Influence of primary crystal orientation on deformation and crack nucleation around dense film cooling holes in Ni-based single crystal superalloy

The influence of primary crystal orientation on deformation and microcrack nucleation behavior around dense film cooling holes (FCHs) in Ni-based single crystal thin-walled plate are investigated based on in situ tensile tests, multi-level characterization and crystal plastic finite element method (CPFEM). Difference of mechanical behavior, slip deformation and crack formation pattern between two special crystal orientations are revealed. Results show that the [111] oriented specimens have a less deformation and simpler fracture path than the [011] oriented specimens, but their yield strength is higher. The different of slip systems activation between two crystal orientations is implemented by CPFEM. Combined the atomic force microscope (AFM) characterization, the slip bands intensity along the [011] and [111] crystal orientation is quantified. The crack initiation threshold stress of the [111] orientation is higher than that of [011] orientation. Microcracks start to form along the slip bands at the position around the FCH where the cumulative shear plastic strain was greatest. The predicted slip bands and crack nucleation obtained from CPFEM simulations show good agreement with experimental observations. The dislocation structure at crack tip plastic zone of two orientation is revealed. The [011] orientation demonstrates a more homogeneous dislocation shearing of the γ/γ' phase compared to the [111] orientation, indicating a more uniform plasticity and crack resistance.