Materials scientists are the alchemists of the 21st century, creating miraculous compounds that appear to achieve the impossible. The aerospace industry is pushing these to their limits, as Neil Glover, chief of materials – capability acquisition at Rolls-Royce, explains.
The heart of a jet engine is like a blast furnace and the hotter it is, the more efficient the engine. So designers face a constant battle to create components that can withstand ever higher temperatures.
Getting the recipe right is critical. Components at the core of the engine, such as turbine blades, are made of nickel-based super alloys that can tolerate very high temperatures and retain their strength even close to their melting point. We add up to a dozen elements to the nickel – chromium for corrosion resistance, aluminium and titanium for strength, tungsten and molybdenum for high temperature performance, and even rhenium (which is very expensive). Each element introduces new compromises, so it’s a delicate balancing act.
Our turbine blades can operate in gas streams up to 200C higher than their melting point. That’s equivalent to keeping an ice cube in an oven without it melting. We achieve this by coating the blades with a microscopic film of insulation material and making them hollow to allow a cooling airflow to pass through them.
We grow each turbine blade as a single crystal for maximum strength. They’re slowly withdrawn from the furnace so the crystal grows up the axis of the blade. The result is 5-10cm long, which is pretty impressive for a single crystal.
Coatings are complex materials systems in their own right. We use an aluminised coating to form a stable oxide and then add a ceramic layer by plasma vapour deposition. This enables us to get the precise structure we want – tiny columns of material that grow outwards from the surface of the metal, resulting in low thermal conductivity and high flexibility as the coating doesn’t crack when the component heats and cools.
It’s a really exciting time to work in materials science. Companies such as Rolls-Royce are under constant pressure to improve engine efficiency by increasing temperatures and reducing weight, and some great new tools and techniques are becoming available. The latest scanning electron microscopes use a focused ion beam that can cut and machine away tiny quantities of material. This enables us to test materials in situ and see exactly what’s going on at a micro-mechanical level.
Now we’re exploring entirely new materials. Nickel alloys are nearing the top of their performance curve. So we’re looking at ceramic matrix composites made of silicon carbides. These are lighter and can tolerate higher temperatures, but they’re not as ductile or damage-tolerant as metal so they pose a fascinating new set of challenges.
Rolls-Royce sponsors a lot of materials science research, including more than 100 PhDs at any one time. In many cases these enthusiastic research scientists are our pipeline of new talent, but we also recruit at graduate level and run undergraduate internships.
Our materials scientists get involved in such a broad range of work, from specification and design to quality control and forensic analysis, that there are many rewarding career paths you can pursue
Read more from original source: http://www.telegraph.co.uk