At the U.S. Army Research Laboratory, scientists are on the hunt for nanomaterials that will improve engine technology in a big way.
“What we’re seeing is a revolutionary property arising in a class of materials that we never thought was possible,” said Dr. Kristopher A. Darling, a materials scientist with the laboratory’s Lightweight and Specialty Metals Branch.
Darling and his team of collaborators published new findings in the journal Nature that he says were totally unexpected.
“The properties that we’re seeing are startling I would say,” he said. “They have the potential to revolutionize a lot of potential applications.”
In the Nature paper, Extreme creep resistance in a microstructurally stable nancrystalline alloy, published Sept. 14, 2016, Darling outlines how they stabilized a copper alloy microstructure and found it to be strong at very high temperatures.
“Normally this wouldn’t happen,” he said. “We’re trying to make microstructures survive at the high temperatures of consolidation.”
Inside turbine engines, temperatures can soar to more than 2,500�F. Army scientists are focused on developing new bulk-structured nanomaterials that are stabilized to high temperatures.
“The DOD heavily depends on jet turbine engines where you would have to have high-structural strength with high thermal stability,” Darling said. “This particular material is copper, which is not a type of material that you wouldn’t necessarily use in an engine, but what it demonstrates is that these types of microstructures are capable of achieving properties that are extraordinarily high in comparison to what you would normally see in a conventional type of material.”
The team hopes to be able to pass the properties on to other types of materials.
“If we could do this in other materials like nickel, cobalt or tantalum, it would definitely have a chance of revolutionizing engine technology,” he said. “What’s unique about this article is that it’s a very unique finding, in that it takes what is currently known about the material systems that I work in and sort of flips it on its head and says that things that people thought were impossible are possible. Now we have high strength at high temperature.”
Darling said it’s all about creep response, or how materials deform under continuous stress at elevated temperatures.
“We’re seeing orders of magnitude improvements in the creep response,” he said. “There is a six to eight orders of magnitude increase in creep response relative to what conventional nanocrystal materials can do.”
This finding left the scientists scratching their heads, he said.
“We did the preliminary tests here and we didn’t get what we were expecting,” Darling said. “A lot of times unique discoveries are made by accident or by sheer luck, and this was one of those cases where we started to probe the material and we didn’t see the response that we were expecting.”
Darling reached out to colleagues at the University of North Texas and Arizona State University to help make sure what they were observing was correct.
“Frankly when I talked with them, they didn’t believe it either,” he said. “We’re seeing these properties and they said there’s no way that this could be possible. They began to test the samples themselves and then they were amazed. From there, all the excitement grew and we started doing more thorough studies. Ultimately it led to writing this paper.”
Darling has been studying this material for about five years. He started working at the laboratory after earning his doctoral degree from North Carolina State University in 2009.
“Initially it started off about the time I was a postdoc,” he said. “There have been a number of people within the Army Research Lab, specifically Drs. Lazlo Kecskes, Chad Hornbuckle, and Mark Tschopp, who were heavily involved initially in the research projects and still are, additionally, Mr. Tom Luckenbaugh, Mr. Anthony Roberts, and Mr. Micah Gallagher have been critical to engineering this specific alloy. Previously, published work on this alloy, led to being introduced into some of the university collaborators that we work with now, specifically Prof. Kiran Solanki at Arizona State and Prof. Rajiv Mishra at University of North Texas. They’ve been heavily involved in doing some of the mechanical testing and characterization. It’s been a real group effort.”
This was a first attempt, Darling said. The team hopes to maximize the property, or engineer it to its finest extent.
“We could still see large improvements in understanding how to manipulate the microstructure to improve the properties even further,” he said.
Nanotechnology research in metals is a relatively young field, he said. Going back just a couple of decades, people were just learning how to synthesize these materials in bulk form and trying to understand the basic fundamental properties of these materials.
“What we’re showing in this paper is that these materials show properties reminiscent of the properties reported with nickel-based single crystals. The results are shocking in the sense that the behavior is so much better than what you would expect from a material like this,” Darling said. “Materials like this could possibly open a door to revolutionizing engine technology, which would be of benefit to the Army as well as civilian applications.”
Filed Under: Aerospace + defense