Fatigue behavior and failure mechanism of diffusive film cooling holes considering metering angle effect

This paper investigates the effect of metering angle on high-temperature fatigue behavior and failure mechanism of Ni-based single crystal diffusive film cooling hole (FCH) fabricated by femtosecond laser. High temperature fatigue tests were conducted at 980℃/500 MPa. Experimental results demonstrated that as the metering angle of diffusive FCH increases from 30°, 40° to 50°, the fatigue life first increases and then decreases. The effect of metering angle on the fatigue fracture mechanism of diffusive FCH specimens is elucidated through variations in fracture path, surface morphology, crack initiation sites, and crack-tip microstructure. EDS and EBSD analyses further reveal the microscopic failure mechanism, oxidation behavior, and plastic deformation around the diffusive FCH. Crystal plasticity finite element method (CPFEM) was used to calculate resolved shear stresses (RSS) around the diffusive FCHs. The RSS magnitudes and distributions for the three types of diffusive FCHs correlate well with experimentally measured fatigue life and crack nucleation location. Local plastic deformation and high-temperature oxidation near the diffusive FCH together initiate fatigue microcracks. The fatigue–oxidation coupled damage model was employed to analyze the damage distribution around the diffusive FCH. The maximum damage was consistently identified at the acute-angle region of the circular hole edge. Life predictions based on the half-life concept show that the predicted life fall within a ± 2-fold scatter band of the experimental results.