When is a crystal not just a crystal? The answer lies in the intriguing world of quasi-crystals, a fascinating form of metal recently uncovered in some 3D printed metal alloys by researchers from the American National Institute for Standards and Technology (NIST), including A.D. Iams and his team.

If you recall your chemistry lessons, you might remember that crystals are composed of blocks of atoms, commonly referred to as unit cells. These unit cells fit together in a precise, repetitive mannerprovided there are no dislocations, cracks, impurities, or other imperfections disrupting this theoretically flawless structure. In total, there are precisely 230 unique ways to tessellate atoms in three-dimensional space. However, a quasicrystal deviates from this norm; instead of repeating uniformly, a quasicrystal manifests a non-repetitive structure, reminiscent of a Penrose tile in three dimensions. The groundbreaking discovery of quasicrystals dates back to the 1980s, culminating in a Nobel Prize award in 2011 for this pivotal advancement in materials science.

Quasicrystals are not commonly found in nature, leading to the question: how does 3D printing relate to this extraordinary phenomenon? Interestingly, it has been discovered that a specific Aluminum-Zirconium alloy forms small zones of quasicrystalsillustrated as black spots in an accompanying imagewhen processed using powder bed fusion printing techniques. This extraordinary alloy, identified in 2017, was the first of its kind and emerged as a solution to a significant problem faced by engineers: many high-strength alloys were prone to cracking to such an extent that they became unusable.

One might predict that the irregular structure of a quasicrystal would distribute stresses differently, reducing the likelihood of crack propagation compared to a regular crystal structure. This hypothesis turned out to be correct! The researchers at NIST embarked on an investigation to understand the underlying reasons for the remarkable properties of this printable alloy. Their crystallographic analysis revealed not only five-fold rotational symmetry but also three-fold and two-fold symmetries when the sample was examined from various angles. This realization confirmed the presence of a quasicrystal within the alloy, characterized by a unique unit cell in the shape of a 20-sided icosahedron, which provides the Penrose-style tiling that enhances the alloy's resistance to cracking.

It's almost as if the original team responsible for developing this alloy achieved a remarkable stroke of luck in craftinga natural 20 on their crafting skill, if you will! With a clearer understanding of why this material behaves the way it does, this groundbreaking research paves the way for the intentional development of other metallic quasicrystals, not just in aluminum but potentially in a variety of alloys.

We've previously covered the fascinating realm of 3D metal printers and even highlighted do-it-yourself plastic SLS kits; however, the high-powered powder-bed systems necessary for aluminum printing are still quite rare and not typically found in average makerspaces. If you or someone you know is working on building one of these advanced systems, we would love to hear about it!