Engineers achieve longstanding goal of stable nanocrystalline metals
By By David L. Chandler, MIT News Office | 25 Aug 2012
Most metals - from the steel used to build bridges and skyscrapers to the copper and gold used to form wires in microchips - are made of crystals: orderly arrays of molecules forming a perfectly repeating pattern. In many cases, including the examples above, the material is made of tiny crystals packed closely together, rather than one large crystal.
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| Tongjai Chookajorn, left, and Heather Murdoch, the lead authors of Science paper on the design and production of new stable nanocrystalline metal alloys with exceptional strength and other properties. Photo: Dominick Reuter |
Indeed, for many purposes, making the crystals as small as possible provides significant advantages in performance, but such materials are often unstable: the crystals tend to merge and grow larger if subjected to heat or stress.
Now, MIT researchers have found a way to avoid that problem. They've designed and made alloys that form extremely tiny grains - called nanocrystals - that are only a few billionths of a meter across. These alloys retain their nanocrystalline structure even in the face of high heat. Such materials hold great promise for high-strength structural materials, among other potential uses.
The new findings, including both a theoretical basis for identifying specific alloys that can form nanocrystalline structures and details on the actual fabrication and testing of one such material, are described in a paper published Aug. 24 in Science.
Graduate student Tongjai Chookajorn, of MIT's department of materials science and engineering (DMSE), guided the effort to design and synthesise a new class of tungsten alloys with stable nanocrystalline structures.
Her fellow DMSE graduate student, Heather Murdoch, came up with the theoretical method for finding suitable combinations of metals and the proportions of each that would yield stable alloys. Chookajorn then successfully synthesised the material and demonstrated that it does, in fact, have the stability and properties that Murdoch's theory predicted.
