Managing stress: the search for new ‘superalloys’

Managing stress: the search for new ‘superalloys’

Cambridge-Jet-IntroDesigning efficient jet engines is a huge challenge, in part because of the extreme environments inside them, where temperatures can soar above the melting point of the turbine’s components, and the centrifugal forces are equivalent to hanging a double-decker bus from each blade.

This is compounded by demands for greater performance – to run hotter and faster than ever – while improving their efficiency and reducing emissions. This means designing the best possible materials with which to build them.

Enter the Rolls-Royce University Technology Centre (UTC) at the Department of Materials Science and Metallurgy, University of Cambridge.

Founded in 1994, it is one of a global network of over 30 such centres. These form part of Rolls-Royce’s £1 billion annual investment in research and development, which also includes the Department of Engineering’s University Gas Turbine Partnership.

Engineers at the Centre are leading research to develop new superalloys – mixtures of metals capable of withstanding the extreme temperatures and stresses within the jet engine. These materials must combine superior mechanical strength with resistance to heat-induced deformation and corrosion.

Cambridge plays a leading role in a £50 million Strategic Partnership on structural metallic systems for advanced gas turbine applications funded jointly by Rolls-Royce and the Engineering and Physical Sciences Research Council, and involving the Universities of Birmingham, Swansea, Manchester, Oxford, Sheffield, and Imperial College London.

Current jet engines predominantly use nickel based alloys that contain significant amounts of aluminium and up to a dozen other elements. Even the smallest of adjustments to levels of each component can make a significant difference to the structure at a microscopic level, and hence to the superalloy’s properties.

“It’s rather like adjusting the ingredients in a cake – increasing one ingredient might produce one sought-after property, but at the sake of another,” explains Dr Howard Stone, Principal Investigator of the Strategic Partnership. “We need to find the perfect chemical recipe.”

Through a combination of computer modelling and experimental experience, the researchers select components – including both the ‘usual suspects’ and more exotic (though still cost-effective) elements – that can be melted together in precise quantities to produce a prototype material whose mechanical properties can be tested exhaustively.

The team currently has 12 patents with Rolls-Royce, covering a range of new superalloy compositions as well as new materials that may ultimately supersede nickel-based superalloys.

The collaboration between academic and industrial partners has been essential, explains Dr Stone: “New alloys typically take ten years and many millions of pounds to develop for operational components. We simply couldn’t do this work without Rolls-Royce. For the best part of two decades we’ve had a collaboration that links fundamental materials research through to industrial application and commercial exploitation.”

Dr Justin Burrows, Project Manager at Rolls-Royce, agrees: “Our academic partners understand the materials and design challenges we face in the development of gas turbine technology. Improvements like the novel nickel and steel alloys developed in Cambridge are key to helping us meet these challenges and to maintaining our competitive advantage.”

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