VHCF Failure Analysis and Life Prediction of Ni‐Based Superalloy Under Different Temperatures and Stress Ratios

Nickel‐based superalloys are widely utilized in aerospace, energy, and other fields for their exceptional high‐temperature and oxidation resistance. However, in engineering, components often endure over 10 9 cycles, causing very high cycle fatigue (VHCF) failure. This study focuses on GH3625 alloy using a 20‐kHz ultrasonic fatigue system to investigate VHCF behavior, crack initiation, and propagation mechanisms at room temperature (RT) and 600°C under varied stress ratios ( R = −1, 0.2, 0.7). Results show higher stress ratios significantly reduce the fatigue limit. Moreover, the crack initiation mode transitions from single‐point surface initiation to multipoint competitive initiation, with oxidation and creep effects at elevated temperatures accelerating fracture. Energy dissipation characteristics of the material are analyzed, and an energy dissipation model is developed and applied to predict fatigue life at RT under R = −1. This research provides a novel theoretical foundation and practical engineering insights for fatigue life prediction under complex operating conditions.