Development of creep-dominant creep-fatigue testing for Alloy 617

Alloy 617’s resistance to creep, fatigue and oxidation damage makes it suitable for structural applications at high temperatures (800-1000°C). Existing experimental techniques for investigating the creep-fatigue response use strain-based cyclic loading with a dwell time to generate varying portions of fatigue and creep damage respectively. Due to rapid stress relaxation of Alloy 617 at high temperatures, strain-based creep-fatigue testing only generates fatigue-dominant damage. Tests that produce creep-dominant damage are therefore essential to fully understand the creep-fatigue interaction for this alloy. Designing creep-dominant creep-fatigue tests is a challenging task due to large inelastic strains produced at high temperatures. Thus, multiple testing profiles must be examined to achieve this goal. This paper presents the stress-strain curves and experimental observations for various testing profiles and also discusses the microstructural aspects of the failed specimens. The authors propose a new loading profile that produces a larger fraction of creep damage thereby completing the failure envelope of Alloy 617 on a creep-fatigue interaction diagram.