Fatigue life evaluation of a single crystal Ni-base superalloy, accompanying with change of microstructural morphology

A new micromechanics model was proposed to estimate the effects of microstructural geometry on fatigue life of single crystal Ni-base superalloys. The Eshelby’s theory, the averaging field approximation and the hybrid composite theory were combined and extended so that it makes possible to discuss many types of microstructural factors: volume fraction of γ′ precipitates, γ/γ′ lattice misfit, and inhomogeneities between γ/γ′ phases against elastic or plastic deformation. The presented method can be applied to such a material system in which the γ/γ′ morphology is changed during the cyclic loading at high temperature. The numerical calculations demonstrated that the plate-type rafted structure perpendicular to uni-axial stress direction may have detrimental effect on the isothermal fatigue strength for negative misfit superalloys.