Precipitation characteristics of a nickel-based single-crystal superalloy after long-term thermal exposure

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Abstract
Microstructural stability is of great importance for the application of rhenium-containing nickel-based single-crystal superalloys. The microstructures of single-crystal superalloy DD6, especially the precipitation characteristics before and after thermal exposure, were characterized using scanning electron microscopy, transmission electron microscopy, and related techniques. Acicular M 6C carbides, rod-like M 6C carbides, and granular μ phases have been observed in the aged alloys, and the orientation relationships of these precipitates have been identified. During the early stage of M 6C precipitation, the carbide maintains a cube-on-cube orientation relationship with the matrix, whereas further growth of the M 6C carbides leads to a twin-related orientation relationship. For the granular μ phases containing a high concentration of Re, no special relationship has been observed. The results of the study will be beneficial for the understanding and improvement of nickel-based single-crystal superalloys.

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