When is a crystal not a crystal? When it’s a quasi-crystal, a paradoxical form of metal recently found in some 3D printed metal alloys by [A.D. Iams et al] at the American National Institute for Standards and Technology (NIST).

As you might remember from chemistry class, crystals are made up of blocks of atoms (usually called ‘unit cells’) that fit together in perfect repetition — baring dislocations, cracks, impurities, or anything else that might throw off a theoretically perfect crystal structure. There are only so many ways to tessellate atoms in 3D space; 230 of them, to be precise. A quasicrystal isn’t any of them. Rather than repeat endlessly in 3D space, a quasicrystal never repeats perfectly, like a 3D dimensional Penrose tile. The discovery of quasicrystals dates back to the 1980s, and was awarded a noble prize in 2011.
Penrose tiling– the pattern never repeats perfectly. Quasicrystals do this in 3D. (Image by Inductiveload, Public Domain)
Quasicrystals aren’t exactly common in nature, so how does 3D printing come into this? Well, it turns out that, quite accidentally, a particular Aluminum-Zirconium alloy was forming small zones of quasicrystals (the black spots in the image above) when used in powder bed fusion printing. Other high strength-alloys tended to be very prone to cracking, to the point of usability, and this Al-Zr alloy, discovered in 2017, was the first of its class.

You might imagine that the non-regular structure of a quasicrystal wouldn’t propagate cracks as easily as a regular crystal structure, and you would be right! The NIST researchers obviously wanted to investigate why the printable alloy had the properties it does. When their crystallographic analysis showed not only five-fold, but also three-fold and two-fold rotational symmetry when examined from different angles, the researchers realized they had a quasicrystal on their hands. The unit cell is in the form of a 20-sided icosahedron, providing the penrose-style tiling that keeps the alloy from cracking.

You might say the original team that developed the alloy rolled a nat-20 on their crafting skill. Now that we understand why it works, this research opens up the doors for other metallic quasi-crystals to be developed on purpose, in aluminum and perhaps other alloys.

We’ve written about 3D metal printers before, and highlighted a DIY-able plastic SLS kit, but the high-power powder-bed systems needed for aluminum aren’t often found in makerspaces. If you’re building one or know someone who is, be sure to let us know.

hackaday.com/2025/04/18/d20-sh…

This fun PCB from [Nick Brown] features a miniature railroad implemented with 0805-sized LEDs. With an eye towards designing his own fun interactive PCB badge, the Light-Rail began its journey. He thoroughly documented his process, from shunting various late-night ideas together to tracking down discrepancies between the documentation of a part and the received part.

Inspired by our very own Supercon 2022 badge, he wanted to make a fun badge with a heavy focus on the aesthetics of the final design. He also wanted to challenge himself some in this project, so even though there are over 100 LEDs, they are not laid out in a symmetrical or matrix pattern. Instead, it’s an organic, winding railroad with crossings and stations throughout the board. Designed in KiCad the board contains 144 LEDS, 3 seven-segment displays, and over a dozen buttons that all come together in use for the built in game.

The challenges didn’t stop at just the organic layout of all those LEDs. He decided to use Rust for this project, which entailed writing his own driver for the seven-segment displays as well as creating a tone library for the onboard buzzer. As with all projects, unexpected challenges popped up along the way. One issue with how the oscillator was hooked up meant he wasn’t able to use the ATmega32U4, which was the brains of the entire railroad. After some experimenting, he came up with a clever hack: using a pogo pin jig to connect the clock where it needed to go while programming the board.

Be sure to check out all the details of this journey in his build log. If you love interactive badges also check out some of the other creative boards we’ve featured.

hackaday.com/2025/04/18/track-…