Rare crystal shape increases strength of 3D printed aluminum
NIST researchers found that non-repeating quasicrystals create defects that strengthen the metal
According to the National Institute of Standards and Technology (NIST), researchers have found special atomic patterns called quasicrystals in 3D printed aluminum alloys. When Andrew Iams, a materials research engineer, was examining a sliver of a new aluminum alloy through his electron microscope, he noticed atoms arranged in an unexpected pattern. “That’s when I started to get excited because I thought I might be looking at a quasicrystal.” He and colleagues at NIST confirmed the presence of quasicrystals and found they strengthened the aluminum alloy. Their findings were published in the Journal of Alloys and Compounds.
The alloy formed under the extreme conditions of metal 3D printing. This discovery may lead to new aluminum alloys specifically designed to leverage quasicrystals for improved strength.
Quasicrystals differ from regular crystals, which have repeating atomic patterns, like salt crystals forming cubes. Quasicrystals fill space without ever repeating their patterns. Dan Shechtman discovered quasicrystals at NIST in the 1980s, a discovery initially doubted but later validated, earning him a Nobel Prize in 2011. Decades later, working in the same facility, Iams found quasicrystals in 3D printed aluminum.
Aluminum has been notoriously difficult to 3D print. “High-strength aluminum alloys are almost impossible to print,” said Fan Zhang, a physicist at NIST. “They tend to develop cracks, which make them unusable.” Aluminum typically melts around 700°C but needs to be heated far beyond its boiling point (2,470°C) when used to 3D print – altering its properties.
In 2017, researchers from HRL Laboratories and UC Santa Barbara created a zirconium-enhanced aluminum alloy that could be printed without cracking. NIST examined this aluminum-zirconium alloy to understand its atomic structure. “In order to trust this new metal enough to use in critical components such as military aircraft parts, we need a deep understanding of how the atoms fit together,” said Zhang. They found quasicrystals played a critical role.
In metals, perfect crystals weaken the structure by allowing atoms to slip easily, causing deformation. Quasicrystals interrupt this regular pattern, creating defects that strengthen the metal. “Now that we have this finding, I think it will open up a new approach to alloy design,” said Zhang.
