Structure Evolution and Creep Behavior for a Nickel-Base Single Crystal Alloy along [011] and [001] Orientations

The morphology evolution and creep behavior of γ′ phase in [001] and [011] oriented specimens of a nickel-base single crystal superalloy during the tensile creep at 1253 K and 200 MPa were investigated. SEM and TEM observation shows that the direction coarsening of precipitates is highly dependent on the crystal orientation. In [001] orientation, the γ′ phase transits from original cuboids to the raft-shape along the perpendicular direction to the tensile stress axis while in [011] orientation the γ′ phase develops along the [010] and [100] and evolves into a raft with inclined 45° angle to the tensile stress axis. The strain rates for [001] and [011] orientations are almost equal at the earlier stage of creep. With the matrix channel broadening, the strain rate for [011] orientation increases gradually, while the creep strength decreases rapidly. Based on the evolutional rule of γ′ phase and the creep curves, the anisotropic creep behavior is obvious at the later stage of steady-state and the tertiary creep stage