| Summary: | <p>This thesis provides a research into properties of nickel-based single crystal super- alloys. The underlying quantitative relationship between alloy chemistry and the important properties have been studied. To design new grade of single crystal su- peralloys, computational modelling methods have been proposed which build on the findings of composition-microstructure-property relationships.</p> <p>A physical model for the creep deformation of single crystal superalloys is presented, in which the dependence of the kinetics of creep deformation on alloy chemistry is rationalised. The rate-controlling step is considered to be climb of dislocations at the matrix/particle interfaces and their rate of escape from trapped configurations. The effects of microstructural scale precipitate size, geometry and spacing are also studied. A first order estimate for the rate of creep deformation emerges from the model, which is useful for the purposes of alloy design.</p> <p>Three new single crystal superalloys have been isolated using theory-based com- putational modelling approaches, termed Alloys-By-Design methods. They are (i) an oxidation-resistant low Re-containing alloy with balanced properties, intended for general-purpose gas turbine applications; (ii) an alloy containing 5.6 wt.% Re and 2.6 wt.% Ru suitable for high performance jet engine applications, and (iii) a cheap, corrosion-resistant alloy for power generation applications. The new alloys have been manufactured using investment casting techniques, and their creep and oxidation behaviour evaluated.</p> <p>The multicomponent composition space pertinent to the single crystal nickel-based superalloys has been mapped and searched, by using newly developed numerical al- gorithms. This allowed compositions of alloys conferring the microstructures needed for optimal properties to be identified, at a resolution of 0.1 wt.%. Databases have been constructed which contain all appropriate compositions available in these systems. When coupled with composition- and microstructure-dependent property models, the databases can be searched to identify new alloys predicted to exhibit the very best properties or combinations of them.</p>
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