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Title: Solidification characteristics, microstructural stability and creep behaviour of advanced ruthenium-bearing nickel-base single crystal superalloys
Author: Hobbs, Robert Anthony
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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The principal objective of this thesis is to identify the mechanism(s) by which Ru retards topologically close-packed (TCP) precipitation and to assess its influence on single crystal solidification and intermediate to high temperature creep, with the aim of improving the casting yield of next generation single crystal turbine blades whilst maintaining creep resistance and long term microstructural stability. The effect of Ru on single crystal solidification was found to be negligible, suggesting its concentration may be adjusted to levels necessary to improve other properties, such as microstructural stability, without great determent to the solidification characteristics of the alloy. Ru was confirmed to be a potent microstructural stabilising element with respect to TCP precipitation. The effect appears predominantly thermodynamic in nature due to a combination of γ’ destabilisation and an affinity between Re and Ru atoms decreasing the enthalpy of mixing in the γ phase which effectively increases the solubility limits of Re in the matrix. The marked decrease in TCP nucleation rate seems to be a secondary effect of this reduced driving force for TCP precipitation. Ru enhanced the creep rupture properties throughout the intermediate to high temperature creep regimes. Its potency as a solid solution strengthener decreased with rising temperature whereas its effectiveness as a stabilising element increased with temperature. It is postulated that the reduction in γ’ volume fraction upon the addition of Ru, which is central to its effectiveness as a stabilising element, is the principal cause of its diminishing strengthening contribution at elevated temperatures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available