Low cycle fatigue behaviors of single-crystal superalloy CMSX-4 at different temperatures

Abstract:

The low cycle fatigue behaviors of single-crystal superalloy CMSX-4 were investigated at 760 °C and 950 °C. At 760 ℃, specimens have longer fatigue lives and higher strength under higher strain amplitude. The fracture sections of specimens at 760 ℃ have a large height difference with an angle of 45° to the stress axis direction, and the cracks expand along the {111} plane; while the fracture sections of specimens at 950 ℃ 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 ℃ is the main fatigue source, while the fatigue cracks originated from the oxide layer near the surface of specimens at 950 ℃ 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 ℃ includes planar slip and wavy slip, which is the process of transition from planar slip to wavy slip. Whereas, the dislocation at 950 ℃ mainly moves by cross-slip and a process of gliding and climbing.

Key words:single-crystal superalloy; low cycle fatigue; fatigue fracture; dislocation