An experimental and computational study of damage and crack growth for a nickel-based superalloy under fatigue-oxidation conditions

Oxidation damage, in conjunction with fatigue, is a concern for nickel-based superalloys utilised as disc rotors in high pressure compressor and turbine of aero-engines. A combined experimental and numerical study has been carried out for alloy RR1000, developed at Rolls- Royce plc through a powder metallurgy route to meet the demands for higher overall pressure ratios, compressor discharge temperatures and rotational speeds for the latest aero-engines. Cyclic experiments have been carried out for waisted specimens at selected temperatures (700°C-800°C), followed by microscopy examination using Focused Ion Beam (FIB). The results suggest that the major mechanism of oxidation damage consists of the formation of surface oxide scales and internal micro-voids and oxide particles beneath the oxide scales, which becomes more severe with the increase of temperature. Applying a cyclic stress does not change the nature of oxidation damage but tends to enhance the extent of oxidation damage for temperatures at 750°C and 800°(, Further energy dispersive X-ray (EDX) analyses show the enrichment of Cr and Ti, together with lower Ni and Co levels, in the surface oxide scales, suggesting the formation of brittle Cr203, Ti02, NiO and C030 4 oxides on the specimen surface. Penetration of oxygen into the material and associated internal oxidation, which leads to further material embrittlement and associated failure, are evidenced from both secondary ion imaging and EDX analyses.EThOS - Electronic Theses Online ServiceGBUnited Kingdo