Crack Growth Under Isothermal and Thermomechanical Fatigue and Dominant Failure Mechanisms in Heat-Resistant Alloy

This study presents an analysis of crack growth rates and an assessment of fracture mechanisms based on experimental data on isothermal and non-isothermal fatigue. The test results were obtained in the temperature range of 400-650°C under conditions of harmonic fatigue, creep-fatigue interaction, in-phase and out-of-phase thermomechanical cyclic loading. The object of the study was the heat-resistant nickel-based alloy EI698. After testing, the specimens underwent detailed fractographic analysis using scanning electron microscopy. It was found that, in terms of crack growth acceleration, the fatigue fracture diagrams follow this order: isothermal creep-fatigue interaction, non-isothermal in-phase thermomechanical fatigue, isothermal pure fatigue, and non-isothermal out-of-phase thermomechanical fatigue. The arrangement of the crack growth rate curves corresponds to the dominant intergranular and transgranular fracture mechanisms, and the features of their changes have been identified.