Researchers create amorphous metallic glass alloys using 3D printing
A laser melts the powder into a solid layer that is only 20 microns thick. The alloy is formed a little at a time, it cools quickly, allowing it to retain amorphous qualities.0
Researchers at North Carolina State University are using 3D printing to create amorphous metal, or metallic glass, alloys.
In order to make metallic glass, the material requires rapid cooling to prevent the crystalline structure from forming. For the most part, researchers have cast these metallic glasses into small gauges. For example, amorphous iron alloys could be cast no more than a few millimeters thick. That size limitation is called an alloy’s critical casting thickness.
This is where 3D printing comes into the picture.
“The idea of using additive manufacturing to produce metallic glass on scales larger than the critical casting thickness has been around for more than a decade,” Mahbooba says. “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.”
A laser is applied to a layer of metal powder, melting the powder into a solid layer that is only 20 microns thick. The “build platform” then descends 20 microns, more powder is spread onto the surface, and the process repeats itself. Because the alloy is formed a little at a time, it cools quickly, allowing it to retain amorphous qualities. The end result is a solid, metallic glass object, not an object made of laminated, discrete layers of the alloy.
These alloys will offer properties that will make them suitable for a variety of different applications such as more efficient electric motors, better wear-resistant materials, higher strength materials, and lighter weight structures.
“And there is no reason this technique could not be used to produce any amorphous alloy,” says Ola Harrysson, corresponding author of the paper and Edward P. Fitts Distinguished Professor of Industrial Systems and Engineering at NC State.
“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.”
“It will take some trial and error to find the alloy compositions that have the best combination of properties for any given application,” says Zaynab Mahbooba, first author of a paper on the work and a Ph.D. student in North Carolina State University’s Department of Materials Science and Engineering. “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.”
Harrysson adds that using additive manufacturing allows the team to produce these metallic glasses in a variety of complex geometries.