Researchers receive $2 million DARPA grant for fracture resistant ceramics

Washington State University researchers have received a $2 million grant to develop tough-to-shatter ceramic materials.

Funded by U.S. Department of Defense's Defense Advanced Research Projects Agency (DARPA), the researchers aim to add small amounts of aluminum to a ceramic material known as boron carbide and use forging to manufacture ceramics that resist shattering. The project is led by Arezoo Zare, assistant professor in WSU's School of Mechanical and Materials Engineering.

Ceramics have excellent mechanical properties - they're harder, stronger, and lighter than steel and most common alloys used in industry. Boron carbide is an advanced ceramic and one of the hardest materials known. It is also very light - only two and a half times as dense as water.

"The combination of high strength and light weight makes boron carbide desirable for applications as structural components in airplane, spacecrafts, and automobiles," said Zare.

However, while ceramics generally outperform metal alloys in strength, their widespread use has been hindered because they're brittle - they can easily shatter under external forces.

"Researchers have been trying to resolve this issue for a long time through different approaches," said Zare. "There have been improvements which expanded the use of ceramics in recent years, but ceramics are still inferior to metals in fracture resistance. Unless we can resolve that issue, there's always this concern - this material may be very strong, but what if it just suddenly fails."

While ceramics generally outperform metal alloys in strength, their widespread use has been hindered because they're brittle - they can easily shatter under external forces.

Interestingly, their perfection at the atomic scale is why ceramics shatter.

When metal is deformed under external forces, the regular arrangement of atoms is disturbed, creating atomic scale defects, called dislocations - similar to a slipped thread in a woven fabric. The dislocations allow metals to be malleable.

"That's why we can use aluminum to make a window frame or a thin sheet of foil without fracture,'' said Zare.

Ceramics have a much higher melting temperature than most metals. To fabricate them, the ceramic material is ground into a fine powder and then the powder is pressed into shapes and baked in a furnace under pressure. Rather than melting, the powder particles fuse together into nearly perfect atomic layers. This means there are no atomic scale defects and therefore the resulting material is brittle.

For their project, the research team will be adding small amounts of aluminum to the boron carbide ceramic and using forging at high temperature to introduce atomic scale dislocations in the materials.

"This means we will essentially have an atomic structure that looks more similar to a typical metal," she said. "We expect to see mechanical properties similar to metal as well where the ceramic can deform without fracture."

Researchers have used this technique to improve ceramics at very small scales, but Zare's team is working to develop a scalable process that would allow industry to make the material quickly at a reasonable cost.

In addition to Zare, the team for the two-yearproject includes researchers from Lawrence Livermore National Laboratory, Iowa State University, and Johns Hopkins University.