In order to investigate the deterioration of microstructure in service, the intrinsic microstructural stability and performance of DD6 during long-term aging without an external load are investigated. During aging at 980°C, γ′ rafting in 〈100〉 and 〈010〉 directions show no anisotropy due to small driving forces. γ′ coarsening and rafting lead to a monotonic decrease in hardness between 200 and 1000 h. However, precipitation of topologically close-packed (TCP) phases occurs significantly during aging at 1050°C. The amount of TCP phases increases initially, and then almost saturates, which results in a decrease in hardness. However, owing to the reduction in the growth of the TCP phases and coarsening of γ′, the hardness saturates for an aging time greater than 500 h.
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