Just add silicon: Engineers develop recipe to strengthen body armor

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Researchers at Texas A&M University have formulated a new recipe that can prevent weaknesses in modern-day armor. By adding a tiny amount of the element silicon to boron carbide, a material commonly used for making body armor, they discovered that bullet-resistant gear could be made substantially more resilient to high-speed impacts.

“For the past 12 years, researchers have been looking for ways to reduce the damage caused by the impact of high-speed bullets on armor made with boron carbide,” said Kelvin Xie, assistant professor in the Department of Materials Science and Engineering. “Our work finally addresses this unmet need and is a step forward in designing superior body armor that will safeguard against even more powerful firearms during combat.”

Boron carbide, dubbed “black diamond,” is a man-made material, which ranks second below another synthetic material called cubic boron nitride for hardness. Unlike cubic boron nitride, however, boron carbide is easier to produce on a large scale. Also, boron carbide is harder and lighter than other armor materials like silicon carbide, making it an ideal choice for protective gear, particularly ballistic vests.

Despite boron carbide’s many desirable qualities, its main shortfall is that it can damage very quickly upon high-velocity impact.

Previous work using computer simulations predicted that adding a small quantity of another element, such as silicon, had the potential to make boron carbide less brittle. Xie and his group investigated if adding a tiny quantity of silicon also reduced phase transformation.

To simulate the initial impact of a high-speed bullet, the researchers made well-controlled dents on boron carbide samples with a diamond tip, whose width is smaller than a human hair. Then, under a high-powered electron microscope, they looked at the microscopic damage that was formed from the blows.

Xie and his collaborators found that even with tiny quantities of silicon, the extent of phase transformation went down by 30 percent, noticeably reducing the damage from the indentation.

Although silicon serves well to enhance boron carbide’s properties, Xie said, more experiments need to be done to know if other elements, like lithium and aluminum, could also improve boron carbide’s performance.

This study was partly sponsored by the Defense Advanced Research Projects Agency (DARPA).

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