Metals. Humans have been developing innovative ways to use these electric-conducive, often shiny, malleable materials for centuries. From creating intricate details in jewelry to forging weaponry and constructing giant structures, the use of metals continues to evolve in modern times.
Even 3D printing has its place on the timeline of metalsmithing, albeit relatively recent. Now, that marker just got bigger in a small way—a very small way. In fact, it is so small that the prints can’t be seen with the naked eye. Thanks to scientists at the California Institute of Technology (Caltech), it’s now possible to create complex nanoscale metal structures using 3D printing.
“Metals don’t respond to light in the same way as the polymer resins that we use to manufacture structures at the nanoscale,” said Greer, professor of materials science, mechanics and medical engineering in Caltech's Division of Engineering and Applied Science. “There's a chemical reaction that gets triggered when light interacts with a polymer that enables it to harden and then form into a particular shape. In a metal, this process is fundamentally impossible.”
That is, until now. In a recent press release, the Caltech team details its study titled “Additive Manufacturing of 3D Nano-architected Metals,” which was recently published in Nature Communications.
The main challenge facing the team was that 3D printing at the nanoscale requires a high-precision laser to zap the liquid using two photons, or particles of light, in specific locations of the material in order to provide enough energy to turn liquid polymers into solids. This process did not create enough energy to fuse metal.
Graduate student Andrey Vyatskikh developed a solution using organic ligands—molecules that bond to metal—to create a polymer resin that carries along with it metal that can be printed. In the experiment, nickel and organic molecules were bonded to create a thick liquid. Still using two photons, the laser created stronger chemical bonds between the organic molecules, hardening them into building blocks and incorporating the nickel into the structure. The team printed a 3D structure initially comprised of metal ions and nonmetal, organic molecules.
The structure then went through a heating process known as pyrolysis. The 3D print was placed into an oven that slowly heated it up to 1,800°F—well below the melting point of nickel, which is 2,650°F—but hot enough to vaporize organic material. The result was a metal structure with dimensions that had shrunk by 80 percent but which maintained its shape and proportions.
“That final shrinkage is a big part of why we’re able to get structures to be so small,” said Vyatskikh, lead author of the paper. “In the structure we built for the paper, the diameter of the metal beams in the printed part is roughly 1/1000th the size of the tip of a sewing needle.”
The team is continuing to perfect its technique. The structure described in the team’s paper includes some voids left behind by the vaporized organic materials as well as some minor impurities. To make its process applicable to various applications, the team plans to expand its process to other metals that are challenging to fabricate into small 3D shapes, including tungsten and titanium. Greer and Vyatskikh also believe this process could be used with other materials, such as ceramics, semiconductors and piezoelectric—materials with electrical effects that result from mechanical stresses.
What does this mean for the metalsmithing timeline? Instead of giant metal bridges, nanoscale “bridges” could be used to create computer chips or ultralight weight metals for things like cars and aircrafts—or even tiny medical implants that could save lives. And, just maybe, a new branch of the timeline will develop that has the potential to create a new class of materials.
For more on nanoscale 3D printing, check out Micro Optics and the World of Nano 3D Printing.