Low-Cycle Fatigue Performance and Associated Deformation Mechanisms of HAYNES® 244® Alloy and Waspaloy

One key performance attribute of cases and seals in advanced gas turbine engines is resistance to thermal fatigueFatigue, which is dictated by strains associated with thermal cyclingThermal cycling of the component and the material’s intrinsic resistance to fatigueFatigue crack initiationCrack initiation and propagation. Frequently isothermal strain-controlled low-cycle fatigueFatigue (LCF) testing is utilized to assess the candidate alloys’ intrinsic fatigueFatigue capabilities. In addition, a low coefficient of thermal expansion (CTE) is desirable since the CTE largely controls, for a given thermal cycle, the magnitude of the thermally induced strains. The primary aim of this study was to compare the LCF performance of recently developed low CTE, high strength HAYNES® 244® alloy to that of WaspaloyWaspaloy, a legacy case alloy, from room temperature to 1400 °F (760 °C). A secondary aim was to shed light on the active deformation and damage mechanisms in these alloys. We observed that both alloys exhibited comparable fatigueFatigue lives, within experimental scatter, but the 244 alloy deformed by deformation twinning, whereas WaspaloyWaspaloy deformed by dislocation slip and precipitatePrecipitates shearing and looping.