Investigation of Fatigue Small Crack Propagation Behavior in Superalloy FGH96 under Different Stress Ratios

The characteristic analysis of fatigue small crack propagation behavior of superalloy FGH96 in a plane stress state was carried out based on a series of in situ scanning electron microscope fatigue tests. The influence of microstructure on fatigue small crack propagation behavior of superalloy FGH96 under the different stress ratios was investigated. The results indicated that the fatigue small crack growth rates showed obvious dependence on stress ratios, following as R = 0.5 > R = 0.2 > R = 0.1. Fatigue small crack propagation behavior of superalloy FGH96 occurred preferentially plastic slipping on grains surface and then resulted in a mixed model of intergranular and transgranular fracture during the fatigue small crack evolution. The effects of microstructural inhomogeneities (e.g., grain boundaries, defects, crystal orientation) on deflection and branching of fatigue small crack propagation were also evaluated.