NiTi合金中马氏体相变失稳与局部化的原位多场研究

IN SITU MULTI-FIELDS INVESTIGATION ON INSTABILITY AND TRANSFORMATION LOCALIZATION OF MARTENSITIC PHASE TRANSFORMATION IN NiTi ALLOYS

采用数字图像相关(DIC)方法原位测定了NiTi形状记忆合金薄带在单轴拉伸下变形时的应变场,采用红外热成像法(IR)原位测定其温度场,并定量获得了单轴拉伸加载-卸载条件下马氏体带局部化的全场应变与温度信息.同时研究了相变带的形核、扩展、合并、缩减、分裂及消失等过程中相变带内和带外应变场、温度场、厚度场及折曲角场的变化规律.结果表明,相变应变主要集中在相变带内部,而带外应变量很小,温度场和厚度场变化主要集中在相界面移动的前端,折曲角场变化集中在相变前端且带内分布不均匀.

When NiTi shape memory alloys thin strips under the uniaxial tensile deforma- tion, the stress-induced martensitic transformation tends to exhibit strain localization and insta- bility, and the sample shows reversible transformation bands evolution on macroscopic. The displacement, strain and temperature fields were investigated with in situ optical method, and the full-field strain and temperature information about martensitic localization were quantitatively ob- tained during uniaxial loading-unloading conditions. Strain field is calculated by digital image cor- relation （DIC） method, and the temperature field is captured by infrared thermograph, the thickness field and in-plane rotation angle are also calculated by DIC data. The strain, temperature variation, thickness, in-plane rotation both inside and outside of the transformation bands were studied when it nucleation, expansion, combination, reduction and disappear. The results show that transformation strain of the samples are mainly concentrated inside the transformation bands but small outside, and temperature variation mainly concentrated in thc thickness field in transformation bands is 2% smaller than out of bands transformation fl＇onts, the In plane rotation angle is not only concentrated in the transformation fronts, but also heterogeneous in tile transformation bands. In addition, the maximum in-plane rotation angle during tension is 1.5°. The whole loading unloading progress is full thermal coupling, transformation localization, martensite and austenitic critical nucleation stress are greatly influenced by temperature variation.