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 Twisting magnets enhance data storage capacity
12.02.2016 | Hiroshima University

nachricht A metal that behaves like water
12.02.2016 | Harvard John A. Paulson School of Engineering and Applied Sciences

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Production of an AIDS vaccine in algae

Today, plants and microorganisms are heavily used for the production of medicinal products. The production of biopharmaceuticals in plants, also referred to as “Molecular Pharming”, represents a continuously growing field of plant biotechnology. Preferred host organisms include yeast and crop plants, such as maize and potato – plants with high demands. With the help of a special algal strain, the research team of Prof. Ralph Bock at the Max Planck Institute of Molecular Plant Physiology in Potsdam strives to develop a more efficient and resource-saving system for the production of medicines and vaccines. They tested its practicality by synthesizing a component of a potential AIDS vaccine.

The use of plants and microorganisms to produce pharmaceuticals is nothing new. In 1982, bacteria were genetically modified to produce human insulin, a drug...

Im Focus: The most accurate optical single-ion clock worldwide

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far. Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18. The results have been published in the current issue of the scientific journal "Physical Review Letters".

Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock...

Im Focus: Goodbye ground control: autonomous nanosatellites

The University of Würzburg has two new space projects in the pipeline which are concerned with the observation of planets and autonomous fault correction aboard satellites. The German Federal Ministry of Economic Affairs and Energy funds the projects with around 1.6 million euros.

Detecting tornadoes that sweep across Mars. Discovering meteors that fall to Earth. Investigating strange lightning that flashes from Earth's atmosphere into...

Im Focus: Flow phenomena on solid surfaces: Physicists highlight key role played by boundary layer velocity

Physicists from Saarland University and the ESPCI in Paris have shown how liquids on solid surfaces can be made to slide over the surface a bit like a bobsleigh on ice. The key is to apply a coating at the boundary between the liquid and the surface that induces the liquid to slip. This results in an increase in the average flow velocity of the liquid and its throughput. This was demonstrated by studying the behaviour of droplets on surfaces with different coatings as they evolved into the equilibrium state. The results could prove useful in optimizing industrial processes, such as the extrusion of plastics.

The study has been published in the respected academic journal PNAS (Proceedings of the National Academy of Sciences of the United States of America).

Im Focus: New study: How stable is the West Antarctic Ice Sheet?

Exceeding critical temperature limits in the Southern Ocean may cause the collapse of ice sheets and a sharp rise in sea levels

A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Symposium on Climate Change Adaptation in Africa 2016

12.02.2016 | Event News

Travel grants available: Meet the world’s most proficient mathematicians and computer scientists

09.02.2016 | Event News

AKL’16: Experience Laser Technology Live in Europe´s Largest Laser Application Center!

02.02.2016 | Event News

 
Latest News

LIGO confirms RIT's breakthrough prediction of gravitational waves

12.02.2016 | Physics and Astronomy

Gene switch may repair DNA and prevent cancer

12.02.2016 | Life Sciences

Using 'Pacemakers' in spinal cord injuries

12.02.2016 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>