Investigation of Crystallographic Influences on Small Fatigue Crack Growth in Powder Metallurgy Superalloy FGH96

In situ small fatigue crack growth experiments at 500°C, combined with pretest and posttest electron backscatter diffraction analysis, were conducted to investigate the growth behavior of FGH96. High-temperature fatigue loading reduced the average texture intensity and induced a pronounced {111} plane normal alignment along the loading direction, forming a localized strong texture. Significant local lattice rotations and geometrically necessary dislocation accumulation occurred in the crack region, both decreasing with distance. Crack growth was predominantly transgranular and strongly influenced by crystallographic orientation. Intragranular crack path deflection occurred with similar frequencies toward slip systems of higher and lower Schmid factors. The experimental results demonstrated that under certain conditions, high-angle grain boundaries substantially impeded transgranular crack propagation. Three types of crack growth resumption behaviors induced by grain boundaries were identified. Overall, crystallographic orientation and grain boundaries jointly govern the small crack growth. These findings enable high-precision life prediction of small fatigue cracks.