Fatigue Behavior of the FGH96 Superalloy under High-Temperature Cyclic Loading

Abstract

Strain-controlled low-cycle fatigue (LCF) tests and stress-controlled creep-fatigue interaction (CFI) tests on the FGH96 superalloy were carried out at 550 °C to obtain the cyclic softening/hardening characteristics at different strain amplitudes and ratcheting strain characteristics under different hold time. The failure mechanism of the FGH96 superalloy under different loading conditions was analyzed through fracture observations. The results show that the FGH96 superalloy exhibits different cyclic softening/hardening characteristics at different strain amplitudes, and the introduction of the hold time at peak stress exacerbates the ratcheting strain of the FGH96 superalloy under asymmetric stress cycles. Fracture observations show that the magnitude of the strain amplitude, high-temperature oxidation, and the introduction of the hold time will affect the mechanical properties of the FGH96 superalloy and change its fracture mode.

Study on High-Temperature Low-Cycle Fatigue Behavior of the FGH96 Superalloy Based on Internal Stress Division

“…In the previous study, our research group explained the link between the microscopic fracture mechanism and the cyclic softening/hardening behavior of the FGH96 superalloy [21]. In this section, the micro-mechanisms summarized in the previous study will be combined to analyze the different properties exhibited by the FGH96 superalloy under different strain amplitudes from the perspective of internal stress evolution.…”

“…By comparing various curves, it can also be found that with the increase in strain amplitude, the peak stress σ max in the stable section gradually increases, while the fatigue life shows a downward trend. In previous work [21], our research group carefully analyzed the different cyclic response characteristics of the FGH96 superalloy in the early cycles through the stress-strain hysteresis curves under various strain amplitudes. Next, the cyclic softening/hardening characteristics of the FGH96 superalloy in the early cycles will be analyzed from the perspective of the relationship between the half-life hysteresis curves and the uniaxial tensile curve.…”

“…However, there are few studies on the application of internal stress to the low-cycle fatigue behavior of powder superalloys, and even fewer studies on the application of internal stress to the FGH96 superalloy in the turbine disk service environment. In previous work, our research group only analyzed the cyclic softening/hardening phenomenon of the FGH96 superalloy from the perspective of microfracture mechanics [21] but did not conduct in-depth research on the impact of internal stress evolution on the cyclic characteristics of the FGH96 superalloy. Therefore, the research on the evolution of internal stress during the cyclic process is helpful to further understand the cyclic deformation characteristics of the FGH96 superalloy and is very useful for the next step of constitutive modeling of the FGH96 superalloy.…”