An LCF lifetime model for PM superalloy considering equivalent ellipsoidal inclusion

The non-metallic inclusions are one of the main defects in powder metallurgy (PM) superalloy, which may promote crack initiation under the cyclic loading and seriously affect the safety of aero engines. To quantify the effects of inclusions to the low cycle fatigue (LCF) lifetime, the LCF tests on PM FGH96 superalloy are firstly carried out to observe the inclusions on fracture. By equating the inclusion to an ellipsoid, the relationship between the inclusion's feature and the stress field is established based on Eshelby's theory and finite element method (FEM). Then, the ellipse-equated fracture is determined according to the maximum shear stress's location. Subsequently, key inclusion-related parameters influencing the LCF lifetime are introduced to construct a modified SWT model. Finally, the model's accuracy is validated by comparing with the LCF experimental data. It is demonstrated that the modified SWT model has a good accuracy, with an improvement of scattering band from ±15 to ±4 compared with the original SWT model.