HRL Laboratories Figures Out How to 3D Print Unprintable Metals

Developing a new material for 3D printing isn’t easy – especially metal materials. Creating a new metal powder for 3D printing is a complex and delicate process that requires a great deal of knowledge about material properties, how materials react to certain conditions, and what parameters are necessary for successful printing. There are thousands of different types of metals and alloys out there, and for a long time some of them were thought to be un-3D printable. Almost nothing is truly impossible, though, and a group of engineers at HRL Laboratories have just discovered the secret to 3D printing a couple of particularly tricky aluminum alloys – which opens the door to 3D printing all sorts of previously unprintable metals.

High-strength aluminum alloys such as Al7075 and Al6061 haven’t been well-suited to additive manufacturing in the past because they tend to crack under heat, which also means that they can’t be welded. A 3D printed or welded part made from one of these alloys would simply pull apart. But that’s not the case anymore, thanks to a team led by Hunter Martin and Brennan Yahata, who are both engineers in HRL’s Sensors and Materials Laboratory as well as PhD students in the lab of Professor Tresa Pollock at the University of California, Santa Barbara.

“We’re using a 70-year-old nucleation theory to solve a 100-year-old problem with a 21st century machine,” said Martin.

To solve the problem, the team used a nanoparticle functionalization technique that involved decorating high-strength, “unweldable” aluminum alloy powders with special nanoparticles. The powder is then fed into a 3D printer, but when it melts and solidifies, the nanoparticles act as nucleation sites for the desired alloy microstructure, preventing cracking and enabling the 3D printed part to retain the full strength of the alloy.

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

The method can also be applied to welding, as it operates on the same melting and solidification principle that metal additive manufacturing does. To find the type of nanoparticles with the properties they needed, the team used Citrine Informatics, which led them to zirconium-based nanoparticles.

“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. 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. We went from a haystack to a handful of possible needles.”

This work represents a breakthrough – not only can it be used to 3D print and weld high-strength aluminum alloys, which are in high demand for aerospace and automotive applications, it can also be applied to other difficult materials such as high-strength steels and nickel-based superalloys. This could open the door to wider use of additive manufacturing in fields like aerospace, which has already adopted the technology on a widespread basis but has been limited by the difficulty in 3D printing certain metals.

The research was documented in a paper entitled “3D printing of high strength aluminum alloys,” which you can access here. Authors include John H. Martin, Brennan D. Yahata, Jacob M. Hundley, Justin A. Mayer, Tobias A. Schaedler and Tresa M. Pollock.

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[Source/Images: HRL Laboratories]