The mechanisms of preferential occupation and planar defect transformation in the μ phase of cobalt-based superalloys

The μ phase, a type of topologically close-packed phase, is commonly found in superalloys, and the planar defects within it play a crucial role in mechanical properties, creep behavior, and high-temperature durability. However, due to the complexity of the TCP phase, researches on the formation of various planar defects and their interactions, especially at the atomic scale, remain scarce. In this article, advanced aberration-corrected electron microscopy and atomic-resolution elemental analysis methods are employed to investigate two types of planar defects in the μ phase in combination with the theoretical calculations. Given the similarity in atomic arrangement and elemental occupancy between these two planar defects, transformation mechanisms between these two planar defects are proposed. Additionally, observations reveal that different transition metals, such as Cr, exhibit varying preferential distribution tendencies both within the μ phase and near the defect interfaces, which is due to the reduction of the formation energy of the μ phase and its internal defects, thereby enhancing the stability of these structures. Our findings provide theoretical support for understanding the transformation between different planar defects in the μ phase and the distribution behaviors of various elements at these defects, offering valuable insights for the design of alloys containing these complex structural phases. © 2025 Acta Materialia Inc.