At the end of last year, researchers at the California Institute of Technology announced the successful development of a new manufacturing technology for printing micro metal parts, which are only three to four sheets of paper thick. Now, the team has once again innovated this technology, which can print objects as small as 150 nanometers in size, comparable to the size of influenza viruses. During this process, the team also found that the atomic arrangement inside these small objects was in a disordered state. Contrary to traditional cognition, this atomic level disorder actually improved the quality of these materials, making their strength potentially three to five times higher than similar sized structures with more ordered atomic arrangements.
On November 6, 2023, this study was conducted in the laboratory of Professor Julia R. Greer, an expert in materials science, mechanics, and medical engineering at the California Institute of Technology and director of the Fletcher Jones Foundation's Cavelli Institute for Nanoscience. Detailed information on this discovery has been published in a paper in the journal Nano Express.
The title of the paper is "Suppressing the Size Effect of Nanocolumns with Layered Microstructure through Nanoscale Additive Manufacturing" (Transport Gate)
This new technology is similar to another technology announced by the team last year, but each step has been redesigned to adapt to the nanoscale. However, this also brings an additional challenge: the created objects are so small that they are invisible to the naked eye and difficult to manipulate.
Nanoscale lattice prepared using new technology developed by Julia R. Greer's laboratory
Next, the hydrogel is partially injected into an aqueous solution containing nickel ions. Once these components are saturated with metal ions, they will be baked until all the hydrogels are burned out. The remaining parts have the same shape as the original ones, although they have shrunk and are completely composed of metal ions that are now oxidized, combined with oxygen atoms. In the final step, oxygen atoms are chemically peeled off from the part, converting the metal oxide back into metallic form.
rregular internal structure of △ nanoscale nickel columns
Unusual microstructure
Greer stated: In this process, all these thermal and dynamic processes occur simultaneously, resulting in a very, very chaotic microstructure. You will see defects such as pores and irregularities in the atomic structure, which are usually considered factors for strength deterioration. If you want to build something with steel, such as an engine cylinder block, you will not want to see this type of microstructure because it significantly weakens the strength of the material
However, Greer said their findings were exactly the opposite. Many defects can weaken metal components on a larger scale, but for nanoscale components, they can have a strengthening effect.
When there are no defects in the pillars, catastrophic failures occur at the so-called grain boundaries (where the microscopic crystals that make up the material collide with each other).
But when the material is filled with defects, it is difficult for failure to propagate from one grain boundary to the next. This means that the material will not suddenly fail, as deformation is more evenly distributed throughout the entire material.
Mechanical engineering graduate student Zhang Wenxin works in the nanomanufacturing laboratory
3D printing has entered the nano field
The main author of the study Zhang Wenxin, a graduate student in mechanical engineering, explained: Normally, deformed carriers, such as dislocations or slippage, in metal nanopillars propagate until they can escape from the outer surface. However, in the presence of internal pores, propagation will quickly terminate on the pore surface rather than continue throughout the entire pillar. Based on experience, nucleating the deformed carrier is more difficult than making it propagate, which explains why the current pillar may be stronger than its corresponding pillar
Greer believes that this is one of the first demonstrations of 3D printing of nanoscale metal structures. She pointed out that this process can be used to manufacture many useful components, such as hydrogen catalysts; Carbon free storage electrodes for ammonia and other chemicals; And important components of equipment such as sensors, micro robots, and heat exchangers.
She said, "We were very worried at first. We thought, oh my god, this microstructure will never bring any benefits. But obviously, we have no reason to worry because it turns out to be not even a form of damage. It is actually a function
Overall, this process requires multiple complex steps and specific processes to prepare nanoscale materials, which is a highly specialized task that cannot be achieved on regular 3D printers at present, but has enormous potential for the future.
