For the ballistic protection of aircraft, especially for helicopters, as well as for land vehicles and personal armour, lightweight protection systems are required. State of the art ceramic armour systems (Al2O3, SiC, B4C) are characterized by a significantly lower area weight compared to metallic armour based on hardened steel or aluminum. The main disadvantage of these monolithic ceramics is their high brittleness, leading to insufficient multiple hit performance. Additionally, the manufacturing costs are high, due to the use of very fine ceramic powders as well as due to high process temperatures, needed for hot isostatic pressing, sintering or liquid phase sintering.
In a new approach, biomorphic SiSiC ceramics were developed on the basis of low cost wooden preforms and the LSI process (liquid silicon infiltration. In first ballistic tests using armour piercing ammunition (e.g. 7.62 x 51 AP with steel core) high protection performance could be obtained, comparable to conventional SiC ceramics. Due to the use of low cost raw materials and near neat shape manufacturing methods,based on LSI and in situ joining technology, biomorphic SiSiC materials offer both technical and economic advantages compared to conventional SiC ceramics, especially regarding the manufacture of complex shaped, large sized components (e.g. helicopter seats).
In order to increase the multiple hit performance, large sized biomorphic SiSiC structures with integrated crack stoppers have been developed. Therefore MDF (medium density fiberboard) preforms are pyrolized (900 °C, N2) in a first step. In the next step a defined slit system is cut into the resulting, porous carbon preform via jet cutting. In the last step, the carbon preform is infiltrated with melted silicon (1650 °C, vacuum), reacting almost completely with the carbon preform forming SiC. Remaining porosity is filled with silicon and a dense SiSiC material is obtained. The slits remain open during siliconization, leading to a large-sized panel, consisting of a multitude of small individual tiles, however connected by tiny bars. Thereby impact damage can be limited to individual tiles. Compared to the common „mosaic design “, where many single tiles have to be glued on a support structure in a time consuming and costly procedure, large sized protection systems, especially with curved shapes, can be build up easily using this new technology.
Current development focuses on: