Novel crack hindrance analysis, fracture behavior, and life assessment of forged GH4169 superalloy under high and very high cycle fatigue conditions

The axial loading high- and very-high-cycle fatigue tests with stress ratios of −1 and 0.1 were conducted to investigate the fracture mechanism, crack hindrance behavior, and life assessment of forged GH4169 nickel-based superalloy in combination with techniques including 2D and 3D microscopies, and electron-backscatter diffraction (EBSD). Fractographic observations reveal that surface failures are caused by surface flaws or slipping under both stress ratios, whereas internal failures are attributed to pores or cavities only at a stress ratio of 0.1. Based on the EBSD analysis of the crack hindrance phenomenon, it is observed that high-angle grains and annealing twins form a complex structure that impedes crack growth. This is evidenced by lower values of kernel average misorientation, geometric compatibility factor, and Schmid factors within the crack hindering zone. Under the influence of different stress ratios, the threshold values and transition sizes from small to long cracks are elucidated. Considering the effect of microstructural defects and stress concentration, a crack initiation fatigue life estimation model is developed, demonstrating a good resemblance between predicted and experimental results. Finally, a novel hypothesis is developed to analyze the relationship between loading and energy dissipation, potentially offering valuable insights for further research.