Characterisation, significance and detection of manufacturing defects in Reaction Sintered Silicon Carbide armour materials

Ceramics with high hardness values (>10 GPa), high elastic modulii (>300 GPa) and good flexural strength values (>350 MPa) make excellent armour materials. However, they are normally very expensive (>$10/kg) and difficult to shape. So, tiles of regular geometry (typically square or hexagonal) have been used in advanced armour systems, for military vehicles. However, for body armour applications, there is a need to form a monolithic ceramic into a double-curved, or even triple-curved, shape in order to better conform to the human torso. In a recent review, carried out by the Defence Materials Technology Centre of Australia, of the shaping techniques used for body armour components, uniaxial pressing of breastplates was still recognised to be the most feasible, and commercially available, process even though other techniques like Viscous Plastic Processing (VPP) were becoming established. One particular variant of the dry-pressing route is known as Reaction Sintering, or Reaction Bonding, in which a pre-pressed, dry powder compact is infiltrated, at elevated temperature, with a liquid metal. However, the process is prone to the formation of a range of manufacturing defects, some of which are extremely deleterious to impact behaviour and ballistic performance of the finished product. The origin, cause and effect of these defects are discussed in this paper, together with both current and future NDI techniques.