SUMMARY

Due to the extreme operating conditions present in the combustion sections of gas turbines, blades must retain substantial strength and resistance to fatigue, creep, and corrosion at high temperatures. Directionally-solidified (DS) nickel-base superalloys have been used extensively for this purpose. As costly product inspection and refurbishment is a significant drain on the resources of turbine producers, a premium is placed on accurate life prediction as the foundation of viable long-term service contracts with customers. In working towards that end, this work characterizes the behavior of the blade material CM247LC DS subjected to a variety of in-phase (IP) and out-of phase (OP) thermomechanical fatigue tests. This study consisted of an experimental phase as well as a numerical modeling phase. The first involved conducting high temperature thermomechanical fatigue (TMF) tests on both smooth and notched round-bar specimens to compile experimental results. Tests were conducted on longitudinal and transverse material grain orientations. Damage is characterized and conclusions drawn in light of fractography and microscopy. In addition, the influences of microstructure morphology and environmental effects on crack initiation are discussed. The modeling phase utilized various finite element (FE) simulations. These included an anisotropic-elastic model to capture the purely elastic notch response, and a continuum-based crystal visco-plastic model developed specifically to compute the material response of a DS Ni-base superalloy based on microstructure and orientation dependencies. Finally, life predictions using simple and complex analytical modeling methods are discussed for predict ing component life at various stages of the design process.