Dec 8 2005
A Georgia Institute of Technology researcher has developed a process that increases the hardness and improves the ballistic performance of the material used by the U.S. military for body armor. The researcher’s start-up company is commercializing the technology.
Boron carbide is the Defense Department’s material of choice for body armor. It is the third hardest material on earth, yet it’s extremely lightweight. But it has an Achilles heel that piqued the interest of Georgia Tech Professor of Materials Science and Engineering Robert Speyer five years ago.
He knew that the boron carbide powder used to form the armor had a reputation for poor performance during sintering—a high-temperature process in which particles consolidate, without melting, to eliminate pores between them in the solid state. Poor sintering yields a more porous material that fractures more easily – not a good thing for a soldier depending on it to stop a bullet.
Determined to understand the sintering problem, Speyer built an instrument called a differential dilatometer to measure the expansion and contraction of materials during sintering heat treatments to temperatures as high as 4,300 degrees Fahrenheit.
“As a particle compact sinters, it shrinks 12 to 15 percent,” Speyer explained. “There are nuances that occur in contraction, and if you monitor them accurately (with a dilatometer), it tells you what is happening at different stages in the sintering process. So we used that information in conjunction with additional materials characterization techniques to figure out the reasons why boron carbide didn’t sinter well, and then found ways around them.”
From these findings, Speyer and his research team have created a new boron carbide formation process based on methodical control of thermal and atmospheric conditions during sintering. The method yields higher relative densities – and thus better ballistic performance – than currently available boron carbide armor. (Relative density is a percentage that indicates how close a material is to its theoretical density, which implies having no pores.)
The research has been reported in the Journal of Materials Research.
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