1 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China 2 Science and Technology on Advanced High Temperature Structural Materials Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095, China
Abstract: K439B nickel-based superalloy is a new type of cast high-temperature material with a temperature bearing capacity of up to 800 ℃, which has important application prospects in large and complex structural components such as engine casings. As the main grain boundary strengthening phase in this alloy, the evolution of carbides during the long-term aging process is still unclear. This article takes K439B alloy as the object and conducts isothermal aging experiments at 800 ℃ for 6 000—10 000 h to study the evolution and transformation mechanism of carbides during long-term aging process. The results indicate that K439B alloy has excellent structural stability. After long-term aging, most of the MC type carbides in the standard heat treated state were still retained in the grain boundaries and interdendritic structures, and only a portion of the MC type carbides decomposed into M23C6-type carbides and γ' phase, no harmful phases (e.g. σ and η) were formed after long-term aging for 10 000 h. The M23C6-type carbides at grain boundaries exhibited two coarsening behaviors. On the one hand, the M23C6-type carbides gradually coarsened and had a uniform width after long-term aging;on the other hand, the coarsened M23C6-type carbides at certain grain boundaries exhibited irregular shapes and even extended towards the interior of the grains. γ′ phase separate two adjacent M23C6-type carbides, resulting in no complete connection of M23C6-type carbides along the entire grain boundaries.
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2024, Vol. 38 
