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Nickel-base superalloys are used in the hottest part of jet engines and power plant, in particular for the turbine blades that extract energy from the gas stream. These alloys are used at up to 80% of their melting point, a feat unreproduced in any other material system, and last for thousands of hours of service in a harsh, high load, oxidising environment. However, further improvements in fuel efficiency, resulting in cost improvements, reduced greenhouse-gas, NOW and SO2 emissions and reductions in weight, require that the operating temperature of these blades continues to increase. This requires that the creep of these alloys be predicted based on the microstructure of the alloys, in particular the evolution of the dislocation distribution, misfit between the Y-Ni3Al phase and the Ni matrix, the size distribution of the 'y' and the composition of each phase, since in these alloys are composed of up to 14 different alloying elements.Historically, creep, or time-dependent strain, in these materials has been predicted using empirical equations that are fitted to test data. At Imperial College, we have been developing a model that accounts explicitly for the microstructural features of these alloys, in particular the evolution of the dislocation distribution, since creep is the product of the generation, glide and entrapment of dislocations, which are line defects. However, we have not linked our models with models of microstructure before, instead treating the composition, distribution, misfit and volume fractions of the phases as fixed input data. In this proposal, we propose to link our model directly to enhanced versions of recently-developed precipitation models of these microstructural features, and then incorporate the entire model set into the finite element codes used by gas turbine manufacturers to design engines.Of course, data about the behaviour of these materials is tightly held by the engine manufacturers, because it is a key source of their competitive advantage over each other and because the design assumptions they use inform the design and service of their products. For this program, we are partnering with the only two UK gas turbine manufacturers, Siemens-Westinghouse (Industrial gas turbines in Loncoln, UK) and Rolls-Royce (Aero engines in Derby, UK), who are each leaders in their sectors. They have agreed to provide us with design data of the service conditions and both new and service-exposed blades in order for us to validate our models against the actual behaviour observed in service. In addition, so as to examine clearly some of the more unusual features of the creep behaviour under tightly-controlled conditions, we will perform creep tests using both the virgin and service-exposed material. This combination of laboratory testing and actual component examination is extremely unusual in a scientific creep research program. Both the companies and the UK MOD as one of the biggest UK users of gas turbines are interested in using the models we produce to enhance their design and service-interval calculations, which will reduce their costs and enhance their competitive position.The research will also train both a PhD student and a postdoctoral researcher in creep and microstructure modelling and in advanced electron microscopy techniques, enabling them to move to the forefront of this critical field. Our past graduates of similar programs find wide employment with gas turbine manufacturers, research labs and universities both in the UK, EU and around the world. The research will be presented at leading international conferences, ensuring that it is used by the wider superalloys community.
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