Oxidation of the Ni-based superalloy RR1000 has been undertaken in air over the temperature range 600-900 degrees C for times up to 5000 h. The surface oxide consisted of a protective Ti-doped chromia layer but with rutile forming on its outer surface. Sub-surface oxidation of Al and Ti also occurred. The thickening kinetics of the chromia layer were sub-parabolic with initial rates around two orders of magnitude higher than expected for Ti-free chromia. This enhancement and the sub-parabolic kinetics are accounted for by Ti-doping of the chromia layer. Over time the enhancement reduced because of Ti-depletion in the alloy.

Funding Agencies|Engineering and Physical Sciences Research Council||Rolls-Royce plc||

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Highlights • Two alloy surface treatments are compared. • The kinetics of a Ni-based superalloy are compared to pure chromia formation. • The enhancement is described in terms of Ti-doping of the surface chromia scale. • For the first time, a (Ta,Ti)O 2 phase, formed at the oxide metal interface, is identified.

High temperature oxidation resistance is becoming increasingly important to component life as operating temperatures increase. Additionally, shot-peening is used to help extend the service life of high-duty components through inducing compressive stresses in the surface. The effect of shot-peening on oxidation resistance has not been examined in detail, at least on recent high-strength turbine disc alloys such as RR1000. In this study, oxidation of a coarse-grained variant of RR1000, with and without shot peening, has been characterised over a range of temperatures (700-800 o C) for periods of time extending to 2000 hours. Microstructural characterisation of the oxide and underlying material was performed using a number of techniques. A duplex surface oxide, comprised largely of Cr 2 O 3 covered by a thin top layer of TiO 2 was recorded in both surface conditions. Beneath this surface oxide was an alumina internal oxide, with the shot-peened condition exhibiting more numerous penetrations. The oxide growth kinetics in both alloy conditions were similar.

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