Morphology Evolution and Probability Characteristic of γ' Phase in Single Crystal Superalloy during Creep Rafting

Ni-based single crystal (SC) superalloys are widely applied in the turbine blades of advanced aero-engine due to their excellent heat resistance. Rafting is a major degradation mode of SC under creep damage. In this study, the morphology evolution and probability characteristic of shape parameters are investigated for cuboidal γ´ phase during creep rafting. Three groups of SC creep tests are carried out at 850 °C and 600 Mpa along [001] direction. Scanning electron microscope (SEM) is used to observe the microstructure of SC at four different creep times including 0 h, 8 h, 16 h and 64 h. In addition, an image processing program is developed to identify the length (normal to uniaxial stress) and width (parallel to the stress) of each γ´ phase. Two interesting findings of this investigation can be summarized as: 1) During the N-type rafting of SC, the vertical matrix channel widths are gradually decreased, and the γ phases near the vertex of the cuboidal γ´ phases disappear 2) The length, width of γ´ phases both obey lognormal distributions during creep rafting, and the standard deviations change slightly for the width, but increase significantly for the length. These above findings are of significance to multi-scale probability modeling for creep deformation and fracture.