The cylinder shown here is an amorphous iron alloy, or metallic glass, made using an additive manufacturing technique. Photo credit: Zaynab Mahbooba.
Scientists have developed a new method to produce amorphous metal or metallic glass alloys in bulk, which could be used in a number of industries.
A research team from North Carolina State University has demonstrated the ability to the alloys with a 3D printer, which have a bevy of applications including for electric motors that are more efficient, better wear-resistant materials, higher strength materials and lighter weight structures.
“Metallic glasses lack the crystalline structures of most metals – the amorphous structure results in exceptionally desirable properties,” Zaynab Mahbooba, the first author of a paper on the work and a PhD student in North Carolina State University’s Department of Materials Science and Engineering, said in a statement.
Making metallic glass requires rapid cooling so the crystalline structure cannot form, forcing researchers to only cast metallic glasses into small thicknesses. For example, amorphous iron alloys could be cast no more than a few millimeters thick. The size limitation is called an alloy’s critical casting thickness.
“The idea of using additive manufacturing, or 3D printing, to produce metallic glass on scales larger than the critical casting thickness has been around for more than a decade,” Mahbooba said. “But this is the first published work demonstrating that we can actually do it. We were able to produce an amorphous iron alloy on a scale 15 times larger than its critical casting thickness.”
The researchers applied a laser to a layer of metallic powder, melting it into a solid layer—about 20 microns thick. The build platform then descends 20 microns and more powder is spread onto the surface, with the process repeating itself.
Because the alloy is formed a little at a time, it cools quickly and retains its amorphous qualities, but is still a solid, metallic glass object.
“This is a proof-of-concept demonstrating that we can do this,” Ola Harrysson, a corresponding author of the paper and Edward P. Fitts Distinguished Professor of Industrial Systems and Engineering at NC State, said in a statement. “And there is no reason this technique could not be used to produce any amorphous alloy. One of the limiting factors at this point is going to be producing or obtaining metal powders of whatever alloy composition you are looking for. For example, we know that some metallic glasses have demonstrated enormous potential for use in electric motors, reducing waste heat and converting more power from electromagnetic fields into electricity.”
Mahbooba said it would take some trial and error to find the best combination of properties from the alloys for each specific application.
“For instance, you want to make sure you not only have the desirable electromagnetic properties, but that the alloy isn’t too brittle for practical use,” Mahbooba said.
The study was published in Applied Materials Today.
