基于X射线微束衍射技术的HCP结构多晶材料应力/应变自协机制研究

The main objective of this project is intended to explore a critical scientific issue on the relationship between the discontinuous stress/strain distributions, which induced by deformation twinning on both real space and orientation space, and the microscopic mechanism on the stress/strain accommodation. Hexagonal closed packed (HCP) polycrystalline materials including commercial purity Titanium and Zirconium alloys will be used as targeted materials in our investigations. Some breakthroughs will be expected as follows: 1) the evolution of microstructure units (micro-scale stress/strain distribution and grain rotation) during plastic deformation will be investigated by using advanced Differential-aperture X-ray microscopy (DAMX) technique, in combination with high-energy X-ray diffraction. 2) Based on the above-mentioned direct experimental measurements by in-situ synchrotron-based X-ray diffraction, finite element simulation will be performed on modeling the micro-mechanical behavior of deformation twinning in HCP polycrystals for elucidating the anisotropy in plastic flow. 3) The relationship between microstructure units and the strain accommodation of deformation twinning will be established. The mesoscopic and microscopic mechanisms of strain accommodation caused by the interactions of dislocation slip and twinning will further be clarified. The successful execution of this program will promote the in-depth understanding of plastic deformation in HCP polycrystalline materials, which will provide a significant experimental and theoretical basis for further optimization of mechanical properties.

本项目拟围绕"形变孪生所导致的真实空间与取向空间不连续应力/应变分布状态与应力/应变自协机制的关联性"这一关键科学问题，以Ti、Zr等密排六方金属多晶材料为研究对象，利用先进的同步辐射基X射线微束衍射技术并结合高能X射线衍射技术，揭示HCP多晶材料随宏观塑性应变量变化而在三维实空间与取向空间的微观结构单元（位错/孪晶交互作用引起的从晶间跨越到晶内微米尺度的应力/应变分布与晶粒旋转）演化规律，特别是单个晶粒形变孪晶启动前后基体与孪晶及周围晶粒的应力跳跃；并以此原位实验数据为基础，构建包含位错与孪晶形变模式的能够描述HCP多晶体宏观/微观力学行为（包括微应力分布与局域晶体旋转）的先进各向异性有限元模型；重点阐明形变孪生引起的微米级应力不连续变化与形变孪生引起的较低对称结构金属应力/应变自协机制的关联性。研究成果丰富金属材料塑性变形的基础理论，使我国的金属微观力学实验与模拟研究居世界先进水平。

本项目主要是利用同步辐射微束衍射和高能X射线衍射技术，通过表征真实空间与取向空间的不连续应力/应变分布状态，研究了Ti、Zr等六方结构金属形变过程中孪晶/相变等局域变形行为，揭示了局域应力/应变自协微观机制。应用基于衍射的多尺度组织与应力原位表征方法，系统研究了α-Ti形变孪晶及附近基体晶粒的应变分布，发现孪晶片层内部存在大应力梯度，并通过分子动力学模拟证明了该应力梯度的形成与初生孪晶扩展中的缺陷组态（基面层错）密切相关；采用同步辐射高能X射线衍射技术原位研究了充氢前后锆合金的形变/相变行为，阐明了ζ-Zr2H氢化物的结构、惯习关系及相变机制，并应用三维微束衍射技术首次原位表征了氢化物在α-Zr基体晶粒中引起的不均匀应力场及其加载演化；利用分子动力学方法研究α-Zr晶界对辐照损伤的影响，利用嵌入原子方法研究了结构材料纳米粒子的力学行为。上述成果已在SCI期刊论文发表19篇，包括《Acta Materiaia》5篇、《PNAS》1篇、《Materials Science and Engineering A》4篇、《中国材料进展》特邀综述论文1篇等。项目承担人应邀参加18th International Conference on Textures of Materials (ICOTOM-18)大会，代表中国作大会特邀报告。