Effects and mechanisms of low cycle fatigue and plastic deformation on subsequent high cycle fatigue limit in nickel-base superalloy Udimet 720

The effects and mechanisms of low cycle fatigue (LCF) on subsequent high cycle fatigue (HCF) limit were investigated in nickel-base superalloy Udimet 720 at room temperature at a stress ratio of 0.1 and frequencies of 1 and 25 Hz for LCF and HCF, respectively. The HCF limits were determined after various fractions of LCF life consumption. Results show that small fractions of LCF life consumption significantly reduce the subsequent HCF limit, and the reduction is attributed to a combination of LCF damage and the plastic deformation induced during the LCF process. Microstructural characterization indicates that both LCF and plastic deformation reduce the HCF limit by activating the slip systems in the FCC structure of the material, creating favorable sites for easy subsequent HCF damage.