尺寸也越来越大。

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.