Microstructurally-Informed Life Prediction Modeling of Combined High-Cycle Fatigue and Creep in a Ni-base Superalloy

Abstract

The capability to accurately predict creep and high-cycle fatigue (HCF) lifetime is crucial to the successful design of an industrial gas turbine. In particular, turbine blades are subjected to extreme environments, where elevated temperatures and an array of mechanical and dynamic loads are present. Increased temperatures and aggressive designs are needed to meet next-generation efficiency and power output targets, further intensifying blade loading conditions and enabling new life-limiting concerns, such as the interaction of HCF and creep. The interaction of HCF and creep has not been fully investigated, and is not adequately captured in existing life prediction models. This lifing capability is needed to maintain current reliability standards in next-generation industrial gas turbine blades.The life-limiting interaction of creep and HCF is explored in this study using standard and pre-crept test specimens of a conventionally cast Alloy 247 LC material subjected to high temperature, high frequency loading until failure. The experimental data are obtained for two temperatures, three stress ratios, and a range of pre-creep strains, providing a comprehensive survey of synchronous and stepwise interactions. A microstructurally-informed life prediction model is created by leveraging existing principles with the experimental results and the findings of from a thorough post-test failure analysis.