High Cycle Fatigue of Nickel-based Superalloy MAR-M 247 at High Temperatures

AbstractThe nickel-based superalloy MAR-M 247 was experimentally studied in the area of high-cycle fatigue at temperatures 650, 800 and 900°C. The alloy, a cast polycrystalline material processed by hot isostatic pressing (HIP), was subjected to symmetrical cyclic loading. The fracture surfaces of specimens were studied by scanning electron microscopy from the perspective of the influence of temperature on the fatigue damage mechanism and fatigue crack initiation. The extent of Stage I of crystallographic fatigue crack propagation and non-crystallographic Stage II differs with various test temperatures. Fatigue crack initiation sites were predominantly shrinkage pores inherited from casting. The general description of governing mechanisms of the fatigue crack initiation and the crack propagation are proposed