Influence of primary and secondary crystallographic orientations on strengths of nickel-based superalloy single crystals

It has been revealed that the strengths of the notched specimens were affected by the crystallographic orientation not only in the tensile direction (primary orientation) but also in the thickness direction (secondary orientation). In this study, by using single crystals of an experimental superalloy which shows distinct active slip systems, the influence of primary and secondary crystal orientation on creep and fatigue strengths of Ni-based superalloy single crystals was investigated. The influence of crystallographic orientations and plastic anisotropy on the creep and fatigue strengths of single crystals of the Ni-base superalloy was discussed on the assumption that {111} <101> and {111} <112> slip systems. {111} <112> slip is unusual slip. For a tensile stress applied close to the [001] axis, ((1) over bar 11) [1 (1) over bar2] slip system is result of pass of intrinsic-extrinsic superlattice stacking faults pair through the gamma phase. In the tensile orientation close to [011], (111) [(2) over bar 11] slip is occurred by twinning shear through gamma and gamma' phases. In the case of creep strength. the results were in agreement with the assumption of the operation of the <112> slip in the primary creep and {111} <101> slip in the secondary creep. The notched creep behavior was found to be influenced by the additional aging at 850degreesC for 20 h, which prohibited activity of {111} <112> slip systems. The fatigue lifetime and crack growth behavior depended on both plastic anisotropy caused by arrangement of {111} <101> slip systems and the stress state.