镍钛形状记忆合金管的等通道转角挤压

摘要

As a new attempt, equal channel angular extrusion (ECAE) of nickel−titanium shape memory alloy (NiTi SMA) tube was investigated by means of process experiment, finite element method (FEM) and microscopy. NiTi SMA tube with the steel core in it was inserted into the steel can during ECAE of NiTi SMA tube. Based on rigid-viscoplastic FEM, multiple coupled boundary conditions and multiple constitutive models were used for finite element simulation of ECAE of NiTi SMA tube, where the effective stress field, the effective strain field and the velocity field were obtained. Finite element simulation results are in good accordance with the experimental ones. Finite element simulation results reveal that the velocity field shows the minimum value in the corner of NiTi SMA tube, where severe shear deformation occurs. Microstructural observation results reveal that severe plastic deformation leads to a certain grain orientation as well as occurrence of substructures in the grain interior and dynamic recovery occurs during ECAE of NiTi SMA tube. ECAE of NiTi SMA tube provides a new approach to manufacturing ultrafine-grained NiTi SMA tube.%　　作为一种新的尝试，将工艺实验、有限元法和显微分析技术相结合，研究镍钛形状记忆合金管的等通道转角挤压。在等通道转角挤压过程中，镍钛形状记忆合金管内部装有钢芯，然后将其封装在钢套中。基于刚粘塑性有限元法，镍钛形状记忆合金管等通道转角挤压的有限元模拟采用多种耦合边界条件和多种本构模型。通过有限元模拟，获得了镍钛形状记忆合金管等通道转角挤压的等效应力场、等效应变场和速度场。有限元模拟结果和实验结果具有很好的一致性。有限元模拟结果表明，在镍钛形状记忆合金管的转角处，速度场具有最小值，发生大剪切变形。显微组织观察结果表明，在镍钛形状记忆合金管的等通道转角挤压期间，大塑性变形导致晶粒具有一定的取向性，在晶内产生亚结构，并有动态回复发生。等通道转角挤压为制备超细晶镍钛形状记忆合金管提供了一种新的途径。