Subscribe free to our newsletters via your
. 24/7 Space News .




TECH SPACE
Making strong, tough metallic glass cheaply
by Marcus Woo
Pasadena CA (SPX) May 16, 2011


Metallic glasses, which were first discovered at Caltech in 1960 and later produced in bulk form by Johnson's group in the early 1990s, are not transparent like window glass. Rather, they are metals with the disordered atomic structure of glass.

Stronger than steel or titanium - and just as tough - metallic glass is an ideal material for everything from cell-phone cases to aircraft parts. Now, researchers at the California Institute of Technology (Caltech) have developed a new technique that allows them to make metallic-glass parts utilizing the same inexpensive processes used to produce plastic parts.

With this new method, they can heat a piece of metallic glass at a rate of a million degrees per second and then mold it into any shape in just a few milliseconds.

"We've redefined how you process metals," says William Johnson, the Ruben F. and Donna Mettler Professor of Engineering and Applied Science. "This is a paradigm shift in metallurgy." Johnson leads a team of researchers who are publishing their findings in the May 13 issue of the journal Science.

"We've taken the economics of plastic manufacturing and applied it to a metal with superior engineering properties," he says. "We end up with inexpensive, high-performance, precision net-shape parts made in the same way plastic parts are made-but made of a metal that's 20 times stronger and stiffer than plastic." A net-shape part is a part that has acquired its final shape.

Metallic glasses, which were first discovered at Caltech in 1960 and later produced in bulk form by Johnson's group in the early 1990s, are not transparent like window glass. Rather, they are metals with the disordered atomic structure of glass. While common glasses are generally strong, hard, and resistant to permanent deformation, they tend to easily crack or shatter. Metals tend to be tough materials that resist cracking and brittle fracture-but they have limited strength. Metallic glasses, Johnson says, have an exceptional combination of both the strength associated with glass and the toughness of metals.

To make useful parts from a metallic glass, you need to heat the material until it reaches its glass-transition phase, at about 500? degrees C. The material softens and becomes a thick liquid that can be molded and shaped. In this liquid state, the atoms tend to spontaneously arrange themselves to form crystals. Solid glass is formed when the molten material refreezes into place before its atoms have had enough time to form crystals. By avoiding crystallization, the material keeps its amorphous structure, which is what makes it strong.

Common window glass and certain plastics take from minutes to hours-or longer-to crystallize in this molten state, providing ample time for them to be molded, shaped, cooled, and solidified. Metallic glasses, however, crystallize almost immediately once they are heated to the thick-liquid state. Avoiding this rapid crystallization is the main challenge in making metallic-glass parts.

Previously, metallic-glass parts were produced by heating the metal alloy above the melting point of the crystalline phase-typically over 1,000 degrees C. Then, the molten metal is cast into a steel mold, where it cools before crystallizing. But problems arise because the steel molds are usually designed to withstand temperatures of only around 600 degrees C. As a result, the molds have to be frequently replaced, making the process rather expensive. Furthermore, at 1,000 degrees C, the liquid is so fluid that it tends to splash and break up, creating parts with flow defects.

If the solid metallic glass is heated to about 500? degrees C, it reaches the same fluidity that liquid plastic needs to have when it's processed. But it takes time for heat to spread through a metallic glass, and by the time the material reaches the proper temperature throughout, it has already crystallized.

So the researchers tried a new strategy: to heat and process the metallic glass extremely quickly. Johnson's team discovered that, if they were fast enough, they could heat the metallic glass to a liquid state that's fluid enough to be injected into a mold and allowed to freeze-all before it could crystallize.

To heat the material uniformly and rapidly, they used a technique called ohmic heating. The researchers fired a short and intense pulse of electrical current to deliver an energy surpassing 1,000 joules in about 1 millisecond-about one megawatt of power-to heat a small rod of the metallic glass.

The current pulse heats the entire rod-which was 4 millimeters in diameter and 2 centimeters long-at a rate of a million degrees per second. "We uniformly heat the glass at least a thousand times faster than anyone has before," Johnson says. Taking only about half a millisecond to reach the right temperature, the now-softened glass could be injected into a mold and cooled-all in milliseconds.

To demonstrate the new method, the researchers heated a metallic-glass rod to about 550 degrees C and then shaped it into a toroid in less than 40 milliseconds. Despite being formed in open air, the molded toroid is free of flow defects and oxidation.

In addition, this process allows researchers to study these materials in their molten states, which was never before possible. For example, by heating the material before it can crystallize, researchers can examine the crystallization process itself on millisecond time scales. The new technique, called rapid discharge forming, has been patented and is being developed for commercialization, Johnson says.

In 2010, he and his colleagues started a company, Glassimetal Technology, to commercialize novel metallic-glass alloys using this kind of plastic-forming technology.

The other authors on the Science paper, "Beating crystallization in glass-forming metals by millisecond heating and processing," are Caltech's Georg Kaltenboeck, Marios D. Demetriou, Joseph P. Schramm, Xiao Liu, Konrad Samwer (a visiting associate from the University of Gottingen, Germany), C. Paul Kim, and Douglas C. Hofmann. This research benefited from support by the II-VI Foundation.

.


Related Links
California Institute of Technology
Space Technology News - Applications and Research






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECH SPACE
Silver cycle: New evidence for natural synthesis of silver nanoparticles
Washington DC (SPX) May 13, 2011
Nanoparticles of silver are being found increasingly in the environment-and in environmental science laboratories. Because they have a variety of useful properties, especially as antibacterial and antifungal agents, silver nanoparticles increasingly are being used in a wide variety of industrial and consumer products. This, in turn, has raised concerns about what happens to them once relea ... read more


TECH SPACE
A Wrinkly Old Reveal Clues To Its Past

MoonBots Challenges Teams to Conduct Lunar Missions with LEGO Robots

Earth's Nearest Neighbor Within Reach

Space Adventures proposes modified Soyuz TMA for Lunar tourists

TECH SPACE
Opportunity Cracks The 18-Mile Mark

Mars Science Laboratory Aeroshell Delivered To Launch Site

Mars Express Sees Deep Fractures on Mars

Opportunity Images Small Craters

TECH SPACE
Heaven is a 'fairy story': Hawking

Putting the Common Housefly onto the dinner plate

JPL Facility has Built Famed Spacecraft for 50 Years

Texas Space Alliance Celebrates New Space "Tourism" Law

TECH SPACE
Top Chinese scientists honored with naming of minor planets

China sees smooth preparation for launch of unmanned module

China to attempt first space rendezvous

Countdown begins for Chineses space station program

TECH SPACE
The Sabatier System: Producing Water on the ISS

Andrews Space Delivers Cargo Module Power Unit for Orbital's Cygnus Spacecraft

ISS orbit to be readjusted for Soyuz TMA-20 return

Soyuz is in the launch zone at Europe's Spaceport

TECH SPACE
Another Ariane 5 begins its assembly at the Spaceport

ST-2's installation on SYLDA marks the start of final payload integration for Ariane 5's next mission

Arianespace to launch ABS-2 in 2013

GSAT-8 put through its paces

TECH SPACE
Flipping Hot Jupiters

What a scorcher: 'Hot Jupiter' puzzle explained

An Earth as Dense as Lead

Astronomers unveil portrait of 'super-exotic super-Earth'

TECH SPACE
Video gaming teens sleep less: study

DAICHI (ALOS) Operations Completed

Making strong, tough metallic glass cheaply

Lessening the Dangers of Radiation




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement