Non-oxide, high-performance technical ceramics that are formed simultaneously under high pressure and temperature have been shown to achieve high mass efficiencies (i.e., significant weight savings) compared to armor metals and sintered ceramics against a variety of threats due to their low density, high hardness and high elastic modulus.
Hot pressed boron carbide (typically B4C) is used for personnel protection in the form of plate inserts, for aircraft protection as panels and seats, in ships, and in armored land vehicles as seats. For protection against more lethal threats, such as heavy machine gun and medium cannon threats, hot-pressed silicon carbide (SiC) is typically the material of choice. Hot pressed silicon carbide is also used in armored vehicles as an applique, along with hot-pressed silicon nitride (Si3N4). (Titanium diboride [TiB2], while as effective ballistically, is not as widely used for ceramic armor, primarily for the lack of alternative market applications.)
Regardless of the ceramic material used, ceramic armor is damaged on impact, and this damage propagation affects the subsequent ceramic performance. Extensive research has shown that this damage is caused by the activation of preexisting defects by the shear and tensile forces that are generated on impact. The resulting behavior of the ceramic is a complicated combination of the integrated responses of the damaged and undamaged regions. Since a ceramic is rarely, if ever, used as a stand-alone armor, the mechanical response of the entire system determines the degree to which the damage is generated and how well the damage is confined so that the armor continues to be effective against subsequent impacts.
While obvious system design improvements have been achieved over the last decade, extensive work on improving the properties of the ceramic materials continues. One of the most desired variables to eliminate is porosity, so that full theoretical densities are achieved. Hot pressing creates fully dense ceramics, so the focus on ceramics processed using this technique is on the other property improvements.
The best way to increase ceramic efficiencies is to extend the time that the ceramic works on a bullet to cause shattering; increase the dwell duration or dwell penetration transition velocity (the velocity above which penetration occurs, and below which the bullet is defeated on the ceramic surface); and/or achieve a greater pressure on the penetrator during penetration to increase the erosion efficiency of the highly damaged, comminuted ceramic. Additionally, and of particular interest in personnel armor protection, is a requirement to predictably defeat multiple impacts within a single plate or array.
Finally, cost, manufacturability and integration with the backing materials of the armor system must also be taken into consideration.