Characterisation and behaviour of advanced Ni-based superalloys at elevated temperatures

Increasing the operating temperature of gas turbines improves their efficiency, which is essential for economic and environmental reasons. This requires new or improved materials; however the behaviour of these at elevated temperatures must be understood to avoid catastrophic in-service failure. This project focuses on the crack growth behaviour of two powder metallurgy Ni-based superalloys, used in Rolls-Royce gas turbine discs. One alloy is currently in revenue service (RR1000); the other alloy is expected to enter service in the coming years (RR1073). Dwell fatigue tests (where the sample is held at maximum load for a specified time) will be performed to establish crack growth mechanisms in RR1073. Crack growth retardation at low Delta K values and behaviour at crack thresholds will be compared for both alloys. The effect of test piece geometry on crack growth rate and retardation will be explored, and digital image correlation (DIC) and finite element analysis (FEA) will be used to understand and model behaviour at the crack tip for both alloys. This work will contribute towards lifing of the new disc alloy, so that failure in service may be avoided.