2D and 3D characterization of oxidation-fatigue mechanisms in an advanced Ni-based superalloy: Effects of microstructure and elevated temperature

The effects of varying gamma ' size and grain boundary carbide distribution at elevated temperatures on the fatigue behavior of turbine disk alloy RR1000 were examined through combining 2D and 3D imaging characterization. The fatigue crack growth rate at 725 degrees C is higher than at 650 degrees C due to enhanced oxidation damage at higher temperature, dominated by an intergranular fracture mode. This is more marked with longer dwell time (linked to diffusion time) and when carbides have formed continuously at grain boundaries. The fatigue crack path was characterized by X-ray CT scan to present the complex 3D crack propagation morphology. It is noted that a discontinuous crack path and uncracked ligaments can be discerned ahead of the crack tip particularly in the microstructure where carbides are continuously formed at grain boundaries. This is linked to embrittled zones ahead of the crack tip formed during longer dwell times at the maximum stress during cycling at elevated temperature. Effects of microstructure and temperature on fatigue crack growth of Ni-based superalloy. Deeper understanding of high-temperature fatigue mechanism by 2D/3D image characterization. X-ray CT scan revealing complex 3D crack morphology linked to oxidation fatigue mechanism.