Effect of Grain Size on Low Cycle Fatigue Life in Compressor Disc Superalloy GH4169 at 600 °C

Nickel-based superalloy GH4169 in Chinese series (similar to Inconel 718 in the U.S. and NC19FeNb in France) has been widely used for aero-engine discs due to its excellent fatigue, oxidation and corrosion resistance at high temperature. The effect of grain size on the low cycle fatigue (LCF) lifetime was investigated in this study. Smooth specimens cut from an actual compressor disc in a civil aero-engine were conducted to strain-controlled LCF tests at 600 °C, and results showed a significant scattering in the LCF lifetime. Then grain sizes of specimens were estimated using optical microscope (OM) and Image-Pro Plus (IPP) software. A negative correlation between the grain size and LCF lifetime was found by inducing the grain refinement strengthening theory. Afterwards, a modified Smith-Watson-Topper (SWT) model was developed to describe the dependence of LCF lifetime on grain size. Finally, the possible microscopic mechanism of the grain size-dependent LCF behavior of GH4169 superalloy was discussed based on fracture analysis.