Zr-4合金动载下绝热剪切带的演化及其微观形成机制

In this project, different strain levels of Zr-4 alloy subjected to dynamic loading were obtained by means of the controlled strain rate. After dynamic compression, the classification of the adiabatic shear bands including the deformed bands and transformed bands were distinguished according to the characterization of adiabatic shear bands. Meanwhile, the relationship between the deformed bands, transformed bands and the principal strain was investigated, and the evolution of adiabatic shear bands in Zr-4 alloy subjected to the dynamic loading was revealed. The deformed microstructures in the transformed bands were characterized by the double techniques of the electron backscatter diffraction (EBSD) and transmission electron microscope (TEM), and the point to origin cumulative misorientation in the deformed grains was analyzed during the formation of the transformed bands. Furthermore, the temperature rising caused by plastic deformation in the transformed bands was calculated according to the constitutive equation, and the dynamics of the formed high angle boundary assisted by sub-grains rotation was explained. Finally, the formation mechanism of the microstructure in the transformed bands was revealed, and the physical model of the formation of the ultrafine and equiaxed in the transformed bands was constructed.

本项目拟通过控制应变速率实现Zr-4合金动态加载下不同的应变水平。基于动态加载后绝热剪切带的表征，鉴别绝热剪切带的类型：形变带和转变带，研究主应变与形变带和转变带之间的关系，揭示Zr-4合金动态加载下绝热剪切带的演化过程。利用电子背散射衍射和透射电镜相结合的技术，细致表征转变带内部的微观组织，分析转变带形成过程中晶内累计取向差的变化，并结合本构方程计算转变带内部塑性变形造成的温升以及亚晶旋转形成大角晶界的动力学过程，揭示转变带内部组织的形成机制，建立转变带内部细小等轴晶粒形成的物理模型。

项目通过试验设计和应变冻结的试验方法实现了Zr-4合金高应变速率下应变的单一分离，在不同应变下发现了两种类型的绝热剪切带：形变带和转变带，获得了形变带和转变带形成所需的临界主应变：形变带形成所需的临界主应变为0.21，而转变带形成所需的临界主应变为0.30。采用FIB定点切割减薄技术成功制备出转变带内部组织的分析样品，精细表征了转变带内部组织的微观结构，转变带内部组织主要大晶粒（200～500 nm）和细小晶粒（约10 nm）相互嵌套的结构混合而成，在原子尺度上转变带内部组织无明显偏析的现象。基于热模拟压缩试验构建了Zr-4合金的本构方程，计算了局部塑性变形所做的温升，并基于位错理论计算了转变带内部组织的旋转动力学过程，在热力学和动力学上支撑转变带内部组织形成过程的预测，构建出转变带内部组织形成的物理模型。