Dwell-fatigue crack growth behavior of FGH4108 alloy at high temperature

Fatigue crack growth experiments and interrupted tests are conducted on the fourth-generation powder metallurgy superalloy FGH4108 under varying temperatures and dwell time. The influence of temperature and dwell time on crack growth behavior is analyzed using characterization techniques such as Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and Electron Probe Microanalysis (EPMA). The mechanism by which oxidation damage affects crack growth is revealed. A fatigue crack growth rate model describing the mechanical-oxidation coupling effect is proposed. The results show that as temperature and dwell time increase, the crack growth rate rises and fatigue life decreases significantly. Fractographic analysis reveals that at 650 ℃, fatigue cracks primarily propagate transgranularly with relatively flat fracture surfaces, while at temperatures above 750 ℃, fatigue cracks mainly propagate intergranularly, accompanied by the formation of secondary cracks. Concurrently, phenomena such as alterations in crack tip morphology and oxide formation were observed during crack propagation, elucidating the impact of oxidation on crack growth. The proposed model can better describe the fatigue crack growth rate at different temperatures and dwell time. At the same time, the effects of mechanical damage and oxidative damage on crack growth are decoupled, and the temperature dependence of oxidative damage parameters is determined.