A new breakthrough in superspeed pulse mould technology will allow aeroplanes, mobile phone casings and suchlike to be made out of a miraculous type of glass which is as tough as metal, according to the inventors of the new process.
So-called "metallic glass" has been well known since 1960 and has been in industrial production since the 1990s. It is a metal alloy, but one with the disordered structure of glass - not formed into crystals the way most metals are.
The crystalline structure of metal is a disadvantage, making it weak. Unfortunately, ordinary glasses - while strong and rigid - generally crack and shatter easily. What's wanted is a metallic glass, made of metal but with a non-crystalline structure like window glass. This won't crack or fracture, but will be much stronger than an equivalent object made of ordinary metal.
At the moment, metallic glass parts are made by melting and then further heating up metal above 1,000°C which breaks down the crystalline structure. The molten metal is then poured into a steel mould, and cools down in the desired shape to solidify before crystals can form.
The snag with this is that the moulds aren't really strong enough to cope with such temperatures and so they have to be replaced often, which makes metallic-glass objects expensive.
Now, however, a team of boffins has come up with a new plan. Starting with a stick or billet of previously produced solid metalglass with no crystals in it, they would heat it up to a bit more than 500°C. At this stage it becomes liquid enough to be injection moulded in the same fashion as one might injection-mould something out of plastic.
Unfortunately this temperature is not high enough to prevent crystals forming, and they do so in short order. Using any normal means of heating up the metalglass, by the time the whole thing was hot enough to mould it would be crystallised.
Thus the boffins chose not to use any normal method of heating, but rather extremely rapid "ohmic heating". A brief but extremely powerful jolt of electric current is passed through the 2cm metalglass billet, such that for a sub-millisecond period a full megawatt of power is being applied to it.
"We uniformly heat the glass at least a thousand times faster than anyone has before," says William Johnson, engineering prof at Caltech.
Using this method the metalglass is heated up, moulded and cooled to solid again before crystals have any chance to form: the new part is still metalglass, not rubbishy regular metal.
"We end up with inexpensive, high-performance, precision parts made in the same way plastic parts are made—but made of a metal that's 20 times stronger and stiffer than plastic," boasts Johnson.
According to a Caltech statement:
Stronger than steel or titanium — and just as tough — metallic glass is an ideal material for everything from cell-phone cases to aircraft parts.
"We've redefined how you process metals," says Johnson, modestly. "This is a paradigm shift in metallurgy."
The prof and his colleagues have commercialised their process, naturally, and expect to make plenty of cash building the glassy aeroplanes and smartphone cases of tomorrow (hello, iPhone 6?). However, we here on the Reg wonder-materials desk are covering it because the team have published a paper in hefty boffinry mag Science, outlining their work in detail. ®