Fatigue Life Prediction of Single Crystals for Turbine Blade Applications

This paper describes a fatigue life prediction model accounting for high temperature applications of metallic materials. The formulation of the model is for general anisotropy and multiaxiality of loading. This phenomenological model distinguishes between an initiation phase and a propagation phase, and takes into account oxidation and creep effects on fatigue life. An application of the model is given for a coated single crystal superalloy for turbine blades. Model predictions are in good agreement with a large set of experimental data for mechanical loading including thermomechanical fatigue tests. A new experimental device, designed to produce a thermal gradient in the thickness of thin walled specimens, is also presented. This device has been used with polycrystalline and monocrystalline superalloys. Corresponding life predictions, performed by using recent anisotropic models, are presented for the single crystal superalloy.