The effects of temperature and stress on the high-cycle fatigue properties of a Ni-based wrought superalloy

The high-cycle fatigue behavior of the wrought superalloy GH4742 was studied at room-temperature (RT), 650 °C and 750 °C. The fatigue strength at 10⁷ cycles of the GH4742 alloy increases with increasing temperature, which is mainly due to the different fracture modes at different temperatures. Fatigue cracks at room temperature originate from the specimen surface, including surface inclusions, surface carbides, surface slip and surface crystallographic facets. At 650 °C and 750 °C, the fatigue crack initiations originate from the subsurface or internal crystallographic planes under lower stress levels, while the surface defects or surface crystallographic planes originate under higher stress levels. The dislocation density of the GH4742 superalloy is low at room temperature and 650 °C, and the deformation mechanism is mainly governed by APBs shearing primary γ′ and Orowan bypassing secondary and tertiary γ′. When the temperature rises to 750 °C, the deformation mechanism is mainly governed by stacking faults shearing primary, secondary and tertiary γ′. Furthermore, antiphase boundaries (APBs) shearing primary γ′ and Orowan bypassing secondary and tertiary γ′ occur.