Scientists are getting rid of the mystery of how radiation weakens a metal, one atom at a time

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Analyze GB and its surroundings. (a) Instrumental crystal orientation mapping showing grain orientations in the vicinity of the interface of interest. The boundary of interest separates the two indicated grains, labeled A and B, in the center of the image (B) and terminates at the triple intersections. [labeled TJ in (C)]. Limit faces are defined on 3 {112} interfaces that intersect at 120°. (d) High-angle annular dark field scanning transmission electron microscope image showing the structure at atomic resolution. (e) the atomic model [embedded atom method (EAM)] For the perfect face and crosshair structure. Fast Fourier Transform Analysis of Atomic Resolution Images [inset in (D)] It shows that the grain rotates 3.2° from the Σ3 exact direction. attributed to him: science progress (2022). DOI: 10.1126 / sciadv.abn0900

Gray and white spots intermittently glide over the computer screen. Looming a microscope towering over a kaleidoscope of electronic and optical equipment. Inside the microscope, high-energy, accelerating ions bombard a piece of platinum thinner than a hair on a mosquito’s back. Meanwhile, a team of scientists is studying the seemingly chaotic display, looking for clues to explain how and why materials degrade in harsh environments.

These Sandia-based scientists believe the key to preventing catastrophic large-scale failures of bridges, aircraft and Power plants is to look closely at damage as it appears for the first time at the atomic and nanoscale levels.

“As human beings, we see physical space around us, and imagining that everything is permanent,” said Sandia materials scientist, Brad Boyce. We see the table, the chair, the lamp, the lights, and imagine that he will always be there, and he is stable. But we also have this human experience that things around us can break unexpectedly. This is proof that these things are not really stable at all. The truth is that many of the materials around us are unstable.”

But the basic truth about how failure starts from the atom is largely a mystery, especially in complexity, harsh environments such as a space or a fusion reactor or a nuclear power plant. The answer is obscured by the complex and interrelated processes that require a combination of specialized expertise to sort.

The team recently published in the magazine science progress Findings of the destabilizing effects of radiation. While the results describe how metals degrade from a fundamental perspective, the results can help engineers predict the material’s response to different types of damage and improve materials reliability in intense radiation environments.

For example, by the time a nuclear power plant reaches retirement age, the pipes, cables, and containment systems inside the reactor can be dangerously brittle and vulnerable. Decades of exposure to heat, stress, vibration and a constant barrage of radiation are shattering materials faster than usual. Previously strong structures have become unreliable and unsafe, only suitable for decontamination and disposal.

“If we can understand these mechanisms and make sure that future materials are adapted, essentially, to reduce these degradation pathways, maybe we can get more life out of the materials we depend on, or at least predict better when they go,” Brad said.

The research was conducted, in part, at the Center for Integrated Nanotechnology, a Office of Science user facility operated for the Department of Energy by Sandia and Los Alamos National Laboratories.

Atomic-scale research can protect metals from damage

Metals and ceramics consist of microscopic crystals also called grains. The smaller the crystals, the stronger the material. Scientists have already shown that it is possible to strengthen the metal by engineering incredibly small nanocrystals.

“You can take pure copper, and by treating it so that it becomes nanoparticles, it can become as strong as some steels,” Brad said.

But the radiation permanently destroys and changes the crystal structure of the grains, weakening the minerals. A single radioactive particle hits a metal crystal like a billiard ball that precisely smashes a group of billiard balls, said Remy Dangerville, a computer simulation and theory expert on the team. Radiation may only hit one atom upside down, but that atom sticks out and collides with the others in a chaotic domino effect.

Unlike the main sphere, the radiation particles pack so much heat and energy that they can temporarily melt the spot they hit, which also weakens the metal, Remy said. And in highly radioactive environments, structures survive an endless hailstorm of these particles.

The Sandia team wants to slow – or even stop – the changes to the atomic scale of the metals caused by the radiation. To do this, researchers act as forensic investigators who replicate crime scenes to understand real scenes. Their Science Advances paper details an experiment in which they used highly customized, high power Electron microscope Watch the damage in the platinum metal grains.

Team member Khaled Hattar has modified and upgraded this microscope for more than a decade, and is currently at the Irradiation Laboratory at Sandia. This unique instrument can expose materials to all types of elements – including heat, cryogenic cold, mechanical stress, a range of controlled radiation, and chemical and electrical environments. It allows scientists to view the occurrence of degradation microscopically, in real time. Sandia’s team combined these dynamic observations with a higher magnification microscope allowing them to see the atomic structure of the intergranular boundaries and determine how radiation changes them.

But such criminal action is fraught with challenges.

“I mean, these are really tough problems,” said Doug Medellin, another Sandia team member. Brad enlisted Doug’s help on the project because of his deep expertise in analyzing grain boundaries. Doug has been studying similar problems since the 1990s.

“We start with a sample that’s maybe three millimeters in diameter when glued to the electron microscope,” Doug said. “Then we zoom in to dimensions only a few atoms wide. And so, there’s just this practical side of: How do you go and find things before and after the experiment? And then, how do you make sense of those atomic arrangements in a meaningful way?”

By combining atomic-scale images with nano-video collected during the experiment, the team discovered that platinum irradiation causes the boundaries between grains to move.

العلماء يبتعدون عن لغز معدني ، ذرة واحدة في كل مرة

Evolution of Σ3 Gb during in situ TEM ion irradiation. (a) Pre-irradiation, (b) 0.3 dB, and (c) 1 dB. (I-VI) A series of fixed frames taken from TEM on site. Movie S1 (0.369 to 0.459 dpa) shows the local interaction between irradiation-induced defects (external to GB) and the Σ3{112} GB facets. attributed to him: science progress (2022). DOI: 10.1126 / sciadv.abn0900

Computer simulations help explain cause and effect

After the experiment, the next challenge was to translate what they saw in the photos and video into mathematical models. This is difficult when some of the atoms are dislodged due to physical collisions, while others may move due to localized heating. To separate the effects, empiricists turn to theorists such as Remy.

“Simulating radiation damage at the atomic level is very (computationally) expensive,” Remy said. Because there are so many moving atoms, it takes a lot of time and processing power on high-performance computers to model the damage.

He said Sandia has some of the best modeling capabilities and experience in the world. Researchers typically measure the amount of radiation damage to a material in units called displacements per atom, or dpa for short. Typical computer models can simulate up to 0.5 decibels of damage. Sandia models can simulate up to 10 times that, which is about 5 dpa.

In fact, the combination of in-house expertise in atomic microscopy, the ability to reproduce extreme radiation environments and this niche specializing in computer modeling makes Sandia one of the few places in the world where this research can be conducted, Remy said.

But even advanced Sandia software can simulate only a few seconds radiation ruin. A better understanding of the basic processes will require hardware and software that can simulate longer periods of time. Brad said humans have been making and breaking metals for centuries, so the remaining knowledge gaps are complex, and require teams of experts to spend years honing their skills and refining their theories. Doug said the long-term nature of research is one of the things that has drawn him into this field of work for nearly 30 years.

“I think that’s what drives me,” he said. “It’s this itch to find out, and it takes a long time to find out.”

Using electron microscopy and automatic atomic tracking to learn more about grain boundaries in metals during deformation

more information:
Christopher M. Barr et al., Irradiation-induced grain boundary face motion: in situ observations and atomic scale mechanisms, science progress (2022). DOI: 10.1126 / sciadv.abn0900

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