Corrosion-fatigue testing of Ni-based superalloy RR1000

Abstract

Operation of gas turbines at high temperatures can lead to corrosion of turbine materials. A programme was designed to understand the corrosion-fatigue behaviour of two grain size variants of RR1000 under cyclic loading at elevated. Tests were conducted on cylindrical specimens under a range of loading conditions. Results indicated that salted specimens tested in air-SO x had shorter fatigue lives than unsalted specimens tested in air, and this deficit was dependent on stress and/or test duration. Examination of specimens showed that the extent of corrosion was dependent on exposure time and stress. Additional salt loading resulted in faster initial pit growth which led to lower fatigue lives at higher stresses. This paper is part of a thematic issue on the 9th International Charles Parsons Turbine and Generator Conference. All papers have been revised and extended before publication in Materials Science and Technology.

Fatigue life prediction in nickel-based superalloys using unified mechanics theory

“…Advanced nickel-based superalloy RR1000 has been studied for lowcycle fatigue loading conditions. Since RR1000 alloys is a nickel-based superalloy with nickel (gamma phase) as the major component, the base structure is FCC [2][3][4]. RR1000 alloy is used for high-pressure compressor and turbine disks and provides excellent high temperature and fatigue strength [2][3][4].…”

On the Effect of Environmental Exposure on Dwell Fatigue Performance of a Fine-Grained Nickel-Based Superalloy

“…[4] Type I hot corrosion occurs at elevated temperatures (generally > 800°C) and is a result of molten salt deposits, while type II describes the attack of lower melting temperature eutectic salt mixtures that can exist in a stable liquid form around 600°C to 750°C. [5] The increase in operating temperatures of aero-engine components, such as turbine discs, leads to conditions in which type II hot corrosion may be active. It is, therefore, essential to gain a deeper understanding of the mechanism involved and potential prevention routes.…”

“…It is, therefore, essential to gain a deeper understanding of the mechanism involved and potential prevention routes. [5] Previous work on type II hot corrosion of the turbine disc alloy RR1000 was performed by several authors. [5][6][7] Static, stress-free laboratory tests were performed by Encinas-Oropesa et al [7] on RR1000 exposed to SO x gas.…”

“…Oxide spallation was enhanced by the sulfur exposure resulting in material loss and the attack progressed through wide, shallow pit formation. Corrosion-fatigue tests performed by Child et al [5] found that fatigue life can be greatly influenced by altering crack initiation behavior: shorter fatigue lives were obtained by increasing the initial salting level, which increases pitting rates. When sufficient load is applied, linear cracks form from the pits, while under lower loads, corrosion occurs through a mixed-oxide scale formation and spallation.…”

“…When sufficient load is applied, linear cracks form from the pits, while under lower loads, corrosion occurs through a mixed-oxide scale formation and spallation. [5] Cockings et al studied specifically the effect of local salt levels (flux) and stress levels during static or cyclic loading. [6] They performed a systematic study, altering the salt levels and stress levels and found that the hot corrosion response of the alloy could deviate from the simplistic, traditional ''double-bell'' curve, highlighting the requirement for further specific studies characterizing crack tips to elucidate the failure mechanisms.…”