Effects of creep and oxidation interaction on high temperature crack growth behaviour of nickel based superalloys

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Fisk, Joseph Charles (2013). Effects of creep and oxidation interaction on high temperature crack growth behaviour of nickel based superalloys. University of Birmingham. Ph.D.

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Abstract

A complete and comprehensive understanding of dwell crack growth behaviour is required for two compressor and turbine disc alloys, Udimet 720Li and RR1000, both having a fine grain microstructure. The effect of temperature, dwell time and dwell load has been studied in air and vacuum along with detailed fractographic and microstructural analysis to understand the relevant contributions of oxidation, creep and microstructure. The study has been extended to determine the effect of an overload segment in the load waveform, the rationale being that this type of waveform better models real loading cycles on engines in service. In support with extensive modelling carried out within Rolls-Royce plc in order to understand the stress state ahead of the crack tip and its relaxation over dwell time, the effect of overload factor, test temperature and dwell time has also been examined empirically. In good agreement with the findings of others, crack growth rates according to overload cycling are shown to propagate significantly slower than crack growth rates according to (otherwise similar) dwell-only loading, or static loads; even at high temperature and in an oxidising environment. A good agreement between modelled predictions and experimental results has been achieved, indicating that the retardation of crack growth rates is mainly affected by mechanical factors.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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