Effects of tensile/compressive creeps on microstructure evolution of nickel-based single crystal superalloys

The microstructure evolution and failure mechanism of nickel-based single crystal DD9 under tensile and compressive creeps at 1100 °C and 140 MPa were studied. N-type rafting occurs in tensile creep and P-type rafting occurs in compressive creep. The γ′ phases gradually roughen into a layered plate structure during tensile creep and a rod structure during compressive creep. The rafting rate of tensile creep is higher than that of compressive creep. The crystal orientation deflection affects the Schmid factor, the activating of slip systems, and the morphology of Topological Close-Packed (TCP) phases. The moving direction and morphology of dislocations between tensile creep and compressive creep are approximately “opposite”. Moreover, the microstructure evolution displays tension-compression asymmetry. The crack initiates and propagates easily along the TCP phase and the γ/γ′ interface under the combination of misfit stress and dislocation pile-up stress.