Engineers in the US have created a new, incredibly hard, incredibly elastic metallic glass. For those unaware, metallic glass is, in general, already incredibly hard and incredibly elastic.
Engineers have developed a new type of metallic glass called SAM2X5-630 that can withstand very heavy impacts without deforming, even when it’s impressive elastic limits are breached.
Bulk metallic glass (BMG) is essentially unstructured metal, which is created by taking typical metals – which are in an orderly, periodic, ‘crystalline’ structure at the atomic level –and melting them down into a liquid.
This liquid metal loses all structure, before it is then cooled down very quickly, freezing in the structureless, ‘amorphous’ atomic construction. Similar to how glass is made, thus the name.
When two objects collide, their crystalline structure forces together into a tight ‘fit’, before bouncing away. It is this forcing process that absorbs the kinetic energy. The structureless glass, though, acts differently, making it far more bouncy – so things like drills or golf clubs, which want the entire force to be on the object they hit, are suitors for metallic glass.
What the people behind this current discovery did, though, is cool down the melted liquid marginally slower than usual, meaning tiny areas of structure managed to form in parts of SAM2X5-630.
“It has almost no internal structure, like glass, but you see tiny regions of crystallisation,” said Veronica Eliasson, lead author of the paper and assistant professor at the USC Viterbi School of Engineering. “We have no idea why a small amount of crystalline regions in these bulk metallic glasses makes such a big difference under shock loading.”
And that shock loading is significant. Current forms of BMGs are twice as strong as titanium. SAM2X5-630, though, enjoys a Hugoniot Elastic Limit of 11.76 ± 1.26 GPa (the size of the BMG was 1.5-1.8mm thick).
For reference, stainless steel has an elastic limit of 0.2 GPa, while that of tungsten carbide (a high-strength ceramic used in military armor) is 4.5 GPa. At the top end, diamonds are 60 GPa.
Here’s a nice explainer on BMGs in general.
Main metal image via Shutterstock