“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]