Creep-fatigue interactions in equiaxed and single crystal Ni-base superalloys

Abstract

Abstract. Ni-base superalloys are employed as structural materials for the most critical hot gas path components of gas turbines. The current market requirement is to cycle the machine every day, providing energy when it is most needed. It is therefore important to understand how creep and fatigue damages interact in these components. Starting from a significant knowledge base of mechanical and microstructural behaviour established from standard tests of the equiaxed and single crystal superalloys, creep-fatigue tests have been performed to evaluate how the two damage conditions develop together. The creep-fatigue testing conditions represent the maximum temperature and strain at the critical locations in real components, while the position of hold-time has been varied from tensile to compressive to understand the effect on reduction in crack initiation endurance with respect to standard LCF tests and on the microstructural mechanisms. The experimental test results have been explained in terms of microstructural evolution and they have been correlated to that observed at critical locations in real components.