Effects of Crystal Orientations on the Low-Cycle Fatigue of a Single-Crystal Nickel-Based Superalloy at 980 °C

The influence of crystal orientations on the low-cycle fatigue (LCF) behavior of a 3Re-bearing Ni-based single-crystal superalloy at 980 degrees C has been investigated. It is found that the orientation dependence of the fatigue life not only depends on the elastic modulus, but also the number of active slip planes and the plasticity of materials determine the LCF life, especially for the [011] and [111] specimens. The [011] and [111] specimens with better plasticity withstand relatively concentrated inelastic deformation caused by fewer active slip planes, compared to the [001] specimens resisting widespread deformation caused by a higher number of active slip planes. Additionally, fatigue fracture is also influenced by cyclic plastic deformation mechanisms of the alloy with crystal orientations, and the [001] specimens are plastically deformed by wave slip mechanism and fracture along the non-crystallographic plane, while the [011] and [111] specimens are plastically deformed by planar slip mechanism and fracture along the crystallographic planes. Moreover, casting pores, eutectics, inclusions and surface oxide layers not only initiate the crack, but also reduce the stress concentration around crack tips. Our results throw light upon the effect of inelastic strain on the LCF life and analyze the cyclic plastic deformation for the alloy with different orientations.