Influence of Short-Term Aging Treatment on Precipitation Behavior of DD6 Single-Crystal Superalloy

In this article, the precipitation behavior of primary γ’ (γ’1st) precipitation and secondary γ’ (γ’2nd) precipitation of DD6 during short-term thermal exposure is revealed by high-resolution transmission electron microscopy and scanning electron microscopy. After various times of elevated temperature aging treatment, the γ’1st precipitates show varying degrees of decomposition; meanwhile, the fine secondary γ’ precipitates are heavily nucleated in the γ channel and show a regular morphological evolution process. In the process of elevated temperature aging treatment, sharp crevices start to appear at the edges of the γ’1st precipitates, and present jagged and extensive decomposition behavior with time, and the γ’1st precipitates exhibit directional decomposition behavior due to the annihilation of “positive” and “negative” edge dislocations at the γ / γ’ interface. The γ’2nd precipitates progressively evolve in shape from spherical to cuboidal and then to butterfly-like shapes, and the size also increases with time. After creep at 980 ℃ / 250 MPa, the creep life of two specimens was examined: one being SHT + 1100 ℃ / 30min / AC, characterized by a secondary γ’ phase, and the other being SHT without this phase. The SHT + 1100 ℃ / 30 min / AC specimen exhibited a creep life of 240 h, whereas the SHT specimen lasted for 260 h. This disparity arose from a lower density of dislocation mesh in the SHT + 1100 ℃ / 30 min / AC specimen compared to the SHT specimen, consequently reducing its creep life. Nonetheless, both durations fell within the expected normal range of variation.