Featured Research

from universities, journals, and other organizations

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

Date:
June 5, 2013
Source:
Johns Hopkins University
Summary:
Bubbles in a champagne glass may add a festive fizz, but microscopic bubbles that form in metallic glass can signal serious trouble. That's why researchers used computer simulations to study how these bubbles form and expand.

Still image from an animation of the data from a molecular dynamics simulation of a CuZr metallic glass under hydrostatic loading. Cavitation results, here located near the box edge. Note that the simulation cell is subject to periodic boundary conditions, so only one cavitation event occurs during this simulation. Full video at http://www.youtube.com/watch?v=lpySOUT3gN4
Credit: Michael Falk

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 computer simulations to study how these bubbles form and expand when a piece of metallic glass 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 magnetic properties. 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 Materials Science and Engineering. "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."

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 atoms 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."

The lead author of the Physical Review Letters article was Pengfei Guan, a postdoctoral fellow in Falk's lab. Along with Falk, the co-authors were Shuo Lu, Michael J. B. Spector and Pavan K. Valavala, who were all part of Falk's lab team at the time the research was conducted. The work was supported by National Science Foundation Grant No. DMR0808704.


Story Source:

The above story is based on materials provided by Johns Hopkins University. The original article was written by Phil Sneiderman. Note: Materials may be edited for content and length.


Journal Reference:

  1. Pengfei Guan, Shuo Lu, Michael J. B. Spector, Pavan K. Valavala, Michael L. Falk. Cavitation in Amorphous Solids. Physical Review Letters, 2013; 110 (18) DOI: 10.1103/PhysRevLett.110.185502

Cite This Page:

Johns Hopkins University. "Tiny bubbles in your metallic glass may not be a cause for celebration." ScienceDaily. ScienceDaily, 5 June 2013. <www.sciencedaily.com/releases/2013/06/130605130014.htm>.
Johns Hopkins University. (2013, June 5). Tiny bubbles in your metallic glass may not be a cause for celebration. ScienceDaily. Retrieved October 1, 2014 from www.sciencedaily.com/releases/2013/06/130605130014.htm
Johns Hopkins University. "Tiny bubbles in your metallic glass may not be a cause for celebration." ScienceDaily. www.sciencedaily.com/releases/2013/06/130605130014.htm (accessed October 1, 2014).

Share This



More Matter & Energy News

Wednesday, October 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Argentina's Tax Evaders Detected, Hunted Down by Drones

Argentina's Tax Evaders Detected, Hunted Down by Drones

AFP (Sep. 30, 2014) Argentina doesn't only have Lionel Messi the footballer, it has now also acquired "Mesi" the drone system which monitors undeclared mansions, swimming pools and soy fields to curb tax evasion in the country. Duration: 01:18 Video provided by AFP
Powered by NewsLook.com
Do Video Games Trump Brain Training For Cognitive Boosts?

Do Video Games Trump Brain Training For Cognitive Boosts?

Newsy (Sep. 29, 2014) More and more studies are showing positive benefits to playing video games, but the jury is still out on brain training programs. Video provided by Newsy
Powered by NewsLook.com
CERN Celebrates 60 Years of Science

CERN Celebrates 60 Years of Science

Reuters - Business Video Online (Sep. 29, 2014) CERN, the European Organisation for Nuclear Research, celebrates 60 years of bringing nations together through science. As Joanna Partridge reports from inside the famous science centre it's also planning to turn the Large Hadron Collider particle accelerator back on after an upgrade. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins