Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Twinning phenomenon found in nanocrystalline aluminum

31.07.2003


Using a powerful electron microscope to view atomic-level details, Johns Hopkins researchers have discovered a "twinning" phenomenon in a nanocrystalline form of aluminum that was plastically deformed during lab experiments. The finding will help scientists better predict the mechanical behavior and reliability of new types of specially fabricated metals. The research results, an important advance in the understanding of metallic nanomaterials, were published in a recent issue of the journal Science.



At the microscopic level, most metals are made up of tiny crystallites, or grains. Through careful lab processing, however, scientists in recent years have begun to produced nanocrystalline forms of metals in which the individual grains are much smaller. These nanocrystalline forms are prized because they are much stronger and harder than their commercial-grade counterparts. Although they are costly to produce in large quantities, these nanomaterials can be used to make critical components for tiny machines called microelectromechanical systems, often referred to as MEMS, or even smaller nanoelectromechanical systems, NEMS.

But before they build devices with nanomaterials, engineers need a better idea of how the metals will behave. For example, under what conditions will they bend or break? To find out what happens to these new metals under stress at the atomic level, Johns Hopkins researchers, led by Mingwei Chen, conducted experiments on a thin film of nanocrystalline aluminum. Grains in this form of aluminum are 1,000th the size of the grains in commercial aluminum.


Chen and his colleagues employed two methods to deform the nanomaterial or cause it to change shape. The researchers used a diamond-tipped indenter to punch a tiny hole in one piece of film and subjected another piece to grinding in a mortar. The ultra-thin edge of the punched hole and tiny fragments from the grinding were then examined under a transmission electron microscope, which allowed the researchers to study what had happened to the material at the atomic level. The researchers saw that some rows of atoms had shifted into a zig-zag pattern, resembling the bellows of an accordion. This type of realignment, called deformation twinning, helps explain how the nanomaterial, which is stronger and harder than conventional materials, deforms when subjected to high loads.

"This was an important finding because deformation twinning does not occur in traditional coarse-grain forms of aluminum," said Chen, an associate research scientist in the Department of Mechanical Engineering in the university’s Whiting School of Engineering. "Using computer simulations, other researchers had predicted that deformation twinning would be seen in nanocrystalline aluminum. We were the first to confirm this through laboratory experiments."

By seeing how the nanomaterial deforms at the atomic level, researchers are gaining a better understanding of why these metals do not bend or break as easily as commercial metals do. "This discovery will help us build new models to predict how reliably new nanoscale materials will perform when subjected to mechanical forces in real-world devices," said Kevin J. Hemker, a professor of mechanical engineering and a co-author of the Science paper. "Before we can construct these models, we need to improve our fundamental understanding of what happens to nanomaterials at the atomic level. This is a key piece of the puzzle."

The nanocrystalline aluminum used in the experiments was fabricated in the laboratory of En Ma, a professor in the Department of Materials Science and Engineering and another co-author of the research paper. "This discovery nails down one deformation process that occurs in nanocrystalline metals," Ma said. "This is the first time a new mechanism, which is unique to nanostructures and improbable in normal aluminum, has been conclusively demonstrated."

Other co-authors of the paper were Hongwei Sheng, an associate research scientist in the Department of Materials Science and Engineering; Yinmin Wang, a graduate student in the Department of Materials Science and Engineering; and Xuemei Cheng, a graduate student in the Department of Physics and Astronomy.

Phil Sneiderman | EurekAlert!
Further information:
http://www.me.jhu.edu

More articles from Physics and Astronomy:

nachricht Subaru Telescope helps pinpoint origin of ultra-high energy neutrino
16.07.2018 | National Institutes of Natural Sciences

nachricht Nano-kirigami: 'Paper-cut' provides model for 3D intelligent nanofabrication
16.07.2018 | Chinese Academy of Sciences Headquarters

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Subaru Telescope helps pinpoint origin of ultra-high energy neutrino

16.07.2018 | Physics and Astronomy

Barium ruthenate: A high-yield, easy-to-handle perovskite catalyst for the oxidation of sulfides

16.07.2018 | Life Sciences

New research calculates capacity of North American forests to sequester carbon

16.07.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>