Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study may expand applied benefits of super-hard ceramics

05.08.2005


A discovery reported in the August 5 issue of Science could speed the design of materials that approach the hardness of diamond yet remain supple enough to be worked like metal.



In a massive computer simulation involving 128 computer processors and nearly 19 million atoms, materials scientist Izabela Szlufarska of the University of Wisconsin-Madison and colleagues at University of Southern California demonstrated the precise atomic mechanisms that explain why "nanostructured" ceramic materials-some of the hardest substances known-also exhibit unusual pliability.

Unlike other exceptionally hard materials, these advanced ceramics tend to bend rather than break, meaning they could be shaped into extremely long-lasting yet lightweight parts for everything from automobile engines and high-speed machining tools to medical implants in the body.


But they are also notoriously difficult to engineer, because as their name implies they possess a grain structure that falls into the nano-size range of molecules and atoms.

"How to optimize their design is an open question," says Szlufarska, who is also a professor of engineering physics. "People have used a trial and error approach to make these materials harder. But there is still much to be understood as to why they are harder."

Simulations can help to answer this by providing a level of detail unavailable to experiments. Using atomic-scale simulations, the team observed for the first time how atoms moved and interacted as a super-hard ceramic deformed under stress. The advance has not only provided unprecedented insight into the properties of these materials, but also a tool that researchers can use to systematically nano-engineer them.

"This study is just the first step," says Szlufarska. "The goal is to design the strongest material possible."

The particular nanostructured ceramic Szlufarska focuses on, called nanocrystalline silicon carbide, is also exceptionally resistant to high temperature and radiation, which has NASA eyeing it as a coating for the space shuttle. Another important application is micro-electro mechanical systems (MEMS), tiny machines that are currently made of silicon.

"Today’s MEMS can’t have two surfaces rubbing against one another because the silicon is brittle and tends to break," says Szlufarska. "If we could instead make MEMS out of silicon carbide, the sky would be the limit in terms of applications." Normal ceramics, like clays, become brittle when fired. But when ceramic is made from particles spanning mere atoms in diameter, the material exhibits dramatically improved ductility after bonding at high temperature and pressure.

This unusual combination of strength and suppleness is derived from the material’s two-phase nature. In nanocrystalline silicon carbide, says Szlufarska, highly ordered, crystalline grains are surrounded by a more disordered, or amorphous, matrix of grain boundaries-much like tiny stones cemented by a semi-fluid mortar. And the volume of grain boundaries exceeds that in other nanostructured materials such as metals.

To understand, at the atomic scale, how nanocrystalline silicon carbide deforms under force, the team performed a simulation in which they pressed a tiny, virtual probe, called an indenter, into the material’s surface and watched how the atoms moved in response. Initially, the grains deformed and then sprang back as a unit, an illustration of the material’s hardness.

"At this point, the grains all moved together because the grain boundaries held them together like glue," says Szlufarska.

But as the probe pressed deeper and exerted greater pressure, the researchers witnessed a surprising shift in the material’s response. At a specific indentation depth, the grain boundaries began to yield, allowing individual grains to rotate and glide independently under the probe’s force.

"Because the grain boundaries are flowing, the material is more ductile than normal ceramic would be," says Szlufarska. "And the grain boundaries initially take part of the deformation, so in essence they protect the grains from breaking."

In contrast, nano-structured metals go through no such phase; instead their grains take the brunt of the force, immediately developing defects, like tiny cracks, when the material begins to yield.

"Once defects occur in the system, the system is just weaker and it’s going to break," says Szlufarska.

This crossover in response-from cooperative grain movement and hardness, to individual movement and ductility-is unique to nano-structured ceramics, she says. The researchers next want to learn how to control the crossover point so as to engineer greater hardness into nano-crystalline silicon carbide without compromising pliability. For example, they could vary the volume of the grain boundaries or the size of the grains. Impurities, or dopants, might also be added to the grain boundaries to make the material stronger.

Key to it all is the enormous computing power that allows scientists to simulate the material’s atomic details.

"The experiments and devices have become smaller and smaller, while the simulations have grown larger and larger," says Szlufarska. "This is a unique time when the leading edge of materials design is exactly at the same length scale where fully atomic simulations are possible."

Izabela Szlufarska | EurekAlert!
Further information:
http://www.wisc.edu

More articles from Materials Sciences:

nachricht Serendipity uncovers borophene's potential
23.02.2017 | Northwestern University

nachricht Switched-on DNA
20.02.2017 | Arizona State University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

NASA eyes Pineapple Express soaking California

24.02.2017 | Earth Sciences

New gene for atrazine resistance identified in waterhemp

24.02.2017 | Agricultural and Forestry Science

New Mechanisms of Gene Inactivation may prevent Aging and Cancer

24.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>