Metal with extra mettle

US researchers have developed a form of non-magnetic steel that can be processed like plastic and is three times stronger than conventional steel.

Formulated at the University of Virginia, the material represents the latest breakthrough in the development of amorphous metals – materials with a non-crystalline or ‘glassy’ structure rather than the ordered crystalline structure of conventional metals. Unaffected by the crystallographic defects that can affect other metals, such materials are up to three times stronger and more corrosion resistant than conventional metals.

Prof William Johnson of the California Institute of Technology (and founder of Liquidmetal, the company that owns the licence to University of Virginia’s amorphous metal technologies), explained that the Darpa-funded project represents the first step towards harnessing the enviable properties of amorphous steel for larger structural applications.

Amorphous materials are typically made by cooling liquid metal fast enough to avoid crystallisation and efforts to improve them are largely focused on devising materials that do this more easily.

Johnson explained that while engineers have been looking at amorphous alloys since the 1960s, the Virginia team’s alloy exhibits an unprecedented resistance to crystallisation. So it is potentially far easier and less expensive to produce and can be cast into sheets 1cm thick, making it ideal for a broad range of applications.

Project leader Prof Joseph Poon, who claimed the material will revolutionise the steel industry, said that it could be used to make ship hulls, lighter cars and even surgical instruments.

Johnson added that the potentially high costs will be offset by the ease with which the metal can be processed. He explained that it will soon be possible to make complex metal parts from amorphous metals using techniques similar to those employed in the plastics processing industry.

Thus complex shapes, stronger than components that would usually be machined or die-cast, could be produced using a process similar to plastic injection moulding.

He explained that while steel is typically cast at 1,600 degrees C, Virginia’s amorphous alloys could be formed at around 550 degrees.

‘Look around you at how metal is used in precision parts and imagine plastically moulding these parts at a relatively low temperature.’ He added that it could even be possible to blow-mould the metal: ‘With a sheet of this material you could blow-mould a car fender twice as strong as an ordinary fender.’

In the shorter term the first applications for the material are likely to be in the military arena. Its high strength and low density, coupled with its non-magnetic properties, make it particularly attractive for use in the hulls of submarines – where not only would it improve the structural strength of the boat but also help it avoid detection by removing its magnetic signature.

Another military application is in the development of armour-piercing projectiles, where rounds made from amorphous steel are effectively sharpened as they penetrate their target. Johnson said that prototypes of these ‘self-sharpening penetrators’ are being trialled by the US military as a possible alternative to depleted uranium ordnance.

While the project is still at the research stage and producing the material in relatively small quantities, Poon claimed that it will be ready for wider industrial application within three years. The material still requires some tweaking to make it less brittle and an economic and efficient production method must be developed.

Johnson suggested that the three-year prediction may be a little over-optimistic, but was no less enthusiastic about the potential of the technology.

‘Knowing the properties of this material and the potential for processing it like plastic it’s almost certain that within a decade it will replace conventional metal technology,’ he said.