The creep deformation behavior of a single-crystal Co-Al-W-base superalloy at 900 °C

The creep deformation behavior of a single-crystal Co-Al-W-Ni-Cr-Ta alloy with low tungsten content has been studied at stresses between 275 and 310 MPa at 900 °C. The alloy exhibits comparable creep strength with that of Co-Al-W-base alloys containing more tungsten. The creep deformation consists of three stages, the primary stage, the steady-state stage and the tertiary stage, when described by the creep strain rate versus time curve. At 900 °C, γ′ precipitates tend to raft along the direction of applied tensile stress in the steady-state creep stage and a topologically inverted and rafting γ/γ′ microstructure is formed in the tertiary stage. The main deformation mechanism in the primary creep stage is dislocation shearing of γ′ precipitates, and in the following creep stages, the dominant deformation mechanism is dislocations bypassing γ′ precipitates.