High temperature shakedown of a 2nd generation nickel-base single crystal superalloy under tension-torsion loadings

Abstract

Components that face aggressive thermomechanical loadings that are cyclic and multiaxial often employ nickel-base single crystal superalloys to achieve acceptable lifetimes. These superalloys are commonly used with first-yield design rules, however their use under inelastic design, leveraging safe elastoplastic shakedown behaviors at elevated temperatures, has remained largely unexplored. This paper is the first to combine cyclic test results with some microstructural observations to establish conditions for the macroscopic shakedown response of a 2nd generation nickel-base single crystal superalloy under tension-torsion loadings at 600 °C. Microstructural studies are performed to identify and compare deformation mechanisms in specimens that exhibit shakedown and ratchetting. Based on the results, directions for future materials development, to directly exploit shakedown in design, are suggested.