Fatigue crack initiation and propagation behavior of nickel-based single crystal DD6 under different drilling processes

The fatigue crack initiation and propagation behavior of film cooling holes (FCHs) under different drilling processes are of great significance to key structural parts. In this paper, it mainly comprehensively and systematically summarized the difference in surface condition caused by different drilling processes of nickel-based superalloys combining several characterization devices and described whole process from crack initiation to fracture in detail. The in-situ fatigue crack growth test at room temperature on the plate specimens with a different drilling FCHs (EDM and LDM) made of [001] nickel-based single crystal was carried out, and proposed a comprehensive evaluation method for the crack initiation mechanism from the three dimensions of geometry, metallurgy and mechanics. The four main octahedral slip systems are proved by finite element simulation. Then, we clarified the difference of fracture surface, crack path and fracture morphology of different drillings, and the competition mechanism between crack propagation path and slip surface was investigated. Finally, a simple unified model of fatigue crack growth rate was proposed, which provides a useful crack propagation law of different drilling hole.