Thermomechanical fatigue on the nickel based single crystal superalloy DD6 with film cooling hole

Turbine blades are subjected to thermal loads and mechanical loads simultaneously occurring during operation. Thermomechanical fatigue (TMF) is a major life-limiting factor for turbine blades. Film cooling holes within the blade introduced substantial stress concentration, which could dramatically reduce the lifetime. For quantification purposes, both smooth tubular specimens and notched specimens were utilized to perform TMF experiments. Results indicated that stress and fatigue life were in a good logarithmic linear correlation when the maximum stress changes within the range of 300-500 MPa and the hole could reduce the TMF life by 82.5%. Notched specimens with 〈010〉 and 〈110〉 oriented hole were tested respectively. It was found that the hole in 〈110〉 orientation had the weakest anti-TMF ability, since its life was only 40.0% of the 〈010〉 oriented notched specimen. The effect of drilling process was also studied. The results revealed that the life of notched specimen drilled by laser was 54.0% of the notched specimen drilled by electro-streaming drilling. The crack morphology demonstrated that TMF crack initiated from the film cooling hole edge which was severely oxidized and the crack propagated along the direction perpendicular to the edge of the hole.