Influence of long term aging on microstructure, LCF properties and deformation behaviour of coated nickel-base superalloys at elevated temperatures
(English)Manuscript (preprint) (Other academic)
The objective of this study is to examine and establish the influence of long-term aging on microstructure, low-cycle fatigue life properties and the fracture behaviour of coated polycrystalline and single-crystal nickel-base superalloys. Long-term aging in metallic coating results in the changes of mechanical properties due to the significant interdiffusion of the main alloying elements between substrate and coatings. For this purpose, a polycrystalline nickel-base superalloy IN792 and two single crystal nickel-base superalloys CMSX-4 and SCB coated with three different coatings were used. The coatings were an overlay coating AMDRY997, a platinum-aluminide diffusion coating RT22 and an innovative coating with interdiffusion barrier of NiW called IC1. Cylindrical solid specimens were first aged at 1050oC under 2000 h to simulate long-term exposure of aircraft engine service environment and then cyclically deformed with fully reversed tension-compression loading total strain amplitude control at two elevated temperatures of 500oC and 900oC and a constant strain rate of 10-4s-1 (6%/ min) in air atmosphere without any dwell time. This tests indicate that long-term aging influences the fatigue behaviour and fracture of coated superalloys by oxidation and diffusion mechanisms when compared to non-aged and uncoated samples. Fatigue life of aged samples exhibit longer life in some cases and shorter life during other test conditions. Fatigue cracks in most cases were initiated at the surface of the coating, growing intergranularly perpendicular to the load axis. Major degradation mechanism in AMDRY997 coating deposited on CMSX-4 tested at 900oC is surface oxidation and interdiffusion with the substrate. Cracks in this aged coated system propagated transgranularly through the coating changing the path behaviour when passing the interdiffusion zone.
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-100231OAI: oai:DiVA.org:liu-100231DiVA: diva2:661047