Abstract
The effects of cyclic-frequency, hold-time, and stress-intensity factor on rates of fatigue crack growth in air at 500-700°C have been studied for Waspaloy - a nickel-based superalloy used for gas turbine engine discs. At 700°C, the two main effects were: (i) smaller crack-growth increments per cycle at longer hold times (> 2 s) at low AK, and (ii) larger crack-growth increments per cycle at lower cyclic frequencies at high δK, compared with those at a base-line cyclic frequency of 2 Hz. Similar, but lesser, effects were observed at 600 and 500°C. The results are discussed in terms of the competing effects of enhancement of cracking due to creep and slip-localisation, and inhibition of cracking due to decreases in the effective AK caused by fracture-surface-roughness induced crack closure, oxide-induced crack-closure, and crack branching.
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