Accelerated damage mechanisms of aluminized superalloy turbine blades regarding combined high-and-low cycle fatigue

Accelerated fatigue failure mechanisms of aluminized Ni-based superalloy turbine blades are the focused in this paper. The qualitative and quantitative analyses on the fracture appearances and microstructures of the field-serviced and lab-tested turbine blades were conducted, and a ‘micro-defect transfer mechanism’ is finally raised and elucidated regarding the combined high-and-low cycle fatigue (CCF). The CCF tests are performed on the Ni-based superalloy turbine blades with aluminized coatings in three acceleration states. Then, the fracture morphologies are inspected to confirm the dominant sources of crack initiations under different accelerated loads. It illustrates that: the cracks mainly generate from the interface in the slow acceleration state, which is similar to that in the service state. While, the surface and interface cracking collaborates in the fast acceleration state, as the surface cracking turning to be the dominant factor. Furthermore, to interpret the essential mechanisms of fatigue failures of the aluminized turbine blades, the qualitative and quantitative analyses are carried out on the cross-sectional microstructures and elemental compositions jointly assisted by advanced intelligent algorithms, which can assist to better identify and extract the valid information in the microscopic images. Ultimately, the micro-defect transfer mechanism is proposed and elaborated in detail for revealing the fatigue failure mechanisms of aluminized turbine blades in different acceleration states.