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Title: Characterisation of the microstructural evolution of single crystal nickel-base superalloys
Author: Cox, D. C.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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The work contained in this thesis is devoted to the study of microstructural evolution of nickel-based superalloy single crystals. The main issues addressed, are improved understanding of the mechanisms of microstructural evolution with regard to; (i) processing variables; (ii) the effect of in-service conditions. The majority of the work concentrates on the second-generation single crystal nickel-base superalloy CMSX-4. Data is gathered and analysed from a series of experiments studying different aspects of microstructural evolution. Throughout the work extensive use is made of metallographic and microscopical techniques. The first experimental part of this work (Chapter 3) investigates the solidification behaviour and elemental microsegregation contained in single crystal castings. Dendrite arm spacing, microsegregation and solidification range are studied and compared in three different single crystal superalloys, SRR99, CMSX-4 and RR3000. Chapter 4 studies the sensitivity of a nickel-base superalloy, CMSX-4, to recrystallisation. This phenomenon occurs as a result of castings undergoing plastic strain in the mold during solidification and cooling. The subsequent homogenisation heat-treatment that cast single crystals must undergo in order to reduce dendritic microsegregation then results in the casting recrystallising. This work establishes critical strain and temperature values necessary for recrystallisation to occur following the introduction of plastic strain at both room and elevated temperature. Chapter 5 studies the effects of age heat-treatment on the creep rupture behaviour of CMSX-4 at three different stress and temperature regimes. Different γ\γ', microstructures have been developed via modified age heat-treatments, and it is the effects of these modifications on the creep rupture behaviour that are investigated. The study uses mainly scanning electron microscopy to investigate the effects and evolution of the microstructure during the creep tests, and the creep behaviour is rationalised in terms of the developed microstructures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available