Potential of Co-base Superalloys: Hierarchical Microstructures and Nanomechanical Properties of Co3(Al,W)

由于最近发现了一种类似于镍基高温合金的稳定组织，钴基高温合金有望成为高温应用的新一代材料类别。为了改进和优化这些材料，需要了解如何提高微观结构的稳定性。在Co-Al-W三元高温合金中，添加8at.%的铬改变了合金元素的分配，导致在立方析出物中形成更多的颗粒。据报道，这种层次化结构的形成可以改善力学性能。这项工作的目的是为了更好地了解层状组织的形成和演变及其对力学性能的影响，从而阐明钴基高温合金的设计方法。我们将研究内部含有额外夹杂颗粒的孤立立方体析出物的纳米力学性能，以确定它们的影响。这将使用纳米压头变形单个孤立的立方体形状的沉淀物，包括和不包含颗粒。此外，还将表征三元Co82Al9W9和四元Co74Al9W9Cr8的组织演变。这将通过利用具有纳米级横向分辨率的透射电子显微镜与原子探针断层摄影术相结合来实现，以可视化所含颗粒的原子聚集。这种互补的方法允许澄清热力学驱动力，从而澄清相的稳定性。

Due to the recent discovery of a stable microstructure analogous to that of Ni-bases superalloys, Co-based superalloys holds the potential to be a next generation material class for high temperature applications. To advance and optimize these materials, understanding how to improve the microstructural stability is required. In ternary Co-Al-W superalloys, the addition of 8 at.% Cr alters the partitioning of the alloying elements, resulting in the formation of further particles inside the cube shaped precipitates. It has been reported that mechanical properties can be improved by the formation of such hierarchical structures. The proposed work aims at gaining a better understanding of the formation and evolution of hierarchical microstructures and their impact on the mechanical properties for the purpose of elucidating methods of Co-based superalloy design. The nanomechanical properties of isolated cube shaped precipitates with additional inclusive particles insides will be studied to determine their impact. This will be done using a nanoindenter to deform single, isolated cube shaped precipitates with and without the inclusive particles. Additionally, the microstructural evolution of both ternary Co82Al9W9 and quaternary Co74Al9W9Cr8 will be characterized. This will be achieved by utilizing transmission electron microscopy with a lateral resolution on the nanometer scale in conjunction with atom probe tomography to visualize the atomic clustering of the inclusive particles. This complementary approach allows for the clarification of the thermodynamic driving forces and, consequently, the stability of the phases.