Effect of shaped film cooling hole manufacturing defects on the high
cycle fatigue behavior of a Ni-based single crystal superalloy
Abstract
The complex geometrical configuration of shaped film cooling holes
(FCHs) enhances the cooling efficiency of turbine blades, while the
stress concentration at the shaped FCH edge and the manufacturing
defects usually leads to high cycle fatigue (HCF) failure under the
service conditions. In this study, HCF tests at 900 ℃ were conducted on
DD6 single crystal superalloy containing dustpan and dovetail FCHs. The
effect of shaped FCHs and manufacturing defects on the HCF strength was
investigated, and the related HCF failure mechanism was analyzed using
SEM, EDS and EBSD. The results show that manufacturing defects including
pores, recast layer and polycrystalline microstructure region exist
around the shaped FCH edge. The stress concentration of defective pores
promotes the plastic deformation and oxidation at high temperatures,
leading to crack initiation. The fatigue strength is 318.89 MPa for the
dustpan FCH specimen and is 304.93 MPa for the dovetail FCH specimen,
and both of them are lower than that of the traditional cylindrical FCHs
due to the existence of the manufacturing defects, indicating the
necessity to consider the effect of manufacturing defects in the
evaluation of the HCF strength of components with the shaped FCHs.