Scientists forge "superhard" metals using new nanoparticle manufacturing processes

2024-01-04

Researchers at Brown University have developed a new method for manufacturing "superhard" metals. The team created nanoparticle "building blocks" that can fuse together under moderate pressure through chemical treatment. The hardness of a material specifically describes its ability to resist deformation within the local volume on its surface. In the case of metals, it is usually determined by the size of the microscopic grains that make up it - the smaller the grains, the harder the metal.

Usually, the hardness of metals is achieved through macroscopic manufacturing methods such as hammering, bending, or twisting. But in the new research, the research team started from a "bottom-up" perspective, which greatly improved the hardness of the metal.

"Hammering and other quenching methods are methods that change the grain structure from top to bottom, making it difficult to control the final grain size," said Ou Chen, the corresponding author of the study. "What we do is create nanoparticle components, and when you squeeze them, they merge together. This way, we can have uniform grain sizes that can be precisely adjusted to enhance performance."

The team stated that the problem is that the surface of metals is often covered by organic molecules called ligands, which prevent strong binding of metal particles. Researchers have developed a chemical treatment method that can remove these ligands, allowing metal nanoparticles to freely blend together through pressure sintering processes.

Using this method, researchers made rough "coins" from nanoparticles of different metals such as gold, silver, and palladium. In the test, they were proven to have significantly increased hardness compared to usual, with the gold coins having a hardness four times higher than before. The other physical properties remain largely unchanged.

In another test, researchers used their new technology to create a type of metallic glass. Like glass, which we are familiar with, these materials have an amorphous crystal structure, which makes them easier to shape and may be stronger than ordinary metals.

"Making metallic glass with a single component is notoriously difficult, so most metallic glasses are alloys," the researchers said. "But we can start with amorphous palladium nanoparticles and use our technology to manufacture palladium metallic glasses."

Researchers suggest that at the current centimeter scale, this process can be used to manufacture superhard coatings, electrodes, or other metal components. But according to the team, it should also be relatively simple to expand to larger projects, as current industrial equipment can handle the pressure of use.

The study was published in the journal Chem.

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