Clarifying the creep deformation mechanisms of single-crystal superalloys under service conditions is crucial for the life assessment and performance enhancement of advanced turbine blades. To this end, this study systematically investigates the creep behavior and deformation mechanisms of two representative second-generation single-crystal superalloys(DD419 and DD5 alloys) under their respective near-service conditions through interrupted creep tests. The results show that the fracture life is 280 h for DD419 at 980 °C/250 MPa and 60 h for DD5 at 1093 °C/158 MPa, and the strain-time curves exhibit typical three-stage creep behavior, consisting of primary, steady-state, and tertiary stages. Microstructural observations reveal that N-type rafting of the γ′ precipitate occurs in DD419 alloy after creep for 100 h, while it occurs in DD5 alloy after creep for 5 h. The onset of the steady-state stage is characterized by the formation of γ′ rafting and dense dislocation networks at the γ/γ′ interfaces. The minimum creep rates during this stage are 3.2 × 10 -3 s -1 for DD419 and 1.8 × 10 -2 s -1 of the latter, and the dislocation network of the latter is denser than that of the former. In the accelerated creep stage, the microstructure evolves through extensive shearing of the rafted γ′ phase by a⟨110⟩ type superdislocations, accompanied by topological inversion in both alloys. The underlying deformation mechanisms are thoroughly elucidated, and the Burgers vectors of the superdislocations are determined via two-beam diffraction analysis. This work provides theoretical insights beneficial for the performance evaluation and service life assessment of these two single-crystal superalloys.
Wang et al. (Sun,) studied this question.