Stronger than ceramic yet supple as metals

Strong materials like ceramic are brittle while ductile materials like metals are weak. Researchers at the California Institute of Technology have developed a material that has ceramic-like strength and metal-like ductility. They have achieved this feat through the use of zirconium based metallic glasses and nano-sized pillared structure.

Metallic glass is by no means a new concept, it was first reported in 1960 and has since attracted a lot of attention owing to their superior mechanical properties like high strength and large elastic strain. Amorphous metal, more commonly known as metallic glass, are non-crystalline metallic materials. They are generally produced by rapid cooling of an alloy that has three or more components in it. These alloys achieve their advantages by using atoms of significantly different sizes which results in low free volume, thus higher viscosity. Although they are have poorer electrical and thermal conductivity than metals, the non-crystalline structure avoids crystal defects like grain boundaries and dislocations thus increasing resistance to erosion and corrosion.

Scanning Electron Microscope image of a typical nanopillar

Jang and Greer fabricated nano-sized pillars (see image) from a bulk metallic glass (Zr35Ti30Co6Be29) using an ion beam to etch the material into its final form. They were able to achieve superior strength of 2.25 GPa (which is equivalent to an elephant standing on 1 of that material) and plastic deformability of ~25% by reducing the size to ~500 nm diameter nano pillared structure. At a size reduction to 100 nm, the strength remained same and plasticity was homogeneous. Such high strength has never been reported without sacrificing on the ductility of the material.

With such strength and resistance to erosion, these materials can find application in nanoimprint lithography making nanomolds which are currently silicon-based, expensive and get very easily damaged. Amorphous materials have previously also found use as biomaterials typically as implants in bones. It  is possible to control their rate of dissolution by varying the contents of the alloy and thus become implants which eventually get replaced by bone tissue.

Jang, D., & Greer, J. (2010). Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses Nature Materials DOI: 10.1038/nmat2622

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