NRL Researchers Push Nanoscience Boundaries to Lighten, Strengthen Warfighter Armor

A multi-disciplinary team of researchers at the U.S. Naval Research Laboratory (NRL) pushed grain size engineering to the limit and recently discovered previously unseen behaviors in nanocrystalline ceramics that could lead to the design of better performing ceramic armor.

The discovery, a continuation of NRL research published in 2014, was made possible by a cutting-edge nanosintering technique, which is the process of essentially bonding nano-sized particles together.

"A few years ago, NRL was the first to show that if you decrease the grain size of ceramics to tens of nanometers, the hardness and strength increase," said Dr. James Wollmershauser, a materials research engineer in NRL's Materials Science and Technology Division. "Our current work takes this much further. We decreased the grain size of fully dense ceramics to record breaking single digits, and analyzed the elasticity, hardness, energy dissipation and fracture behavior in ceramics with a wide range of nanosize grains."

Dr. Heonjune Ryou, a postdoctoral fellow in NRL's Chemistry Division, characterized the mechanics of the nanocrystalline ceramics and found that they accommodate mechanical energy in a unique way. This aspect had never been seen before in bulk nanocrystalline ceramics, and may revolutionize the design of ceramic armor.

"NRL was the first to see the increase of energy dissipation in single digit nano-grain ceramics," said Dr. Boris Feygelson, a materials research engineer in NRL's Electronics Science and Technology Division, leading the team's efforts in nanosintering. "The better the material can accommodate mechanical energy, the better it can stop an incoming threat."

The key to unlocking these materials and their phenomenon is NRL's unique approach to forming large-scale nanostructured solids. The unparalleled nanosintering approach is called Environmentally Controlled Pressure Assisted Sintering, or EC-PAS. It allowed NRL to break the world record for the smallest grain size in dense ceramics at 3.6 nanometers, which is about 30,000 times smaller than the width of a human hair.

"What we've done is develop a new way to make nanocrystalline materials and demonstrated that by varying the nano-grain size there is the capability to design a ceramic with specific combinations of properties," said Feygelson.

By pushing the boundaries of nanosintering science, NRL researchers showed that it may be possible to one day design a lightweight, nanocrystalline ceramic material that can better dissipate mechanical energy, say from a sharp projectile, absorbing more damage while retaining its very high hardness. This discovery could pave the way for more efficient armor for Sailors and Marines.

"In general, the Navy wants to lighten the load of the warfighter," said Wollmershauser. "If you can make harder armor, or better performing armor, then you can put less armor on a person or vehicle, in turn increasing capacity for other things like munitions and electronics."

Behind the collaborative effort were individuals from three divisions across NRL, including chemistry, materials science and technology, and electronics science and technology.

"We are fortunate to have a team from three different divisions," said Ryou. "The diverse expertise of our team members allowed this work to happen."

The team hopes to continue their work in bulk nanocrystalline ceramics, the development of the EC-PAS nanosintering technique being the key to future innovation.

"When we were doing this research we started to develop a vision for other applications. We realized that we could approach this research in nanocrystalline materials with a much broader perspective," said Feygelson. "EC-PAS opens the door to explore limits of many phenomena in nanostructured materials. Armor materials is just the beginning. So, suffice it to say... stay tuned."

The team's research was recently published in American Chemical Society Nano and can be found at the following link, http://pubs.acs.org/doi/10.1021/acsnano.7b07380 .

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