Army scientists think big, go small

August 22, 2018

By ARL Public Affairs

ABERDEEN PROVING GROUND, Md. (Aug. 21, 2018) -- When material scientists from the U.S. Army Research Laboratory think big, they start by exploring the world of the really small.

Using state-of-the-art technology and tools, Army scientists are analyzing metal and ceramic specimens at the atomic level.

To get an idea of the size they're working with, imagine the width of a hair. The samples are a thousand times smaller than the end of a strand of human hair.

The atom probe, researchers said, has become a key to understanding the structure of materials.

"The atom probe gives us a 3-D reconstruction at the atomic level," said Dr. Chad Hornbuckle, a materials scientist with the laboratory's Weapons and Materials Research Directorate. "When you see the reconstruction that's made up of millions of dots, the dots are actually individual atoms."

Hornbuckle, whose specialty is microstructural characterization using electron microscopes and atom probe tomography, or APT, said the technology sets the standard for accuracy in chemistry. "It's basically the only machine in the world that can do this at the atomic level," he said. "There are machines, like transmission electron microscopes, or TEMs, that do chemical analysis, but it is not as accurate as this."

Accuracy is important, he said, because consistency is vital in experimentation.

"You might have one effect one time, but if the chemistry changes, you get a completely different effect the next time," he said. "If you can't control the chemistry, you can't control the properties."

Again, the nanoscale is really small. If you take a meter and divide it by 109 you have one nanometer. Researchers prepare samples for analysis by creating really sharp tips basically sandblasting, or milling materials away, with the chemical element gallium using a dual beam scanning electron microscope or focused ion beam microscope. Once the samples are ready, Hornbuckle carefully inserts them into the atom probe.

He mastered the device when he was a graduate student with the University of Alabama's Department of Metallurgical and Materials Engineering. Now, Army scientists regularly come to him to characterize their samples. Using APT, they discover what atoms are present in a material and their location within a material.

Inside the probe, the samples are in a super cold vacuum. Using a laser, or a voltage pulse, the scientists ionize the atoms within the small tip causing the individual ions to field evaporate from the surface. The evaporated ions are analyzed and identified, providing a 3-D model at near-atomic spatial resolution.

"I can give you one specific example of how it's helped our research," said Dr. Denise Yin, a postdoctoral fellow at the lab and graduate of Lehigh University. "We were electrodepositing copper in a magnetic field and we found a chemical phase using the atom probe that didn't otherwise show up in conventional electrodeposition.

Electrodeposition is a process that creates a thin metal coating.

We were having problems identifying this phase using other methods, but the atom probe told us exactly what it was and how it was distributed."

The machine's capability is impressive, she said.

"You can see the atoms show up in real time," Yin said. "Again, it's at the nanometer scale, so it's much finer than all the other characterization techniques. The atom probe told us quite easily that the unknown phase was two different types of a copper hydride phase, and that's not something that we could have detected using those other methods."

The kind of atom probe the Army uses is one of only a handful found across the nation.

Since there are a limited number of atom probes, universities are very interested in utilizing it to analyze some of their own samples, Hornbuckle said.

"One university that we collaborate with is Lehigh University," he said. "At first, this collaboration was more of a mutual exchange of expertise, where I analyzed some of their samples in the atom probe and they used their aberration-corrected transmission electron microscope to analyze some of our copper-tantalum sample. We now have a cooperative agreement with them to continue this collaboration."

The laboratory seeks formal agreements as part of its Open Campus business model.

"Open Campus means sharing world-class ARL facilities and research opportunities for our partners," said ARL Director Dr. Philip Perconti. "A thriving Open Campus program increases opportunities for technology advancement and the transfer of research knowledge."

The partnership with Lehigh delivered important results.

"I actually ran a nickel-tungsten alloy that was electrodeposited for them and identified and quantified the presence of low atomic number elements such as oxygen and sodium," Hornbuckle said. "This resulted in one research journal article with several more in preparation."

Hornbuckle said the Army is also working with the University of Alabama.

"They have a different version of the atom probe," he said. "They have run some our alloys in their version and ours to compare the differences noted in the same material. This material is actually being scaled up through a number of processes that are relevant to the Army."

This collaboration also resulted in numerous research journal articles, Hornbuckle said. "We also have a partnership with them."

Another university collaborating with the Army with is Texas A&M.

"This collaboration initiated due to the Open Campus initiative," Hornbuckle said. "I have analyzed a few nickel-titanium alloys that had been 3-D printed. They noticed some nanoscale precipitates within the 3-D printed materials, but were unable to identify them with their TEM. I am trying to determine the chemistry of the phase using the atom probe, which should help to identify it."

These partnerships give the Army access to equipment available at these universities that the laboratory does not possess, and creates a connection to the university that facilitates access. The fundamental knowledge gained through this research is then applied to current Army problems and in the development to future Army relevant materials, Hornbuckle said.

"When you see things no other human has ever seen before, it's very cool to think that I'm helping to push the envelope of new modern materials science, which then obviously is used for the Army," Hornbuckle said. "Every time we run a new material we think about how we can help the Soldier with this new discovery."


The U.S. Army Research Laboratory is part of the U.S. Army Research, Development and Engineering Command, which has the mission to ensure decisive overmatch for unified land operations to empower the Army, the joint warfighter and our nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.

 

Last Update / Reviewed: August 22, 2018