| Abstract Scope |
One key performance attribute of cases and seals in advanced gas turbine engines is resistance to thermal fatigue, which is dictated by strains associated with thermal cycling of the component and the material’s intrinsic resistance to fatigue crack initiation and propagation. Frequently isothermal strain-controlled low-cycle fatigue (LCF) testing is utilized to assess the candidate alloys’ intrinsic fatigue 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 Waspaloy, 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 fatigue lives, within experimental scatter, but the 244 alloy deformed by deformation twinning, whereas Waspaloy deformed by dislocation slip and precipitate shearing and looping. |