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

• Applicant: Professor Dr. Christian Motz
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2018 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 411096820

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.

• DFG Programme: Research Grants