Weigh ahead

UK researchers plan to develop a lightweight nanostructured aluminium alloy that is up to 10 times stronger than existing equivalents and can operate at much higher temperatures.

The work of the Oxford University team will build on recent advances in nanotechnology, which have opened the way for a nanostructured class of cast metal matrix composites (MMCs).

Cheaper, lighter and stronger than traditional alloys, MMCs have a wide variety of applications.

The versatile materials have been used since the 1960s to create more energy-efficient car engines that run on low oil, lead-free plumbing fixtures, and tanks that are light enough to be airlifted but as tough as heavier varieties.

The team is preparing to study a new stronger version of these MMCs that will be both lightweight and highly resilient. Funded by a three-year, £900,000 EPSRC grant, researchers hope the work will lead to the development and widespread use of a next-generation alloy that can withstand temp- eratures up to 400ºC. Most commercial aluminium alloys lose their useful strengths at temperatures above 250ºC.

The university will work with project partners including Rolls-Royce and automotive technology specialist Prodrive.

Now a significant industry in its own right, MMCs have been used in components for car brakes, jet landing gear and even the Hubble Space Telescope. The higher strength-density ratio of these materials has been of intense interest over the years due to the energy saved by reduced mass.

MMCs are fabricated by combining metal with a completely different class of material, such as ceramics and recycled waste. Incorporating the two materials — the matrix and the reinforcement materials — results in remarkable structural and physical properties not seen in the natural world.

Over the course of the research programme, the team will develop nanostructured MMCs and demonstrate their routes for bulk manufacture by testing engineering components in real-world applications. The team will study two different categories of nanostructured aluminium alloys: bulk nanoquasicrystalline alloys and nanofibril metal-metal composites.

In the final year, the researchers will choose an alloy composition and production process to develop prototype components such as pistons, inlet valves, compressor blades and plates.

The project's principal researcher, Prof George Smith of the department of materials, said he was unable to give further details as he was awaiting patent approvals, but claimed there was a lot of excitement about the possible results.

'The project really is cutting edge and it is absolutely red hot as far as the industrial collaborators are concerned,' he said.

But others with knowledge of the subject offered some informed opinion. Prof Leon Shaw of the University of Connecticut, has studied the effects of stress on nanocrystalline multi-phase aluminum alloys. His research showed that the alloy lost ductility when temperatures rose above 300ºC. However, the key to making these, or any other type of alloy, stronger, Shaw suggests, is using smaller particles.

'With conventional alloys, the particle grain is normally micron-sized,' he said. 'Nanomaterial means the grain will be nanosize — 1,000 times smaller. Once you go down to that level the strength will get higher.'

Smaller particles create denser materials that are less likely to dislocate and deform. 'So once the dislocation cannot move, the material becomes stronger,' he said. 'And once you go down to really fine particles, dislocation could totally disappear depending on how fine a grain is. If it's below 10 nm, deformation mode completely changes.'

Shaw said the cost of manufacturing these nanostructured materials could be similar to the cost of manufacturing conventional alloys. However, he said that even if they are more expensive to produce,there would still be an incentive to buy them.

'My personal view is that the first application for these alloys will be racing cars,' he said, 'because they don't really care about the price. All they want is to win the competition, and if these materials provide higher performance and let them win races, they'll pay off a lot.'

Shaw said he also saw applications in the military, aerospace and automotive sectors.