**3.6 Ceramics-based ballistic protection composites**

The constant race in armaments and the development of new types of weapons with different calibers, requires a response in protection from the same. Therefore, it is necessary to constantly develop ballistic materials that would protect people and vehicles on duty. Today, modern armies' function on the basis of three postulates: do not notice, do not shoot, and do not break through armor. The last, perhaps the most important requirement depends on the material. The efficiency of existing materials can be improved with ceramic-based composites.

The ceramic material can be reinforced by metal/metal oxide powder addition before sintering. This method of ceramic reinforcement was described by A.


**Table 6.**

*Physical, mechanical, and oxidation properties of TiB2.*

Pettersson et al. in the study of titanium-diboride reinforced by titanium powder addition before the sintering process [13]. The precursor powders were mixed in a high-speed planetary mil and after drying the matrix was treated by spark plasma sintering. The results of mechanical tests show that the composite with titanium contains between 5 and 6 wt. % have the best physical and mechanical properties. In the case of fracture toughness tests, this parameter is less sensitive to titanium content, except when 10% by weight is used, where toughness begins to increase rapidly. At the same procedure, ceramic composite can be reinforced by the addition of aluminum and magnesium [45], zirconia [46], and silicon [47].

Different reinforcement method of ceramics is the addition of ultra-high molecular weight polyethylene or low-density polyethylene (LDPE) before sintering by the hotpressing process to fill possible cavities (pores) formed during sintering. Oliveira et al. [48] had examined the ballistic properties of alumina-based composites reinforced by the different mass fractions of low-density polyethylene. In the stated examination, alumina-based composites were modified by 10–30 wt. % of low-density polyethylene. Results obtained by these tests lead to the following conclusions: LPDE has the function of keeping the alumina grains cohesive, LDPE among the alumina particles helps to increase the toughness of the composite and optimal addition of 20 wt. % of LDPE.

Ballistic ceramic-based composites can also be reinforced by a metal plate. The bonding of different materials by adhesion allows the composite to withstand the acoustic waves generated by the projectile impact. Due to the existence of acoustic impedance, in such composites, the effect of matching impedances produced by acoustic waves during projectile impact is reduced. Reducing this effect improves the physical and mechanical properties and prevents cracking of the ceramic armor, which allows one armor plate to protect itself from multiple impacts, provides structural integrity, and, to a lesser extent, the efficiency of the ballistic mass of the composite ceramic armor. Due to their increased mass, such composites are not used to increase the ballistic protection of people, but mainly vehicles. Due to the specific mass of metal and the load of the object, which requires an increase in ballistic protection, aluminum is most often used to strengthen ceramics-based composites. The main challenge in producing these composites is choosing the right adhesive. The adhesive must provide a ceramic-metal bond, not to allow easy separation of the composite during the impact of the projectile and to withstand the force of acoustic waves. The main criteria for choosing an adhesive is the ability to keep composites bonded after an impact of the projectile. The service life of the composite also depends on the quality of the adhesive. For this purpose, polymeric and high-temperature adhesives are used for ceramic-based composites production. One approach to improving the ballistic performance of ceramic armor with metal backings is to create a strong metallurgical bond and functionally graded composites in which metal layers transition to the ceramic layers without damaging interfaces. In ceramic-based composites, aluminum as backing material can be changed by other ceramics, Kevlar®, Twaron®, fiberglass, UHMWPE, and polyamide which can undergo thermal treatment of the glued ceramic product with backing material in an autoclave where temperature, pressure, and vacuum are applied.
