Creep behaviour of single crystal nickel base superalloy

The creep activation energy and structure constant at the different creep stages have been calculated, and the microstructures have been observed by SEM and TEM. The results showed that the internal stress sigma(o) decreased with an increase in temperature. Over the stress and temperature range, there are different activation energies, time exponents, and structure constants at different creep stages. The change in microstructure has an influence on creep resistance in this superalloy (Ni-6.0Al-7.0Ta-8.5Mo, wt-%). It is shown that the dislocation climb is the major deformation mechanism during tensile creep stages I and II, but during the tertiary stage, the creep resistance decreased as a result of dislocations shearing into the gamma' rafts. Creep fracture occurs mainly by the cavities and microcracks produced at the gamma'/gamma phase interface due to the interaction of multislips.