Tiny bubbles in your metallic glass may not be a cause for celebration

Jun 05, 2013

Bubbles in a champagne glass may add a festive fizz to the drink, but microscopic bubbles that form in a material called metallic glass can signal serious trouble. In this normally high-strength material, bubbles may indicate that a brittle breakdown is in progress.

That's why Johns Hopkins researchers used to study how these form and expand when a piece of is pulled outward by negative pressure, such as the suction produced by a vacuum. Their findings were published recently in the journal Physical Review Letters.

"A lot of people are interested in metallic glasses because of their strength and their potential use to make better cell phones cases, computer housings and other products," said Michael L. Falk, who supervised the research. "But what precisely causes these materials to break apart or 'fail' has remained a mystery. By studying the behavior of the bubbles that appear when these glasses crack, we were able to learn more about how that process occurs."

When glass is mentioned, many people think of window panes. But to scientists, a glass is a material that is cooled quickly from a liquid to a solid so that its atoms do not arrange themselves into orderly crystal lattices, as most metals do. A nearly random arrangement of atoms gives glasses distinctive mechanical and . Unlike window panes, most metallic glasses are not transparent or easy to break, but they do often spring back to their original shape after being bent. Still, when powerful enough force is applied, they can break.

"Our lab team is interested in learning just how susceptible metallic glasses are to fracturing, how much energy it takes to create a crack," said Falk, a professor in the Whiting School of Engineering's Department of . "We wanted to study the material under conditions that prevail at the tip of the crack, the point at which the crack pulls open the glass. We wanted to see the steps that develop as the material splits at that location. That's where dramatic things happen: atoms are pulled apart; bonds are broken."

This video is not supported by your browser at this time.

At the site where this breakup begins, a vacant space—a bubble—is left behind. The spontaneous formation of tiny bubbles under high negative pressures is a process known as cavitation. The researchers in Falk's lab discovered that cavitation plays a key role in the failure, or breakdown, of metallic glasses.

"We're interested in seeing the birth of one of these bubbles," he said. "Once it appears, it releases energy as it grows bigger, and it may eventually become big enough for us to see it under a microscope. But by the time we could see them, the process through which they had formed would be long over."

Therefore, to study the bubble's birth, Falk's team relied on a computer model of a cube of a metallic glass made of copper and zirconium, measuring only about 30 atoms on each side. By definition, a bubble appears as a cavity in the digital block of metallic glass, with no atoms present within that open space.

"Through our computer model experiments, we wanted to see if we could predict under what conditions these bubbles can form," Falk said.

The simulations revealed that these bubbles emerge in a way that is well-predicted by classical theories, but that the bubble formation also competes with attempts by the glass to reshuffle its to release the stress applied to a particular location. That second process is known as a shear transformation. As the glass responds to pressure, which of the two processes has the upper hand—bubble formation or shear transformation—varies, the researchers found. For example, they determined that bubbles dominate in the presence of high tensile loads, meaning the strong pulling forces that are more common near the tip of a crack. But when the pulling forces were at a low level, the atom reshuffling process prevailed.

Falk and his colleagues hope their findings can help scientists developing new metallic glass alloys for products that can take advantage of the material's high strength and elasticity, along with its tendency not to shrink when it is molded to a particular shape. These characteristics are prized, for example, by makers of cell phones and computers. Producers of such products have expressed interest in metallic glass, and the Falk team's research may help them develop new metallic glass alloys that are less likely to break.

"Our aim is to incorporate our findings into predictive models of failure for these materials," Falk said, "so that they can be optimized and used in applications that require materials that are both strong and fracture-resistant."

Explore further: New research predicts when, how materials will act

Related Stories

Metallic glass: How nanoscale islands react under strain

May 08, 2013

Quick-cooling molten atoms give metal alloys a glassy, or random, atomic structure that generates higher elasticity and better wear- and corrosion-resistance than their crystalline alloy counterparts. However, ...

A new way of making glass

Nov 09, 2012

(Phys.org)—A new way to make glass has been discovered by a collaboration of researchers at the Universities of Düsseldorf and Bristol using a method that controls how the atoms within a substance are ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

Precision gas sensor could fit on a chip

Feb 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

New research signals big future for quantum radar

Feb 26, 2015

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.