Effect of Femtosecond Laser Drilling on the Fatigue Properties of the Third-Generation Single-Crystal Superalloy DD9

Film holes can effectively reduce the surface temperature of aeroengine turbine blades, but it will damage the continuous surface and have a negative impact on the fatigue performance. In this study, the effects of femtosecond laser drilling on the surface integrity and the high cycle fatigue properties of the third-generation single-crystal superalloy DD9 were investigated. After standard heat treatment, 1 row and 3 rows of holes were drilled on DD9 specimens by femtosecond laser, respectively. The shape and section structure of the holes were observed by OM and SEM. After that, the specimens with different holes were subjected to high cycle fatigue testing at 980 °C in ambient atmosphere. The results showed that femtosecond laser drilling did not produce recast layer and microcracks, and the hole wall roughness was good. However, femtosecond laser drilling had the problem of roundness and taper deviation. The fatigue limits of specimens without holes, 1 row of holes and 3 rows of holes were 500, 420 and 407 MPa, respectively. The thickness of oxide layer is about 5 μm at high stress amplitude and about 46 μm at low stress amplitude. The combined action of oxidation damage and stress concentration caused by holes leads to the difference of fatigue lives between high- and low-stress amplitude area. The results of finite element simulation analysis can well explain the reasons for the difference of fatigue properties of specimens with different holes.