New technique allows closer study of how radiation damages materials

Aug 06, 2013 by Matt Shipman
Researchers at NC State University used high-resolution transmission electron microscopy to simultaneously irradiate magnesium and collect images of voids forming in the material. Credit: Weizong Xu

A team of researchers led by North Carolina State University has developed a technique that provides real-time images of how magnesium changes at the atomic scale when exposed to radiation. The technique may give researchers new insights into how radiation weakens the integrity of radiation-tolerant materials, such as those used in space exploration and in nuclear energy technologies.

"We used high-resolution (HRTEM) to simultaneously irradiate the magnesium and collect images of the material at the ," says Weizong Xu, a Ph.D. student at NC State and lead author of a paper describing the work. "It is a new way to use an existing technology, and it allowed us to see voids forming and expanding in the material.

"Prior to this, we knew radiation could cause voids that weaken the material, but we didn't know how the voids formed," Xu says. Voids are physical gaps in materials that begin at the and can cause a material to swell or crack.

The researchers looked at magnesium for two reasons. First, magnesium's atoms arrange themselves into tightly packed layers in a .

"This is important, because many radiation-tolerant materials have the same structure – including , which is widely used in research on radiation-tolerant materials such as those used in ," says Dr. Suveen Mathaudhu, a co-author of the paper and adjunct assistant professor of materials science and engineering at NC State under the U.S. Army Research Office's Staff Research Program.

The second reason they chose magnesium is because it takes less energy to cause void formation in magnesium than in other materials with similar structures, such as zirconium. This lower energy threshold is what allowed researchers to use HRTEM to trigger void formation and capture atomic-scale images of the process with the same microscopy beam.

A team of researchers led by North Carolina State University has developed a technique that provides real-time images of how voids form in materials when they are exposed to radiation. This image shows a void forming in magnesium. Credit: Weizong Xu

"You couldn't use this technique on zirconium, for example," Mathaudhu says. "But what we're learning about void formation gives us insight into how radiation damages these kinds of materials.

"In addition to any energy applications, we need to develop new radiation-tolerant materials if we want to explore deep space," Mathaudhu says. "This may move us one step closer to that goal."

"If we can improve our understanding of the mechanisms behind void formation, we can begin developing materials to control the problem," says Dr. Yuntian Zhu, a professor of at NC State and senior author of the paper.

Explore further: Scaling up armor systems

More information: The paper, "In-situ atomic-scale observation of irradiation-induced void formation," was published online Aug. 5 in Nature Communications. www.nature.com/ncomms/2013/130… full/ncomms3288.html

Abstract
The formation of voids in an irradiated material significantly degrades its physical and mechanical properties. Void nucleation and growth involve discrete atomic-scale processes that, unfortunately, are not yet well understood due to the lack of direct experimental examination. Here we report for the first time in-situ atomic-scale observation of the nucleation and growth of voids in hexagonal close-packed magnesium under electron irradiation. The voids are found to first grow into a plate-like shape, followed by a gradual transition to a nearly equiaxial geometry. Using atomistic simulations, we show that the initial growth in length is controlled by slow nucleation kinetics of vacancy layers on basal facets and anisotropic vacancy diffusivity. The subsequent thickness growth is driven by thermodynamics to reduce surface energy. These experiments represent unprecedented resolution and characterization of void nucleation and growth under irradiation, and might help with understanding the irradiation damage of other hexagonal close-packed materials.

Related Stories

Recommended for you

Galaxy dust findings confound view of early Universe

Jan 31, 2015

What was the Universe like at the beginning of time? How did the Universe come to be the way it is today?—big questions and huge attention paid when scientists attempt answers. So was the early-universe ...

Evidence mounts for quantum criticality theory

Jan 30, 2015

A new study by a team of physicists at Rice University, Zhejiang University, Los Alamos National Laboratory, Florida State University and the Max Planck Institute adds to the growing body of evidence supporting ...

Scaling up armor systems

Jan 30, 2015

Dermal modification is a significant part of evolution, says Ranajay Ghosh, an associate research scientist in the College of Engineering. Almost every organism has something on its skin that provides important ...

Seeking cracks in the Standard Model

Jan 30, 2015

In particle physics, it's our business to understand structure. I work on the Large Hadron Collider (LHC) and this machine lets us see and study the smallest structure of all; unimaginably tiny fundamental partic ...

The first optically synchronised free-electron laser

Jan 30, 2015

Scientists at DESY have developed and implemented an optical synchronisation system for the soft X-ray free-electron laser FLASH, achieving facility-wide synchronisation with femtosecond precision. The performance ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.