Abstract:Interrupted and ruptured creep tests were conducted on single crystal superalloy DD9 at 980 °C/250 MPa and 1100 °C/ 137 MPa conditions. Microstructure evolution during creep was analyzed through scanning electron microscope and transmission electron microscope. Results show that the microstructure evolutions are similar under the creep conditions of 980 °C/250 MPa and 1100 °C/137 MPa. Cubical γ′ phase, which is dispersedly distributed in the γ matrix, gradually evolves into a layered structure perpendicular to the stress direction. The width of the γ matrix channel along the direction parallel to the stress increases. The relationship between the increase in width of the γ matrix channel and the strain satisfies linear relationship in logarithmic form, indicating that the width of the γ matrix can be deduced via the strain under creep state. This may provide an approach to investigate the width of γ matrix in single crystal superalloys during creep under high temperature and low stress conditions. In the early creep stage, dislocations formed in the γ phase generate mutually perpendicular networks through cross-slip at the γ/γ′ interface. Then, stable hexagonal dislocation networks form as a result of the coupling effects of external stress and mismatch stress at high temperatures. In the later period of creep, dislocations shear the γ′ phase, ultimately causing the fracture.