The current demands of the aviation industry for increased gas-turbine efficiency pushes polycrystalline nickel-based superalloy turbine discs to their operational limits. This drive for improved efficiency necessitates higher turbine entry temperatures, requiring that alloys exhibit superior oxidation resistance. The synergistic effects of oxidation and high mechanical stresses pose a complex issue and can be responsible for a reduction in the fatigue life of these components. The principal aim of this thesis is to examine the...