Creep and fatigue interaction in the PWA1484 single crystal nickel-base alloy

While methods for modeling creep behavior of single crystal turbine airfoils are generally well developed, constant load creep does not fully represent the loading conditions present in a jet engine due to cyclic loading caused by the mission profile and throttle movements. As the aerospace industry seeks to become more accurate in physics-based modeling of materials that are used in turbine blades, creep–fatigue interaction must be incorporated into characterization of turbine blade materials. PWA1484, a second generation single crystal nickel-base superalloy that is used for turbine blades in many of today's high performance jet engines was tested in a creep–fatigue environment that is meant to simulate some conditions of the service environment of a jet engine. This research explores the behavior and microstructural evolution of samples of PWA1484 tested in a creep–fatigue environment at 871 °C in air. It was found that specimens subjected to prior fatigue loading exhibit a smaller region of primary creep that is proportional to the number of prior fatigue cycles, and an accelerated transition to a tertiary creep regime. However, specimens that are subject to a static load and allowed to creep to 2.5% creep strain exhibited an un-affected fatigue behavior. Post-test microstructural analysis revealed a coarsening of the gamma prime (γ′) precipitates that was dependent on loading condition and time spent at elevated temperature.

Research highlights▶ Primary creep deformation in PWA1484 is decreased with an increase in γ′ size. ▶ Primary creep in PWA1484 is decreased by prior fatigue cycling. ▶ Tertiary creep occurs earlier in specimens subjected to considerable prior fatigue cycling. ▶ The fatigue life of PWA1484 was not affected by prior creep strains of 2.5%.