Temperature Effect-Related High and Very High Cycle Fatigue Failure Analysis and Life Estimation of Forged Superalloy

To analyze the temperature effect-related failure behavior and estimate the fatigue life of forged superalloy, high- and very-high-cycle fatigue experiments were performed. The microstructural characteristics, failure modes, and crack growth behavior are characterized by two- & three-dimensional microscopy techniques, along with electron-backscatter-diffraction (EBSD) analysis. The fractographic analysis demonstrated that surface failure at both 25 °C and 650 °C is attributed to surface flaws, whereas subsurface and internal failures are primarily driven by faceted cracking, often facilitated by inclusions or pores at 25 °C, and solely assisted by large grains at 650 °C. EBSD analysis revealed that crack propagation occurs in a transgranular manner, leading to the formation of facets; however, it is impeded by a complex structure comprised of high-angle grain boundaries and twin boundaries. In addition, under the influence of both temperatures, the threshold values for small as well as long cracks are elucidated. Finally, a fatigue life assessment approach that accounts for primary defects and different temperatures is established, and the prediction results demonstrate a closer alignment with the experimental data.