Simulations on the interaction between grain boundaries and precipitates

该项目的目标是开发一个非常详细的理解和分析模型，用于晶界和第二化学相沉淀物之间的相互作用，即钉扎力或“Zenger阻力”。这种力在材料生产中至关重要，因为它控制着微观结构的演变，从而控制着涉及再结晶和晶粒生长的加工步骤中的材料性能。尽管如此，尽管钉扎力的重要性，目前的物理理解是相当不完整的，可以看出，从事实上，现有的模型只涉及非常少的细节，具体的沉淀物和晶界。例如，目前的模型不涉及任何关于沉淀物和晶界之间的界面或晶界接触沉淀物的三线的信息。同样地，目前的模型没有考虑到弯曲晶界将比平坦晶界同时接触并与更多沉淀物相互作用的事实。这种倾向被认为是Friedel位错钉扎模型成功的主要因素。与目前使用的非常详细的位错钉扎（强化）模型相比，晶界钉扎的影响仅以初步的方式得到了解决。这意味着，尽管它们的重要性，目前的齐纳阻力模型可能是相当不准确的。拟议项目的目标是开发全面的新模型的齐纳阻力，考虑了许多潜在的重要影响。一个多尺度的方法，其中原子的细节相结合，一个更大的规模的模型，以获得均匀的结果。首先，在原子论的基础上研究了晶界与析出相相互作用的细节。使用分子动力学，从各种具体类型的沉淀物的各种晶界的分离进行了模拟。同样的脱钉过程也模拟使用顶点模型，在该模型中，晶界和沉淀物界面表示的抽象，刻面平面。这些模型的直接比较，例如通过将顶点模型调整为原子模型，允许理解关于去钉扎过程的所有细节，使得可以识别、量化和判断最重要的影响的重要性。其次，顶点模型可以用于模拟晶界与真实的沉淀物阵列的相互作用。因此，高度精确的模型齐纳阻力的推导，无论是再结晶和晶粒生长。这些可以在以后用于改善制造工艺和材料性能。

The goal of the project is to develop a very detailed understanding and analytical model for the interaction between grain boundaries and precipitates of secondary chemical phases, i.e. the pinning force or "Zenger drag". This force is of utmost importance in the production of materials because it controls the microstructure evolution and hence the material properties during processing steps involving recrystallization and grain growth. Still, in spite of the importance, the current physical understanding of the pinning force is rather incomplete, as can be seen from the fact that the existing models involve only very little detail about the specific precipitates and grain boundaries. For instance, current models involve no information at all about the interface between the precipitate and the grain boundary, or the triple line where the grain boundary touches the precipitate. Likewise, the current models do not account for the fact that a curved grain boundary will touch and interact with more precipitates concurrently than a flat one. This tendency is known to be the principal element in the success of the Friedel model for dislocation pinning. In comparison to the highly detailed dislocation pinning (strengthening) models in use today, the effect of grain boundary pinning has only been addressed in rudimentary ways. This means that in spite of their importance, the current Zener drag models are probably rather inaccurate. The proposed project is aiming to develop comprehensive new models for the Zener drag that consider a multitude of potentially important influences. A multi-scale approach is used in which atomistic detail is combined with a larger scale model to derive homogenized results. Firstly, the details of a grain boundary interacting with one precipitate is investigated on an atomistic basis. Using molecular dynamics, the detachment of various grain boundaries from various concrete types of precipitates is simulated. The very same depinning processes is also simulated using a vertex model, in which the grain boundary and the precipitate interface are represented by abstract, facetted planes. The direct comparison of these models, e.g. by adjusting the vertex model to the atomistic one, allows to understand all detail about the depinning process, so that the most important influences can be identified, quantified and judged in respect of importance. Secondly, the vertex model can then be utilized to simulate the interaction of a grain boundary with realistic arrays of precipitates. Hence, highly accurate models for the Zener drag are derived, both for recrystallization and grain growth. These can later be used to improve manufacturing processes and materials properties.