High cycle fatigue in a single crystal superalloy: Time dependence at elevated temperature

Abstract

The airfoil sections of turbine blades in aircraft engines are subjected to very high temperatures, high stresses, and aggressive environments. These factors can lead to fatigue behavior that is quite complex, and dependent on stress level (both alternating and mean) and creep and environmental effects. This paper examines the high cycle fatigue (HCF) behavior of a single crystal superalloy, PWA1484™ coated with a platinum aluminide environmental coating, at elevated temperature, 1038°C (1900°F), and identifies the time dependent creep and oxidation interactions of this alloy under high frequency fatigue cycling. Two major modes of failure were observed, fatigue at low mean stress, and stress rupture at higher mean stress. The capability of these basic modes were modeled separately and then combined into a damage summation model that was used to successfully describe the HCF capability under more complex cyclic conditions more representative of turbine engine conditions.