Optimization of Secondary Crystallographic Orientation of Ni-based superalloy single crystals

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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, (-111)[1-12] slip system is result of pass of intrinsic-extrinsic superlattice stacking faults pair through the γ phase. In the tensile orientation close to [011], (111)[-211] slip is occurred by twinning shear through γ and γ' phases. In the case of creep strength, the results were in agreement with the assumption of the operation of the {111}<112> slip in the primary creep and {111}<101> slip in the secondary creep. The n … More otched creep behavior was found to be influences by the additional aging at 850℃ 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.We report some preliminary results of a systematic study of the stress dependence of primary creep in three alloys: TMS82+, CMSX-4 and TMS 75, containing 2.4, 3.0 and 5.0 wt % Re respectively. Creep tests were performed at a range of stresses on specimens cut from a single bar; orientations between 8-12° from [001] were chosen to promote a reasonable amount of primary creep and provide consistency in orientation across the series of alloys. It has been found that the amount of primary creep increases as the amounts of rhenium and cobalt in the alloys increase, and for each alloy a stress threshold for the occurrence of a distinct regime of primary creep is identified. TEM observations of the dislocation mechanism of deformation show a higher occurrence of stacking fault shear with increasing primary creep. Considerable differences in the extent of dislocation penetration into the γ phase and in the configuration of the mobile dislocation ribbons point to a combination of factors governing mobility and hardening being responsible for high primary creep. Less