Apr 16, 2014
Blow forming makes BMGs the easy way
A new and speedy way to identify ideal bulk metallic glass alloys has been put forward by researchers at Yale University in the US. The new technique, which relies on so-called parallel blow forming, could do away with the need for the sequential and time-consuming trial-and-error approaches that are usually employed to develop these materials. The team has already used its technique to identify a good magnesium-copper-yttrium glass alloy that can be made by thermoplastic moulding.
The new method is a versatile toolbox that quickly and easily unveils complex combinations of bulk metallic glasses (BMGs), says team leader Jan Schroers, and it should help researchers increase the rate at which they discover new and potentially useful compositions of these materials. BMGs are technologically important alloys that are stronger than steels, but that can be processed like thermoplastics. They are used in applications such as electronic casings, sporting goods like golf clubs and tennis handles, and in watches. They have also found their way into solar-light collectors, resonators and military materials that are stronger, lighter and more effective at high stress than conventional bulletproof composites.
BMGs were only discovered quite recently and they can contain more than 30 elements that include transition metals, near metalloids, rare earths and alkali metals. The best combinations are usually found by sequential trial-and-error techniques that search for properties like a material’s thermoplastic formability (TPF). A BMG’s TPF is defined by how easily it can be processed in its unique supercooled liquid state and depends on how long the material takes to crystallize and its viscosity. However, the problem is that calculating crystallization times and viscosities is no easy task.
Simpler to measure the maximum strain a BMG can withstand
Schroers’ team says that the maximum strain a BMG can withstand before it crystallizes under certain predefined conditions (for example, during blow forming) is a much simpler parameter to measure. What is more, such a parameter is a direct measure of a BMG’s TPF.
The researchers developed a high-throughput strategy to identify BMG alloys with maximum TPFs among thousands of possible combinations. “We employed a blow forming technique,” Schroers told nanotechweb.org. “The further we can blow a bubble from the BMG, the better the alloy. But instead of doing this for each composition individually, we fabricated thousands of membranes of different alloys and positioned gas-releasing agents underneath these membranes. The gases blow up the membranes and we simply measure the strain produced by this expansion.”
Finding alloys 1000 times faster
According to the researchers, the technique allows them to identify a good BMG alloy 1000 times faster than is possible using conventional methods. “It will also allow us to combine desired features in the alloy, such as mechanical properties and its plastic forming ability, as well as cost and environmental aspects,” said Schroers. “In some cases, we might even be able to control specific characteristics like a BMG’s colour and electrochemical activity.”
The Yale team says that it is now busy developing various metallic glasses using its method – and especially trying to fabricate those alloys that have proved prohibitively difficult to make in the past, like systems based on aluminium or tungsten.
The current work is detailed in Nature Materials doi:10.1038/nmat3939
About the author
Belle Dumé is contributing editor at nanotechweb.org