Increasing one ingredient might produce one sought-after property, but at the sake of another – we need to find the perfect chemical recipe.
- Howard Stone
Inside a jet engine is one of the most extreme environments known to engineering.
In less than a second, a tonne of air is sucked into the engine, squeezed to a fraction of its normal volume and then passed across hundreds of blades rotating at speeds of up to 10,000 rpm; reaching the combustor, the air is mixed with kerosene and ignited; the resulting gases are about a third as hot as the sun’s surface and hurtle at speeds of almost 1,500 km per hour towards a wall of turbines, where each blade generates power equivalent to the thrust of a Formula One racing car.
Turbine blades made from ‘super’ materials with outstanding properties are needed to withstand these unimaginably challenging conditions – where the temperatures soar to above the melting point of the turbine components and the centrifugal forces are equivalent to hanging a double-decker bus from each blade.
Even with these qualities, the blades require a ceramic layer and an air cooling system to prevent them from melting when the engine reaches its top temperatures. But with ever-increasing demands for greater performance and reduced emissions, the aerospace industry needs engines to run even hotter and faster, and this means expecting more and more from the materials they are made from.
This, says Dr Cathie Rae, is the materials grand challenge. “Turbine blades are made using nickel-based superalloys, which are capable of withstanding the phenomenal stresses and temperatures they need to operate under within the jet engine. But we are running close to their critical limits.”
An alloy is a mixture of metals, such as you might find in steel or brass. A superalloy, however, is a mixture that imparts superior mechanical strength and resistance to heat-induced deformation and corrosion.
Rae is one of a team of scientists in the Rolls-Royce University Technology Centre (UTC) at the Department of Materials Science and Metallurgy. The team’s research efforts are focused on extracting the greatest possible performance from nickel-based superalloys, and on designing superalloys of the future.
Current jet engines predominantly use alloys containing nickel and aluminium, which form a strong cuboidal lattice. Within and around this brick-like structure are up to eight other components that form a ‘mortar’. Together, the components give the material its superior qualities.
“Even tiny adjustments in the amount of each component can have a huge effect on the microscopic structure, and this can cause radical changes in the superalloy’s properties,” explains Dr Howard Stone. “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. We need to find the perfect chemical recipe.”
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Image: Rotor
Credit: Rolls-Royce Plc
Reproduced courtesy of the University of Cambridge
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