Precipitation Behavior of the Topologically Close-Packed Phase in the DD5 Superalloy during Long-Term Aging.

The precipitation behaviors of the topologically close-packed (TCP) phases in the bicrystal DD5 superalloy have been investigated. The results showed that the [001] crystallographic orientations are consistent with that of adjacent grains; however, the direction of the needle-like TCP phases is not consistent with that of the γ phase channels. The angle between needle-like TCP phases and γ phase channels is 45°, but the angle between the needle-like TCP phases of the adjacent grains is equal to the misorientation of the adjacent grains. Furthermore, during long-term aging, the needle-like TCP phases gradually decompose and transform into globular and short rod-like phases. The TCP phases precipitate preferentially in the dendrite. It is difficult to precipitate at the interdendrite/grain boundary, which is caused by the segregation of the constituent elements of the TCP phase to the dendrite.