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.
Highlights
The consideration of creep-fatigue interaction is becoming more and more relevant in gas turbine critical components due to the higher operational flexibility and performance required by users
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
Creep-fatigue interaction has been studied for two Ni based superalloys, one equiaxed and one single crystal, employed in critical vanes and blades of industrial gas turbines
Summary
The consideration of creep-fatigue interaction is becoming more and more relevant in gas turbine critical components due to the higher operational flexibility and performance required by users. Ni-base superalloys are mechanically strong materials that can support high mechanical stress at temperature close to their melting point. These alloys are used as structural materials of gas turbine components because they withstand strong thermal gradients due to their complex geometry, temperature distribution and intricate cooling system. The great stability of the γ /γ composite microstructure at high temperature and under the application of mechanical and thermal loading accounts for the outstanding performance of these materials in service [1, 2]. The creep-fatigue test conditions have been defined on the basis of the FE simulation of real components and the post-test inspections have been conducted to understand the physical mechanisms leading to damage development
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