Bringing the bounce: Unusual chemical structure gives new metallic glass material its elasticity

Glass isn’t only a versatile material; it’s crucial to our everyday modern lives.

It makes our roads safer, it’s vital to the development of new green energy solutions, it helps repair human bodies, and the material is fast-approaching nearly indestructible strength status.

Glass also is a stellar partner when it comes to joining forces with other materials.

Glass and ceramic pull together for better batteries.

Scientists at Kansas State University (Manhattan, Kan.) are exploring new glassy ceramic material combinations and electrode designs that will afford lithium-ion batteries with high capacity, efficiency, and stability as well as high mass loading.

Glass and metal pair up for ultra-powered windows.

Researchers at the University of British Columbia (Canada) recently found that coating small pieces of glass with very thin layers of metal makes it possible to enhance the amount of light coming through the glass. And because metals naturally conduct electricity, this power pairing may make it possible to add advanced technologies to windowpanes and other glass objects.

Glass and graphene create robust electronic material.

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory, Stony Brook University, and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute developed a simple and powerful method for creating resilient, customized, and high-performing graphene: layering it on top of soda-lime glass.

Most recently, engineers at the University of Southern California, University of California, San Diego, and the California Institute of Technology (Pasadena, Calif.) created a new metallic glass material with an unusual chemical structure that makes it incredibly hard and yet elastic, according to a USC News article.

The material, called SAM2X5-630, can withstand heavy impacts without deformation, the article explains. And it retains most of its original strength when pushed beyond its elastic limits without fracturing.

SAM2X5-630 falls into the category of “bulk metallic glasses” or BMGs, a class of artificially generated materials that possess disproportionate strength, resilience, and elasticity due to their unusual chemical structure, according to the article.

“Typical metals and metal alloys have an organized, crystalline structure at the atomic level. BMGs are formed when metal and metal alloys are subjected to extreme heat and then rapidly cooled, exciting their atoms into disorganized arrangements and then freezing them there,” the article explains.

To create SAM2X5-630, the team heats powdered iron composite to 630 degrees Centigrade (1166 degrees Fahrenheit) and then rapidly cools it. The team uses a spark plasma sintering process in which the iron compound is powdered, placed in a graphite mold, and zapped with a current under pressure, the article explains. The technique superheats the powdered iron enough to bind it without liquefying it.

Spark plasma sintering saves time and money. “You can produce materials that normally take hours in an industrial setting in just a few minutes,” Olivia Graeve, ACerS member and professor of mechanical engineering at the Jacobs School of Engineering at UC San Diego, says in a UC San Diego news release. Graeve led design and fabrication work on the material.

But what makes SAM2X5-630 particularly interesting is that it’s not wholly a glass. The team found that controlling the exact amount of heat and timing to create the material is the key to its unique properties. If the same iron composite is heated and cooled at even slightly different temperatures or paces, it results in a totally different atomic structure that doesn’t deliver on the same elastic properties.

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Transmission electron microscopy image showing different levels of crystallinity embedded in the amorphous matrix of the alloy. Credit: UC San Diego

According to the UC San Diego news release, a 1.5–1.8 mm-thick piece of SAM2X5-630 has a Hugoniot Elastic Limit of 11.76 ± 1.26 GPa. “By comparison, stainless steel has an elastic limit of 0.2 GPa, while that of tungsten carbide (a high-strength ceramic used in military armor) is 4.5 GPa.”

(Check out a video from USC that shows a BMG ball bouncing in action.)

“It [SAM2X5-630] has almost no internal structure, like glass, but you see tiny regions of crystallization,” Veronica Eliasson, assistant professor at the USC Viterbi School of Engineering and lead author of the research, says in the article. “We have no idea why a small amount of crystalline regions in these bulk metallic glasses makes such a big difference under shock loading.”

The unique qualities of SAM2X5-630 make the material widely applicable for use in protective shields like body armor for soldiers and meteor-resistant casings for satellites.

“The fact that the new material performed so well under shock loading was very encouraging and should lead to plenty of future research opportunities,” Eliasson adds.

The open-access paper, published in Scientific Reports, is “Shock wave response of iron-based in situ metallic glass matrix composites,” (DOI:10.1038/srep22568).


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