Sep 21, 2017 | By Benedict

HRL Laboratories, a Boeing-owned corporate R&D lab located in Malibu, California, has developed a technique for successfully 3D printing high-strength aluminum alloys, including Al7075 and Al6061. The technique could have big implications for aerospace and automotive.

As more and more researchers look to get involved with additive manufacturing research, more materials are becoming 3D printable—wood, ceramics, and even food are some of the more unusual substances to be turned printable in the name of additive manufacturing progress.

From an economic perspective, however, few of those breakthroughs will prove to be as significant as HRL Laboratories’ recent discovery: a technique for printing previously unprintable aluminum alloys.

Capable of processing high-strength alloys like Al7075 and Al6061 (as well as certain steels and nickel-based superalloys), this new technique could be an absolute game-changer for the aerospace and automotive industries, potentially providing a way to fabricate important components for new planes, cars, and other systems.

Strangely enough, the secret to the breakthrough can be traced back to the middle of the 20th century.

“We're using a 70-year-old nucleation theory to solve a 100-year-old problem with a 21st century machine,” commented HRL’s Hunter Martin, who co-led the team alongside Brennan Yahata, a fellow engineer in the HRL Sensors and Materials Laboratory and PhD student at the University of California.

The duo have authored a research paper on the study, titled “3D printing of high-strength aluminum alloys,” under the supervision of Professor Tresa Pollock, who was also a co-author. It was published in the journal Nature.

So what’s different about this new metal 3D printing technique that borrows from bygone theories? Well, most crucially, it uses a process called “nanoparticle functionalization” to “decorate” high-strength (but unweldable) alloy powders with specially selected nanoparticles.

The powders, newly adorned with these nanoparticles, are fed into a 3D printer, which layers the powder and fuses each layer in the normal manner of Selective Laser Melting (SLM).

The difference is that during the melting and solidification process, the specially added nanoparticles act as “nucleation sites” for the desired alloy microstructure. And the effect of this is absolutely massive.

Try printing alloys like Al7075 and Al6061 on a normal SLM 3D printer and the metal will eventually suffer hot cracking, with the printed part able to be pulled apart like a bit of pastry. Not very useful for engineering applications.

But the nucleation sites prevent this hot cracking, allowing for retention of full alloy strength in the 3D printed part. The consequence? Printable high-strength alloys that could be used to make the next generation of aircraft and automobiles.

The nanoparticle functionalization process could have other consequences too. For example, it could be used to make unweldable alloys weldable, since melting and solidification in additive manufacturing is basically a small-scale, precise version of welding.

The technique is also scalable and employs low-cost materials.

“Our first goal was figuring out how to eliminate the hot cracking altogether,” Martin explained. “We sought to control microstructure and the solution should be something that naturally happens with the way this material solidifies.”

Of course, one of the most important steps was identifying the right nanoparticles. In this case, those were zirconium-based nanoparticles, assessed and identified with the aid of Citrine Informatics, an advanced materials and chemicals platform.

“Using informatics was key,” said Yahata. “The way metallurgy used to be done was by farming the periodic table for alloying elements and testing mostly with trial and error. The point of using informatics software was to do a selective approach to the nucleation theory we knew to find the materials with the exact properties we needed.”

And by cooperating closely with the Citrine Informatics team, the HRL researchers were able to find the solution to their nanoparticle problems much faster than they could have on their own.

“Once we told them what to look for, their big data analysis narrowed the field of available materials from hundreds of thousands to a select few,” Yahata said. “We went from a haystack to a handful of possible needles.”

Excitingly, the HRL team even thinks the new technique could benefit additive manufacturing processes besides SLM. They say the method “provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting.”

The research paper, whose other authors were Jacob Hundley, Justin Mayer, and Tobias A. Schaedler, can be read here.



Posted in 3D Printing Technology



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