Harder Ceramic Armor

Boron carbide has already seen plenty of action as a material for body armor. But limitations in this ceramic's density and ability to tolerate complex shapes, have restricted it to small, flat, armor inserts. Verco Materials LLC has now developed a way to render this useful material 100 percent dense and amenable to more complex geometries.

One key to the company's breakthrough is a carefully controlled sintering process. "Boron carbide historically hasn't sintered well," says Robert Speyer, an engineering professor at the Georgia Institute of Technology and Verco's CEO. And these sintering problems have limited the density of commercially-available boron carbide to about 98 percent after a secondary hot pressing step, according to Speyer.

	More density means more hardness

Even this small amount of porosity has limited the material's utility in armor applications. "Porosity severely degrades the ballistic properties of ceramic armor by acting as a crack initiator," Speyer explains, adding that density goes hand in hand with hardness. What's more, the hot pressing step required the parts to be stacked together in a nesting arrangement, which limited pressed boron carbide parts to mostly flat geometries.

Verco's technology, which takes its cues from Speyer's academic research, addresses both the sintering and pressing steps. The company has developed a pressureless sintering method that, by itself, achieves densities (about 98 percent) comparable to those of traditional pressed boron carbide parts. Verco then runs the parts through a post-sintering Hot Isostatic Pressing (HIP) operation that brings the density up to 100 percent.

And this additional density has important engineering consequences. "Density scales with hardness," Speyer says (see chart).

The process, meanwhile, doesn't require the multiple-part stacks, so it allows more design freedom. Verco has created some parts with real depth, including a quarter-scale prototype helmet under a research contract with the military. The company has also produced powder-injection-molded parts that have even more features and complexity. To take one example, the company has molded, sintered and HIPed a 1.5-cm atomizer nozzle with molded-in threads.

In terms of applications, Verco's initial focus has been on prototype projects for the military. Yet even more opportunities exist for commercial parts. Beth Judson, Verco's general manager, reports that wear-resistant nozzles are a promising area for the new technology. "In this case, we would be a harder, more wear-resistant alternative to cemented carbide," she says. Verco is also looking at some automotive applications that now rely on coated metals. She gives valve retainers as an example. Finally, the company is also evaluating the material for silicon nitride bearings. "Boron carbide is again a harder alternative," she says.