Low Cycle Fatigue Behavior of Single-Crystal Superalloy CMSX-4 at Different Temperatures

The low cycle fatigue behaviors of single-crystal superalloy CMSX-4 were investigated at 760 and 950 degrees C. At 760 degrees C, specimens have longer fatigue lives and higher strength under higher strain amplitude. The fracture sections of specimens at 760 degrees C have a large height difference with an angle of 45 degrees to the stress axis direction, and the cracks expand along the {111} plane. While the fracture sections of specimens at 950 degrees C are perpendicular to the stress axis, and the cracks expand along the {001} plane. Scanning electron microscope was employed to analyze the fatigue fracture, and it is found that the micropore near the surface of specimens at 760 degrees C is the main fatigue source, while the fatigue cracks originated from the oxide layer near the surface of specimens at 950 degrees C is the main fatigue source and it shows multiple sources of cracking. Transmission electron microscope was employed to analyze the dislocation motion modes. The deformation mechanism of low cycle fatigue at 760 degrees C includes planar slip and wavy slip. Whereas, the dislocation at 950 degrees C mainly moves by cross-slip and a process of gliding and climbing.