Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cyclic healing removes defects in metals while maintaining strength

20.10.2015

When designing a new material, whether for an airplane, car, bridge, mobile device, or biological implant, engineers strive to make the material strong and defect-free. However, methods conventionally used to control the amount of defects in a material, such as applying heat or mechanical stress, can also have undesirable consequences in terms of the material's strength, structure and performance.

An international team of researchers, including Carnegie Mellon University President Subra Suresh, Zhiwei Shan and colleagues from Xi'an Jiaotong University in China, Ming Dao and Ju Li from MIT, and Evan Ma from Johns Hopkins University, has developed a new technique called cyclic healing that uses repetitive, gentle stretching to eliminate pre-existing defects in metal crystals.


These are bright-field images of aluminum single crystal before (top) and after mechanical healing (bottom).

Credit: MIT

Their results have been published online today (Monday, Oct. 19) in the Proceedings of the National Academy of Sciences.

Most materials are made of crystals. When materials fail, it is usually the result of defects in the crystal or in the arrangement of multiple crystals in a polycrystalline structure. While much research has been done on metal fatigue at larger scales, new technologies are just now allowing researchers to see how atomic-scale defects nucleate, multiply and interact in materials subjected to monotonic or fatigue loading inside a high-resolution microscope.

In this study, the researchers used transmission electron microscopy to look inside sub-micrometer-sized specimens of aluminum crystals as they subjected the samples to stressors like repeated, small-amplitude deformation or fatigue loading.

They found that gentle cyclic deformation, a process that repetitively stretches the crystal, helps to unpin or shakedown rows of atomic defects known as dislocations in the metal and move these dislocations closer to free surfaces in the sample.

Image forces, which act to minimize the energy of the defects, attract the dislocations closer to the free surfaces and force them out of the crystal. As a result, the crystal "heals," becoming essentially free of pre-existing dislocations, thereby significantly increasing its strength.

This finding was surprising to researchers because cyclic deformation has an opposite effect in micro- and macro-scale metal crystals. In these larger samples, repeated stretching generally leads to the creation, accumulation and interaction of defects, which can lead to cracking and failure.

"This work demonstrates how cyclic deformation, under certain controlled conditions, can lead to the removal of defects from crystals of small volume," says Suresh, who holds the Henry L. Hillman President's Chair at CMU. "It also points to potential new pathways for engineering the defect structure of metal components in a variety of sub-micro-scale systems."

###

The research was supported by the National Science Foundation (DMR-1120901 and DMR-1410636) , the 973 Programs of China, the U.S. Department of Energy, and the Singapore-MIT Alliance for Research and Technology.

Media Contact

Jocelyn Duffy
jhduffy@andrew.cmu.edu
412-268-9982

 @CMUScience

http://www.cmu.edu 

Jocelyn Duffy | EurekAlert!

More articles from Materials Sciences:

nachricht Using a simple, scalable method, a material that can be used as a sensor is developed
15.02.2017 | University of the Basque Country

nachricht New mechanical metamaterials can block symmetry of motion, findings suggest
14.02.2017 | University of Texas at Austin

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

Biocompatible 3-D tracking system has potential to improve robot-assisted surgery

17.02.2017 | Medical Engineering

Real-time MRI analysis powered by supercomputers

17.02.2017 | Medical Engineering

Antibiotic effective against drug-resistant bacteria in pediatric skin infections

17.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>