Heterogeneous nucleation and microstructure formation in peritectic alloy systems

在最初的提案中为整个资助期设定的全球目标仍然是系统的研究，旨在了解包括所有阶段的合金包晶凝固过程中的异质形核和微观结构形成。这项工作将有系统地继续进行，同时还将受到最不发达国家方案内其他小组成果的启发。第二个资助期的具体目标可概括为：(I)生成和利用高精度的热力学和成分数据，以建立精确和一致的热力学描述；(Ii)进一步发展相场模型和生成模拟微观组织；(Iii)定向凝固样品的微观组织分析；(Iv)高级量热和相场研究的更紧密耦合，以更深入地了解包晶凝固四个阶段中的每一个阶段的作用；阐明四个阶段对包晶反应类型和外部凝固参数(温度梯度G和凝固速率v)的影响。Al-Ni系是研究III型和II型包晶的一个很好的模型系统，因此Al-Ni系的研究工作将得到进一步的推进。Al-Cu系被选为研究II型和II型包晶的额外和独立的材料体系。此外，选择这两种合金系统将通过与SP的同事交换重要数据来加强现有的网络。在这项工作中，我们认识到包晶凝固的性质使得无法直接测量大多数反应的动力学性质。我们相信，通过仔细研究包晶凝固从最终组织到生长及其三个不同阶段的尺度阶梯，并通过实验和模拟相结合，可以弥合到异质形核的差距。通过减少相场模拟中参数选择的自由度，可以缩小形核参数的不确定范围。此外，相场模型与实验结果的更紧密耦合使联合分析广泛的实验技术成为可能。否则无法比较的结果可以输入到能够描述所有凝固条件的统一相场模型中。这就是我们在亚琛和克劳斯塔尔的团队在这个联合项目中合作的优势和优点。

The global goal - set in the initial proposal for the entire funding period - remains the systematic research aiming at the understanding of heterogeneous nucleation and microstructure formation during peritectic solidification of alloys comprising all stages. This work will be systematically continued, while also being inspired by the results of other groups within the SPP. Furthermore, the focus of the project will shift in the next two years, bridging the scale difference between microstructure evolution and nucleation.The specific goals for the second funding period can be summarized as: (i) the generation and utilization of high precision thermodynamic and constitutional data to build refined and consistent thermodynamic descriptions; (ii) further development of the phase-field model and generation of simulated microstructures; (iii) microstructure analysis of directionally solidified samples; (iv) closer coupling of advanced calorimetric and phase-field investigations for a deeper understanding of the role of each of the four stages of peritectic solidification; and (v) clarify the interplay between the four stages on the type of peritectic reaction and the external solidification parameters (temperature gradient G and solidification rate v). Work on the Al-Ni system will be advanced since this is an excellent model system for investigating peritectics of type III and type II. As additional and independent material system Al-Cu has been chosen to investigate type II and type I peritectics. The choice of both alloy systems will, moreover, strengthen the existing network by exchange of important data with colleagues in the SPP.For this work we recognize that the nature of peritectic solidification makes it impossible to directly measure most kinetic properties of the reaction. We believe that by meticulously investigating peritectic solidification down the scale ladder from final microstructure over growth and its three different stages, and by coupling experimentation with simulation, the gap to heterogeneous nucleation can be bridged. By reducing the degrees of freedom for the choice of parameters in the phase-field simulation, the uncertainty range for the parameters of nucleation can be closed. Also, closer coupling of the phase-field model with experimental results makes it possible to jointly analyze a broad range of experimental techniques. Results, which would otherwise not be comparable, can be fed into a unifying phase-field model that is capable of describing all solidification conditions. This is the strength and beauty of this cooperation between our groups in Aachen and Clausthal in this joint project.