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

Components that face aggressive thermomechanical loadings that are cyclic and multiaxial often employ nickelbase single crystal superalloys to achieve acceptable lifetimes. These superalloys are commonly used with firstyield 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 degrees 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.

Automated summary

This paper combines cyclic test results with microstructural observations to establish the conditions for macroscopic shakedown response of a second generation nickel-base single crystal superalloy under tension-torsion loadings at 600 degrees C. The deformation mechanisms in specimens exhibiting shakedown and ratchetting are identified and compared. Directions for future materials development to directly exploit shakedown in design are suggested.