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.