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Materials

3-D printers make aluminum pieces without cracks

Nanoparticles help print metal alloys more effectively

by Bethany Halford
September 21, 2017 | APPEARED IN VOLUME 95, ISSUE 38

Credit: Bryan Ferguson
An aluminum alloy powder mixed with nanoparticles is ready for 3-D printing.

Three-dimensional printing has become a popular method for making objects with complex geometries. But use of metal alloys with the technique, which could produce components for aerospace and automotive applications, has lagged. Of the 5,500 alloys in industrial use today, only about 10 can be printed. That’s because metal alloys are typically 3-D printed by rastering a laser across a bed of metal alloy powder to fuse it layer-by-layer. But the way these alloys crystallize as they cool usually results in many little cracks, and therefore poor mechanical properties, in the printed part.

By adding just 1% of zirconium hydride nanoparticles to high-strength aluminum alloy powder, researchers at HRL Laboratories and the University of California, Santa Barbara, managed to eliminate these small cracks, creating superior 3-D printed aluminum alloys (Nature 2017, DOI: 10.1038/nature23894). The technique could potentially be used on many different alloys, dramatically expanding the number of metals that are compatible with the manufacturing process.

“Our approach was to change the way these materials solidify,” explains J. Hunter Martin, who led the research team. The nanoparticles have just the right geometry to act as seed crystals throughout the molten alloy, providing a multitude of tiny nucleation sites for the alloy to crystallize around.

“The approach used here is an elegant and simple way to enable 3-D printing of aluminum alloys, which are important for many applications but have been difficult to print until now,” comments Michael Dickey, an expert in liquid metal alloys at North Carolina State University.

Martin says that the nanoparticles don’t increase the materials costs by a substantial margin and that they’re easy to incorporate into the alloy powders using HRL’s proprietary process. His team is currently working on scaling up the process to 3-D print hundreds of kilograms of metal alloys at a time.

Even so, Martin says, there are many hurdles to overcome before the technique is used commercially simply because the process and the materials are new. Once widely adopted, however, 3-D printed alloys could dramatically change how metal parts are made, Martin notes. “The vision is that you’d have full geometric freedom to design any component you want.”

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