In situ mapping of deformation twinning evolution in Mg by nano-3DXRD CT

The proposal aims at investigating deformation twinning (DTw) processes in pure Mg, using nano-3DXRD CT, during in situ tensile testing, at several successive deformation steps and while the materials is under load. Crystal orientations, crystal defects and the full local stress tensor will be mapped in the materials during twin initiation and its progressive propagation. Single crystal and polycrystalline samples will be tested, with a focus on the role of slip in twin initiation and propagation mechanisms, as well and the stresses associated with twin-twin and twin-grain boundaries, and twin slip-planes interactions. After the test campaign at ESRF, post-mortem 3D HR-EBSD and detailed TEM analyses will be done on the deformed materials. These experiments will be a unique chance to close the gap between computer modelling and experiments. They will answer several fundamental and debated questions about the roles of local stresses and crystal defects in DTw mechanisms in hcp metals.

本研究提案旨在借助纳米三维X射线衍射计算机断层扫描（nano-3DXRD CT），针对纯镁中的形变孪晶（deformation twinning, DTw）过程开展研究。试验将在原位拉伸加载过程中，于多个连续变形阶段进行，且全程维持材料处于加载状态。在孪晶形核及其渐进扩展阶段，我们将对材料内的晶体取向、晶体缺陷与完整局部应力张量进行测绘。本次试验将涵盖单晶与多晶试样，重点探究滑移在孪晶形核与扩展机制中的作用，以及孪晶-孪晶界、孪晶-晶界对应的应力，还有孪晶与滑移面的交互作用。在欧洲同步辐射装置（ESRF）完成试验环节后，我们将对变形后的材料开展事后三维高分辨电子背散射衍射（3D HR-EBSD）分析与精细化透射电子显微镜（Transmission Electron Microscopy, TEM）表征。本系列实验将为弥合计算机建模与实验研究之间的差距提供难得契机，同时有望解决密排六方（hexagonal close-packed, hcp）金属中形变孪晶机制相关的多项基础性且尚存争议的问题。