Fatigue crack growth of UDIMET 720 Li superalloy at elevated temperature

The fatigue crack growth rate and fracture behaviour of a nickel–base superalloy UDIMET 720 Li was investigated at 700°C in vacuum and air environments using corner crack specimens. The effects of load ratio at a frequency 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 fracture was intergranular at all load ratios at a frequency of 0.25 Hz in an air environment. Two-parameter models were proposed to describe separately the effects of load ratio and frequency. The model prediction was combined with data from vacuum tests to form a fracture mechanism map showing limited contribution of creep, while oxidation controls the fatigue crack growth rate as the frequency decreases.