By David Goddard
Metallic glass may sound like an oxymoron, but it’s an actual thing. How is it possible to take the best characteristics of metals and glasses and combine them into one super-strong yet easily malleable material?
Takeshi Egami knows the answer, because he’s been working on it for over 45 years. And there are still plenty of secrets yet to be unlocked.
You may not be familiar with metallic glasses because they’ve been around for only a few generations. But according to Egami, a UT-ORNL Distinguished Scientist and professor of materials science and engineering, it’s only a matter of time until they are everywhere.
“Glasses have existed since the beginning of history, but the science of glasses has always been shrouded by big mysteries,” Egami said. “Due to metallic glass, the newest addition to the glass family, we are now solving those mysteries and will soon be ready to use these materials in technologically advanced products.”
Welcome to the New Age
The key to the metallic glass revolution lies in understanding the properties of both metals and glasses at the atomic level.
Metals offer advantages in strength and durability that are unmatched by other substances. Their conductive properties helped usher in the electronics age. Another positive is the abundance of metals, making them easily available and cost effective.
On the downside, metal atoms tend to line up in an orderly fashion—like a marching band—making the material susceptible to breaking or shearing under heavy loads. Additionally, even the finest metals have a much higher tendency to corrode compared to plastics or glasses.
While regular glasses used in windows clearly don’t have the same inherent strength as metals, the one crucial benefit they offer is that their atoms are arranged chaotically—like a throng of football fans flooding the field after a big victory. This lack of alignment makes straight-line failures nearly impossible.
Their main disadvantage, however, is fragility. Once they start to fail, they fail catastrophically, limiting their use in areas where strength is a concern.
Egami believes that coming up with a material that combines the strength and ductility of metals with the fracture resistance and anticorrosive properties of glass will truly prove to be an important milestone.
“Much like silicon has defined the information age, this new wave of substances will set the tone for coming innovations,” Egami said.
A Cooling-Off Period
The first recorded production of metallic glass happened in 1960. Scientists knew that when a metal melts into a liquid, its atomic structure becomes disorganized. But they discovered that rapidly cooling the molten metal preserves the chaos.
This process produces a glass by locking the atomic structures of the liquid-state metal in place before they can return to solid-state patterns of the crystals.
While that breakthrough proved metallic glass could be fabricated, there were some drawbacks. At the time, only very thin ribbons could be formed because the liquid needed to be cooled so quickly.
As the years progressed, new expertise and alloy development moved the needle exponentially. Today, it’s possible to manufacture metallic glass more than an inch thick—almost a thousand times thicker than the original experiment.
“Our knowledge of the basic properties of liquids and glasses—such as viscosity, strength, and ductility—has increased greatly over time,” Egami said. “We still have a long way to go in understanding the physics, but we are going down the right path. Soon we will be able to design new glasses based upon the science.”
Even though metallic glasses are used in small quantities in many applications, much more research is needed before they can be used in widespread commercial applications. But their properties are promising for a number of reasons.
For example, their tendency to resist scratching and breaking makes metallic glasses ideal for mobile phones, tablets, and laptops. Their strength—even at extremely small widths—could allow them to replace plastics used in those devices.
Other beneficial properties like high strength and low energy loss have made metallic glasses useful in tools and sports equipment such as golf clubs that are designed to convey the maximum possible force.
In an odd twist, the extreme durability of metallic glass could actually hamper its adaptation.
While having a phone that won’t break or a razor that never dulls might seem great for consumers, it could severely limit a company’s profits. Why would they sell something you had to buy only once?
“If they made a product that never broke or never needed replacing, they could sell one to everyone and that would be it,” Egami explained. “There would be no ongoing market.”
So you might say that makes metallic glass a bit of a paradox as well as an oxymoron.
This story is part of the University of Tennessee’s 225th anniversary celebration. Volunteers light the way for others across Tennessee and throughout the world.