Abstract
The low cycle fatigue (LCF) behaviour of four variants of UDIMET®720 was investigated. The materials comprised a fine grained (approximately 10 μm), powder processed material with a fine bimodal distribution (∼20 and 80 nm) of secondaryγ′; the same material, but with enlarged secondaryγ′ (∼480 nm); a coarse grained powder processed material (grain size ∼62 μm) and finally a cast and wrought material with a similar microstructural scale to the fine grained powder processed alloy, but with reduced interstitial element content. LCF testing was undertaken on corner notched square section specimens at 20, 300 and 600 °C with a frequency of 0.25 Hz, a cyclic stress range of 500 MPa and anRratio of +0.1. At 20 and 600 °C fracture was found to be macroscopically flat for all materials. However, at 300 °C, significant shear fracture was observed in the two materials that had a fine grain size and a fine secondaryγ′ size, leading to a characteristic ‘tear‐drop’ appearance. Only minor shear fracture was observed in the coarse grained and enlarged secondaryγ′ materials. Tensile tests indicated that weak dynamic strain ageing occurred in all materials at 300 °C. The fine grained powder processed U720 also exhibited dynamic strain ageing at 600 °C, but this was not the case for the coarse grained or cast and wrought materials. The origin of the shear fracture are discussed and related to the microstructure.
Published Version
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