Researchers use 3-D printing to create metallic glass alloys in bulk

March 22, 2018 by Matt Shipman, North Carolina State University
The cylinder shown here is an amorphous iron alloy, or metallic glass, made using an additive manufacturing technique. Credit: Zaynab Mahbooba

Researchers have now demonstrated the ability to create amorphous metal, or metallic glass, alloys using three-dimensional (3-D) printing technology, opening the door to a variety of applications – such as more efficient electric motors, 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," 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.

Unfortunately, making metallic glass requires rapid cooling to prevent the crystalline structure from forming. Historically, that meant researchers could only cast into small thicknesses. For example, amorphous iron could be cast no more than a few millimeters thick. That size limitation is called an alloy's critical casting thickness.

"The idea of using , or 3-D printing, 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."

The technique works by applying a laser 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 – retaining its amorphous qualities. However, the end result is a solid, metallic glass object – not an object made of laminated, discrete layers of the alloy.

"This is a proof-of-concept demonstrating that we can do this," says Ola Harrysson, corresponding author of the paper and Edward P. Fitts Distinguished Professor of Industrial Systems and Engineering at NC State.

"And there is no reason this technique could not be used to produce any amorphous alloy," Harrysson says. "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," Mahbooba says. "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."

"And because we're talking about additive manufacturing, we can produce these metallic glasses in a variety of complex geometries – which may also contribute to their usefulness in various applications," Harrysson says.

The paper, "Additive manufacturing of an iron-based bulk metallic larger than the critical casting thickness," is published in the journal Applied Materials Today.

Explore further: Magnetic materials increase energy density in power transformation

More information: Zaynab Mahbooba et al. Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness, Applied Materials Today (2018). DOI: 10.1016/j.apmt.2018.02.011

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dnatwork
5 / 5 (1) Mar 22, 2018
If you throw in copper and some insulating material (maybe a metal oxide?), you could build the whole electric motor in the 3D printer. Change the heating/cooling regime for areas in the iron that you want to have harder or whatever (where you need support more than conduction), and you pop the finished product straight on to your Tesla (or whatever).

Maybe scale this down very small, mix in some diamond, make nanomotors.
Parsec
not rated yet Mar 23, 2018
If you throw in copper and some insulating material (maybe a metal oxide?), you could build the whole electric motor in the 3D printer. Change the heating/cooling regime for areas in the iron that you want to have harder or whatever (where you need support more than conduction), and you pop the finished product straight on to your Tesla (or whatever).

Maybe scale this down very small, mix in some diamond, make nanomotors.


I suspect that the best idea is to construct each piece that requires different materials separately if at all possible. Evry extra type of material multiplies the complexity of the rig a lot.
Eikka
not rated yet Mar 23, 2018
If you throw in copper and some insulating material (maybe a metal oxide?)


The limitations are that you have to spread the material uniformly over the object as powder, and the fact that oxides have high melting points and/or they get reduced to the base metal when heated.

Differing material composition along the printed object run into the problem of the powders mixing together, forming different alloys than what was intended.
mackita
1 / 5 (2) Mar 23, 2018
The usage of metallic glass has no big advantage in 3D printing IMO. The resulting material is porous and it absorbs deforms - which is just the stuff, which the metal glass alloys were developed against. It's like making a soft plasticine from diamond dust.
Eikka
not rated yet Mar 24, 2018
The usage of metallic glass has no big advantage in 3D printing IMO


Metallic glass has many advantages even if it's porous. In fact, being porous allows for a trick that helps agains the main downside of metallic glass: the glass shatters at its elastic limits becuse the cracks grow instantly through the whole material; not so with a porous structure where the cracks stop at the pores and the whole part doesn't fall apart catastrophically.

and it absorbs deforms - which is just the stuff, which the metal glass alloys were developed against.


What does "absorbs deforms" mean?

Metallic glass has high intrinsic resistance to eddy currents, so it's useful in transformers and motors. and they're springier than regular alloys so they can deform better without losing their original shape.

mackita
1 / 5 (1) Mar 24, 2018
Metallic glass has high intrinsic resistance to eddy currents, so it's useful in transformers and motors. and they're springier
These properties will just get negligible in form of porous 3D printed metal foam.
Eikka
5 / 5 (1) Mar 24, 2018
Metallic glass has high intrinsic resistance to eddy currents, so it's useful in transformers and motors. and they're springier
These properties will just get negligible in form of porous 3D printed metal foam.


No they don't. The pores simply increase the mean path lenght for the eddy currents, making it resist the formation of current loops even more. That leads to higher efficiency in magnetic circuits, like motor core laminations.

Like, why magnetic cores are often made of sintered materials in the first place. Only, you can't make a sintered motor core because it would be weak, but now you can thanks to metallic glass.
Thorium Boy
1 / 5 (1) Mar 25, 2018
There are no real metallic glasses. Glass that was mixed at the molecular level with metal would be something fascinating.
24volts
not rated yet Mar 26, 2018
I wonder if they could make a type that would be very magnetic at one end and like MU metal at the other end. That could be really useful.

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