On the Effect of Environmental Exposure on Dwell Fatigue Performance of a Fine-Grained Nickel-Based Superalloy

Abstract

The influence of sulfur contamination on the corrosion-fatigue behaviour of a polycrystalline superalloy used in aero-engines is considered. Samples tested under a variety of environmental conditions (including exposures to air, SOx gas and salt) are characterised through a suite of high-resolution characterisation methods, including transmission electron microscopy (TEM), secondary ion mass spectroscopy (nanoSIMS) and atom probe tomography (APT). The primary effect of sulfur contamination is to accelerate the crack growth rate by altering the failure mechanism. The SIMS and TEM analyses indicate Cr-Ti sulfide particle formation at grain boundaries ahead and around oxidised cracks. The atom probe tomography analysis suggests that these particles then oxidise as the crack propagates and are enveloped in chromia. The chromia is surrounded by a continuous layer of alumina within the cracks. All of the sulfur detected was confined within the particles, with no elemental segregation found at grain boundaries.