Experimental investigation on low cycle fatigue properties of GH3536 alloy with film cooling holes in different drilling processes

Low cycle fatigue tests were carried out on thin-walled flat specimens with 14 inclined film cooling holes, using tension cycling under stress control conditions (stress ratio R = 0.1) at 850 °C. The specimen material is GH3536, a kind of Cr and Mo solid solution strengthened with high iron content of nickel-based superalloy, and the film cooling holes were fabricated by forming EDM and high-speed EDM. Comparative analysis of the differences between fatigue life and microscopic fracture morphology were conducted due to the different drilling processes. It is shown that under the same test condition, the average fatigue life of forming EDM specimens and high-speed EDM specimens reach 27 h and 20 h respectively. In other words, the former has better anti-fatigue property. Scanning electron microscope (SEM) analysis of the fracture revealed that the crack initiated from the film cooling holes and all of the fractures were oxidized seriously. However, more crack sources and tiny processing cracks were found in high speed EDM drilling specimens than in the forming EDM ones. Finite element analysis indicates that the existence of film cooling holes causes significant stress concentration.