Fatigue crack propagation at elevated temperatures (650 and 725°C) has been studied in a powder processed high strength nickel based superalloy, U720Li, in air and vacuum environments, using trapezoidal loading waveforms. Constant load (increasing D K) tests were used to generate da/dN ± D K curves, while interrupted constant D K tests were used to study crack propagation paths and mechanisms. At 650°C in air there is little effect of any dwell at maximum load while at 725°C such a dwell causes a signi® cant increase in the crack growth rate coupled with a transition from mixed mode to fully intergranular crack growth. In vacuum the growth rates were signi® cantly lower, and the dwell caused little or no change in crack growth rate at 650°C, but an increase at 725°C. The crack path in vacuum changed from fully transgranular at 650°C to incorporate increasingly mixed mode growth at 725°C with dwell. The intergranular failure in vacuum was through creep cavitation of grain boundaries, while in air, static failure of oxygen embrittled boundaries dominated.MST/4835
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.