Study of the mechanisms of slip transfer at grain boundaries in fcc bulk material by the combination of in situ atomic force microscopy and orientation gradient evaluation by HR-EBSD

晶界滑移不仅影响材料的静强度，而且对材料的疲劳行为也有重要影响。然而，晶界对材料强度的影响是矛盾的：虽然晶界可以提高材料的静态强度，但晶界在疲劳情况下可以起到裂纹萌生的作用。为了理解这种静态强度的增加和晶间裂纹的萌生过程，对晶界滑移转移机制的详细了解是必不可少的。了解金属塑性变形过程中的这一关键过程对于理解和优化材料的力学行为是必要的。以往对滑移传递过程的研究仅限于透射电子显微镜薄层实验和分子动力学模拟，基于实验结果，可以建立滑移传递过程的通用模型。这两种方法的结果是否可以转化到物质的行为是一个悬而未决的问题，也是利用我们的新方法填补这个项目的知识空白。虽然我们的初步工作主要致力于晶界抵抗整体滑移转移的问题，但这个项目的目的是为阐明潜在的位错机制提供有价值的贡献。原位原子力显微镜和原位HR-EBSD与软件Crosscourt的直接和新颖的组合使我们能够根据位错运动引起的滑动位错密度的确定和几何上必要的位错的取向梯度来评估靠近晶界的位错过程。位错的吸收和塑性不相容的吸收，就像晶界的松弛过程一样，可以通过晶界取向错位的变化和HR-EBSD的(伪)位错密度测量来实现。在这个项目的范围内，我们将在前期工作的基础上，将已经成功应用的测量方法，如3D-FIB层析成像、3D-EBSD和HR-EBSD以及原子力显微镜与同步原位取向梯度测量相结合，并将其应用于滑移传输过程的研究。我们将采用和扩展常用的标准评估方法，如标准奈张量分析或使用EBSD的错动密度测量，从而使首次有可能在真实的宏观样品中研究晶界的滑移转移过程。

The slip transfer at grain boundaries influences not only the static strength of materials, but it also influences the fatigue behavior of materials significantly. However, the impact of grain boundaries on the strength of materials is ambivalent: While grain boundaries may increase the static strength of materials, grain boundaries can function as crack initiation sites in the case of fatigue. In order to understand this increase in the static strength and the intergranular crack initiation process, a detailed knowledge of the slip transfer mechanisms at the grain boundary is indispensable. The understanding of this key process during plastic deformation of metals is necessary to understand and to be able to optimize the mechanical behavior of materials.Previous studies on the slip transfer process have been limited to TEM thin-layer experiments and MD simulations for which, based on experimental results, common models for the slip transfer process could have been developed. The transferability of the results from both methods to bulk material behavior is an open question and the gap of knowledge to be filled with this project by using our new methods. While our preliminary work was mainly devoted to the issue of grain boundary resistance to bulk slip transfer, the aim of this project is to provide a valuable contribution to the elucidation of the underlying dislocation mechanism.The direct and novel combination of in situ atomic force microscopy and in-situ HR-EBSD with the software CrossCourt allows us to evaluate dislocation processes close to grain boundaries based on the determination of the dislocation density from sliding caused by the dislocation motion and from the orientation gradients due to geometrically necessary dislocations. The absorption of dislocations and of plastic incompatibilities as far as the relaxation processes in the grain boundary become accessible from a change in the misorientation of the grain boundary and by a (pseudo) disclination density measurement by HR-EBSD. Therefore, we gather a complete insight in the slip transfer process in a bulk material.Within the scope of this project, based on our preliminary work, we will combine measurement methods already successfully applied such as 3D-FIB tomography, 3D-EBSD and HR-EBSD as well as atomic force microscopy with simultaneous in situ orientation gradient measurement and apply it to the problem of the slip transfer process. We will adapt and expand common standard evaluation methods such as a standard Nye-tensor analysis or a disclination density measurement using EBSD and thus making it possible for the first time to investigate the slip transfer process at grain boundaries to a closed understanding in real macro samples.