Research on recrystallization and crack fracture of single crystal turbine blade

The cracks were found on the surface of DD6 single crystal turbine blade. The blade fracture mode and causing reason were studied by analyzing the fracture surface and the microstructure in the vicinity of the cracks using Optical Microscope (OM) and Scanning Electron Microscope (SEM). The results indicated that the cracks fracture was resulted from the surface recrystallization of the blade. Owing to the presence of cast stress in the blade during the directional solidification process, a later solution treatment resulted in the formation of recrystallization grains. Meanwhile, some white particles with high concentration of W were precipitated at the grain boundary. Under the testing condition, the cracks initiated at the recrystallization boundary and expanded along the white precipitated phases until fatigue fracture.