Investigations on cyclic deformation behaviors and corresponding failure modes of a Ni-Based superalloy

Abstract

High cycle fatigue properties with different stress levels were performed on GH4742 alloy at room temperature (RT) and 750 °C by staircase method. Comparative analyses of failure mode were made at the two different temperatures. The results show that failure mode changes gradually from surface defects failure to interior crystallographic facets failure with increasing temperature. Meanwhile, at 750 °C, the majority of specimens present crystallographic facets failure, while only three of initiations with higher stress level are associated with surface inclusions. The reasons for surface defects initiations are related to local stress concentration under lower temperatures or higher stress levels. The effects of competing failure modes on fatigue properties, including fatigue life and fatigue damage rate, were discussed in detail, which is consistent with the results fitted by Basquin relationship. Transmission Electron Microscope observation reveals that γ′ particles are sheared by dislocations at RT, whereas at 750 °C, climbing, bypassing and shearing mechanisms operate simultaneously, which is due to the higher thermal activation energy and stacking fault energy at 750 °C.