Editor's Note: This article originally appeared in the June 2025 print edition of Aerospace Manufacturing and Design under the headline “Quasicrystal defects make aluminum alloy stronger.”
Andrew Iams was examining a sliver of a new aluminum alloy at the atomic scale, searching for the key to its strength, when he noticed the atoms were arranged in an extremely unusual pattern. “That’s when I started to get excited,” says Iams, a materials research engineer at the National Institute of Standards and Technology (NIST), “because I thought I might be looking at a quasicrystal.”
Crystals and quasicrystals
A traditional crystal is any solid made of atoms or molecules in repeating patterns. Table salt is a common crystal whose atoms connect to make cubes, and those microscopic cubes connect to form bigger cubes large enough to see with the naked eye. Quasicrystals’ unique shape lets them form a pattern that fills the space but never repeats.
In metals, perfect crystals are weak. The regular patterns of perfect crystals make it easier for the atoms to slip past each other. When that happens, the metal bends, stretches, or breaks.
Quasicrystals enhance metal 3D printing
When used in metal powder bed fusion 3D printing, high-strength aluminum alloys tend to develop cracks, making them unusable. A commercially available high-strength aluminum alloy for 3D printing adds zirconium to the aluminum powder to prevent 3D-printed parts from cracking, resulting in a strong alloy. Iams and the NIST team wanted to know what made this alloy formed under the extreme conditions of metal 3D printing so strong. They found part of the answer was quasicrystals, which break up the regular pattern of aluminum crystals, and these defects make the metal stronger.
Identifying quasicrystals
When Iams looked at the crystals, he saw they had fivefold rotational symmetry, meaning there are five ways to rotate the crystal around an axis so it looks the same.
“Fivefold symmetry is very rare. That was the telltale sign that we might have a quasicrystal,” Iams says. To confirm a quasicrystal, Iams had to rotate the crystal under the microscope and show that it also had threefold symmetry and twofold symmetry from two different angles.
“We’ve shown quasicrystals can make aluminum stronger. Now people might try to create them intentionally in future alloys,” says NIST physicist Fan Zhang.
Understanding this aluminum on the atomic scale could enable a whole new category of 3D-printed parts using quasicrystals for strength in airplane components and heat exchangers.
National Institute of Standards and Technology (NIST)
https://www.nist.gov
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