Microstructural evolution of a directionally solidified nickel-base superalloy during thermal fatigue

The transition of γ′ phase and dislocation during thermal fatigue test was investigated. There is γ′ denuded region in two sides and the tip of thermal fatigue crack because of oxidation during thermal fatigue test. γ′ phase coarsens and rafts. The direction of γ′ rafting is perpendicular to the orientation of crystal growth. High density dislocations are found near crack. Single dislocation moves in the matrix apart from crack. A few dislocations shear γ′ phase because of relatively low strength of γ′ phase at high temperature.