Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Inspired by Nature, Researchers Create Tougher Metal Materials

03.07.2014

Drawing inspiration from the structure of bones and bamboo, researchers have found that by gradually changing the internal structure of metals they can make stronger, tougher materials that can be customized for a wide variety of applications – from body armor to automobile parts.

“If you looked at metal under a microscope you’d see that it is composed of millions of closely-packed grains,” says Yuntian Zhu, a professor of materials science and engineering at NC State and senior author of two papers on the new work. “The size and disposition of those grains affect the metal’s physical characteristics.”


This image illustrates the gradient structure concept. Click to enlarge. Image credit: Yuntian Zhu.

“Having small grains on the surface makes the metal harder, but also makes it less ductile – meaning it can’t be stretched very far without breaking,” says Xiaolei Wu, a professor of materials science at the Chinese Academy of Sciences’ Institute of Mechanics, and lead author of the two papers.

“But if we gradually increase the size of the grains lower down in the material, we can make the metal more ductile. You see similar variation in the size and distribution of structures in a cross-section of bone or a bamboo stalk. In short, the gradual interface of the large and small grains makes the overall material stronger and more ductile, which is a combination of characteristics that is unattainable in conventional materials.

“We call this a ‘gradient structure,’ and you can use this technique to customize a metal’s characteristics,” Wu adds.

Wu and Zhu collaborated on research that tested the gradient structure concept in a variety of metals, including copper, iron, nickel and stainless steel. The technique improved the metal’s properties in all of them.

The research team also tested the new approach in interstitial free (IF) steel, which is used in some industrial applications.

If conventional IF steel is made strong enough to withstand 450 megapascals (MPa) of stress, it has very low ductility – the steel can only be stretched to less than 5 percent of its length without breaking. That makes it unsafe. Low ductility means a material is susceptible to catastrophic failure, such as suddenly snapping in half. Highly ductile materials can stretch, meaning they’re more likely to give people time to respond to a problem before total failure.

By comparison, the researchers created an IF steel with a gradient structure; it was strong enough to handle 500 MPa and ductile enough to stretch to 20 percent of its length before failing.

The researchers are also interested in using the gradient structure approach to make materials more resistant to corrosion, wear and fatigue.

“We think this is an exciting new area for materials research because it has a host of applications and it can be easily and inexpensively incorporated into industrial processes,” Wu says.

The work is described in two recently published papers: “Synergetic Strengthening by Gradient Structure,” which was published online July 2 in Materials Research Letters, and “Extraordinary strain hardening by gradient structure,” which is published in Proceedings of the National Academy of Sciences. The work was supported by the U.S. Army Research Office under grants W911NF-09-1-0427 and W911QX-08-C-0083.

-shipman-

Note to Editors: The study abstracts follow.

“Synergetic Strengthening by Gradient Structure”

Authors: X.L. Wu, P. Jiang, L. Chen, J.F. Zhang and F.P. Yuan, Chinese Academy of Sciences; Y.T. Zhu, North Carolina State University

Published: online July 2, Materials Research Letters

DOI: 10.1080/21663831.2014.935821

Abstract: Gradient structures are characterized with a systematic change in microstructures on a macroscopic scale. Here we report that gradient structures in engineering materials such as metals produce an intrinsic synergetic strengthening, which is much higher than the sum of separate gradient layers. This is caused by macroscopic stress gradient and the bi-axial stress generated by mechanical incompatibility between different layers. This finding represents a new mechanism for strengthening that exploits the principles of both mechanics and materials science. It may provide for a new strategy for designing material structures with superior properties.

“Extraordinary strain hardening by gradient structure”

Authors: X.L. Wu, P. Jiang, L. Chen and F.P. Yuan, Chinese Academy of Sciences; Y.T. Zhu, North Carolina State University

Published: online May 5, Proceedings of the National Academy of Sciences

DOI: 10.1073/pnas.1324069111

Abstract: Gradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures gradually change from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multi-axial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby accumulation and interaction of dislocations are promoted, resulting in an extra hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a novel strategy to develop strong and ductile materials by architecting heterogeneous nanostructures.

Matt Shipman | Eurek Alert!
Further information:
http://news.ncsu.edu/releases/zhu-gradient-structure-2014/

Further reports about: Bamboo COPPER Iron Metal conventional materials materials stainless steel structures technique

More articles from Materials Sciences:

nachricht Triboelectric nanogenerators boost mass spectrometry performance
28.02.2017 | Georgia Institute of Technology

nachricht Nano 'sandwich' offers unique properties
28.02.2017 | Rice 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: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

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...

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

Light-emitting bubbles captured in the wild

28.02.2017 | Physics and Astronomy

Triboelectric nanogenerators boost mass spectrometry performance

28.02.2017 | Materials Sciences

Calculating recharge of groundwater more precisely

28.02.2017 | Ecology, The Environment and Conservation

VideoLinks
B2B-VideoLinks
More VideoLinks >>>