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

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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.