Creep rupture mechanism and microstructure evolution around film-cooling holes in nickel-based single crystal superalloy specimen

The fracture mechanism and microstructure evolution around film-cooling holes in a nickel-based single crystal superalloy specimen under tensile creep at high temperatures were investigated using thin-walled plate specimens with close-packed film-cooling holes. The results demonstrated that the film-cooling hole structure has a weakening effect on the specimen for the creep life and creep ductility. In the specimen with the film-cooling holes, a large number of small cracks formed from initial cracks along the direction of the maximum resolved shear stress during the high-temperature creep process, and the cracks propagated along the direction perpendicular to the loading stress direction. Further, the microstructure evolution of the gamma' phase around the edge of the film-cooling holes was closely related to the local stress. While N-type rafting occurred in the high-stress zone, no significant change of microstructure was observed in the low-stress zone. Further, a modified damage model of the crystal plasticity theory was used to simulate the deformation of the specimen with cooling holes under multi-axial stress state, and the results of finite element analysis (FEA) agreed with both the test results and fracture morphology.