Method for determining diffusion data in ternary and multicomponent alloys

在拟议的项目中，将详细介绍一种新的方法，允许通过合理的实验努力来确定多组分合金中的原子迁移率，包括它们与温度的关系。该方法由定向凝固实验、温度梯度扩散实验、扩散计算和优化算法组成。将以Al-Mg-Zn系的fcc-Al相作为模型材料来开发和验证新的方法，并将创建在扩展的样品长度上呈现系统变化的浓度梯度的样本。为此，对稳态凝固过程中的凝固速度进行了多次突变，重新调整了稳态凝固速度。这会造成凝固浓度的波动，从而封闭相对较窄的浓度区间。样品将在温度梯度中进行退火，以诱导具有局部变化动力学的扩散过程。在对每个单扩散实验进行评价时，可以忽略原子迁移率的浓度依赖关系，并且可以假定扩散过程仅与温度有关。从扩散实验中，原子在扩展的温度区间内的迁移率将是可以获得的。对于三元合金的扩散方程将用扩散参数的近似来求解，并将实现对这些参数的优化程序。从初始浓度分布出发，根据随温度变化的迁移率函数，计算了扩散热处理过程中浓度分布的演化。将要阐述的优化算法通过最小化从扩散实验获得的浓度分布与扩散计算得到的浓度分布之间的总偏差来适应迁移率函数。在多组分扩散过程中出现的化学势梯度的相互作用效应导致了扩散剖面的特殊特征，例如在其他合金元素的浓度梯度附近增加了浓度梯度。这些功能将提供有关个人移动功能的详细信息。新方法将极大地减少目前建立或扩展移动数据库的巨大工作量。

In the proposed project a novel method will be elaborated that allows determining atomic mobilities in multicomponent alloys including their temperature dependence with reasonable experimental effort. The new method will consist of a variation of a directional solidification experiment, a diffusion experiment in a temperature gradient, a diffusion calculation and an optimization algorithm. The fcc-Al phase of the Al-Mg-Zn system will be used as the model material to develop and verify the new method.Samples that exhibit systematically varying concentration gradients over an extended sample length will be created. For this, the solidification velocity during steady state solidification is abruptly changed several times and the steady state is re-adjusted. This creates fluctuations in the solidifying concentration which enclose relatively narrow concentration intervals.The samples will be annealed in a temperature gradient to induce diffusion processes with locally changing kinetics. During the evaluation of each single diffusion experiment, the concentration dependence of the atomic mobilities can be neglected and diffusion processes can be assumed to be solely temperature dependent. From the diffusion experiments, atomic mobilities in an expanded temperature interval will be accessible. The diffusion equation will be solved for ternary alloys with approximations for the diffusion parameters, and an optimization routine for these parameters will be implemented. Starting with the initial concentration profiles, the evolution of the concentration profiles during the diffusion heat treatment is calculated on the basis of the temperature dependent mobility functions. The optimization algorithm that is to be elaborated adapts the mobility functions by minimizing the total deviation between the concentration profiles obtained from the diffusion experiment and the diffusion calculation. Interaction effects of the chemical potential gradients that occur during multicomponent diffusion cause special features in the diffusion profiles such as increasing concentration gradients in the vicinity of concentration gradients of the other alloying elements. These features will provide detailed information on the individual mobility functions.The currently immense effort for building up or extending mobility databases will be drastically reduced by the new method.