Fatigue crack growth of UDIMET 720 Li superalloy at elevated temperature

The fatigue crack growth rate and fracture behaviour of a nickel-base super alloy UDIMET 720 Li was investigated at 700 degreesC in vacuum and air envi ronments using corner crack specimens. The effects of load ratio at a frequ ency of 0.25 Hz were examined while the effects of loading frequency from 5 Hz to 0.008 Hz were also examined for a constant load ratio. The mode of f racture was intergranular at all load ratios at a frequency of 0.25 Hz in a n air environment. Two-parameter models were proposed to describe separatel y the effects of load ratio and frequency. The model prediction was combine d with data from vacuum tests to form a fracture mechanism map showing limi ted contribution of creep, while oxidation controls the fatigue crack growt h rate as the frequency decreases. (C) 2001 Elsevier Science Ltd. All right s reserved.