Fatigue fracture mechanism and life prediction of nickel-based single crystal superalloy with film cooling holes considering initial manufacturing damage

Abstract

Film cooling holes (FCHs) in nickel-based single crystal superalloy turbine blades are critical yet fracture-prone regions, where assessing initial manufacturing damage and predicting fatigue life remain significant challenges. This study employs the equivalent initial flaw size (EIFS) model to evaluate initial damage in FCH structures and introduces a probabilistic fracture mechanics framework for fatigue life prediction. A 3D helical fluid dynamics model is developed to compute temperature and stress fields at FCH edges. A multi-angle rotatable 3D XRD device measures six interplanar spacings, enabling residual stress assessment in FCH micro-regions and validating manufacturing simulations. By quantifying geometric, metallurgical, and mechanical parameters, the initial damage state of FCHs is characterized. The EIFS strategy, applied via the time to crack initiation (TTCI) method, comprehensively quantifies this damage. The study investigates fatigue fracture mechanisms, proposes a unified crack extension driving force (ΔM_eff), and develops a probabilistic fracture mechanics model. Using the “double 95″ EIFS (EIFS_95/95) within probabilistic crack propagation rates, the fatigue life of FCHs at 850 °C is predicted and experimentally validated. Results reveal that initial damage significantly influences crack initiation and propagation, with thermal damage zones exhibiting high dislocation activity and oxidation-induced γ’-free areas serving as critical crack initiation sites. The EIFS_95/95 value is calculated as 0.0429 mm, and predicted fatigue life falls within a two-fold scatter band compared to experimental data. This study successfully predicts fatigue life while accounting for initial manufacturing damage, providing a novel approach for designing FCHs with improved longevity and reliability.