Creep-fatigue–environment interactions in INCONEL 617

Creep-fatigue testing of alloy 617 was performed in air, vacuum, and purified Ar environments at 1000 °C. Tests were performed in axial strain control at total strain ranges of 0.3% and 1.0% (fully reversed) with hold times at maximum tensile strain ranging from 0 to 1800 s. Introduction of a tensile hold period led to reduced creep-fatigue life at both strain ranges in all environments; the effect was greater at 0.3% than 1.0%. The hold time effect clearly saturated for tests at 1.0% strain range; the behavior at 0.3% was not clear. Decarburization occurred in specimens tested in vacuum and purified Ar, but not in air. Although fatigue lives were longer in the inert environments than in air for most test conditions, quantitative assessment of the differences was not possible because cracking frequently did not occur before test termination due to load drop for tests in inert environment. Cavitation damage was observed for tests with tensile hold periods in all environments.