PICATINNY ARSENAL, N.J. -- Two Picatinny Arsenal employees were among a group of inventors who recently received a patent for designing a new nanocomposite as well as developing a method to manufacture it. The employees are Joseph Paras, a materials engineer, and Christopher Haines, a senior metallurgist, both from the Armament Research, Development and Engineering Center or ARDEC.
The other 11 inventors were Enrique J. Lavernia, Julie M. Schoenung, Yizhang Zhou, Zhihui Zhang, Ying Li, Troy Topping, Rustin Vogt (all from the University of California-Davis) and Deepak Kapoor, a contractor.
The new nanocomposite is comprised of non-faceted nanoparticles reinforcing a nanostructured metal matrix. This means that instead of having a large particle with many flat surfaces, similar to a gemstone, the submicron particle portrays a spherical surface that is surrounded by aluminum.
The nanocomposite also has a much smaller grain size than what is currently used. For instance, Small Armor Protective Inserts, ceramic plates that are used in items like body armor, are typically more than 10 microns in grain size.
As a result, this new nanocomposite solves an ongoing challenge with nanostructured materials: the loss of ductility, when the material can deform without breaking. For the warfighter, this means that engineers and scientists could reduce the weight of current vehicular armor materials by using a less dense ceramic material.
Ultimately, continued research could result in materials that could lighten the load for a Soldier's body armor. The average Soldier wears about 37 pounds of ceramic armor on his or her body. The team's new nanocomposite could potentially help to bring that number down below 30 pounds at a minimum.
ENHANCING DUCTILITY
"There is a well-established relationship in science known as the 'Hall Petch' relation that states as the grain size in a material decreases, the strength increases," said Haines.
"Unfortunately, as the strength increases, the ductility decreases. This is what is known as an inverse relationship-- one goes up, the other down--like a lever.
"In developing these materials with University of California - Davis, we came up with the idea to incorporate some of ARDEC's boron carbide nanopowder into a nanomaterial as a reinforcing, or strengthening, phase along with some coarse grained material, which enhanced the ductility," explained Haines. "The simultaneous addition of these materials to the already nano-structured aluminum led to substantial increases in strength, while maintaining ductility. So, we got the best of both worlds."
The team's idea was inspired by a lack of scientific research about using ceramic nanoparticles as a reinforcement phase in light metals, such as aluminum and magnesium. In the past, only conventional (large and faceted) ceramic particles have been used.
LESSONS LEARNED
Since the first publication of their nano-research, however, the team's article ("Mechanical behavior of ultrafine-grained Al composites reinforced with B4C nanoparticles" in Scripta Materialia, Volume 65, Issue 8) has been cited 35 times.
"We know that we produce nanomaterials at ARDEC that are superior to materials available commercial-off-the-shelf, but because of that, we often cannot predict performance," said Haines.
"For instance, we learned that our boron carbide nanopowder, if not stored properly, can start to degrade over time. This is not true with conventional (micron sized) boron carbide powder, but the high surface area associated with our powders makes it very susceptible to reaction with moisture and oxygen.
"When this occurs, it has a negative effect on the performance when used in these materials," added Haines.
"This is a very important finding. In fact, we have some collaborative research and development being performed at the University of Pittsburgh to understand the nature of this aging phenomenon."
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The U.S. Army Armament Research, Development and Engineering Center 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.
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