Properties and core production technology of silicon carbide bulletproof ceramics

 

Silicon carbide bulletproof ceramics

 

The common bulletproof layer of body armor is usually composed of polyethylene plate and ceramic insert plate, of which ceramic insert plate mainly has two kinds: mosaic small ceramic bulletproof plate and whole bulletproof plate. At present, the bullet-proof ceramics has different types: alumina, zirconia, silicon carbide, boron carbide, aluminum nitride, silicon nitride, titanium boride and so on. Among them, silicon carbide ceramics is a bulletproof material which has been studied more at home and abroad in recent years.

Silicon carbide is made of Si-C tetrahedron accumulation, α and β two crystal types. At the sintering temperature below 1600℃, SiC exists in the form of β-sic, when the sintering temperature is higher than 1600℃, β-sic slowly transformed into α-sic. Alpha silicon carbide covalent bond is very strong, ans has high strength bonding at high temperatures. This structural feature gives silicon carbide ceramics excellent strength, high hardness, wear resistance, corrosion resistance, high thermal conductivity, good thermal shock resistance and other properties. Since silicon carbide ceramics price is moderate, cost-effective, it is considered to have the potential for development of high-performance bulletproof materials.
 

The common molding methods of silicon carbide ceramics are die-pressing, grouting, cold isostatic pressing, gel injection molding, etc.
 

1. Die-pressing: die-pressing is the current silicon carbide bulletproof sheet commonly used molding method. Its process is simple, easy to operate, has high production efficiency, and is conducive to continuous production.
 

2. Grouting molding: grouting molding has strong adaptability, can get a variety of shapes, structures of the bad body. It has obvious advantages in the preparation of silicon carbide ceramic shaped parts.
 

3. Cold isostatic pressing: the blank body obtained by cold isostatic pressing has uniform force and uniform density distribution, and the product performance has been greatly improved, which is suitable for high-performance silicon carbide ceramics production. 
 

4. Gel injection molding: Gel injection molding technology is a new type of near-net size molding method. The green body has uniform structure and high strength, which can carry out various mechanical processing on the bad body and reduce the processing cost after sintering. It is suitable for silicon carbide ceramics with complex structure.
 

In addition to molding, sintering is also the core process of silicon carbide ceramic production. At present, the sintering process of SIC ceramics includes reaction sintering, hot pressing sintering, hot isostatic pressing sintering and non-pressing sintering.
 

1. Reaction sintering: Reaction sintering is a near-net size manufacturing technology. Its process is simple, low cost, and can be achieved in the low temperature of 1450~1600℃ in a short time through the siliconizing reaction sintering of silicon carbide. Reaction sintering can prepare large size, complex shape parts. However, due to the inherent defects of siliconizing reaction sintering, it is inevitable that there is 8% to 12% free silicon in silicon carbide, which reduces the high temperature mechanical properties, corrosion resistance and oxidation resistance of the material, and the use temperature is also limited, which usually cannot exceed 1350℃.
 

2. Hot press sintering: Hot press sintering is a sintering method that fills dry silicon carbide powder into the model, pressurizes and heats it from a single axis direction, so that the molding and sintering are completed at the same time. Because the heating and pressurization are carried out at the same time, it is helpful to the contact diffusion of particles and the flow mass transfer process, which can reduce the sintering temperature and shorten the sintering time, and obtain silicon carbide ceramic products with fine grains, high relative density, and good mechanical properties. The disadvantage of hot-pressing sintering is that the process is more complex, the mold material and equipment requirements are high, the production efficiency is low, the production cost is high, and can only make products of simple shapes.
 

3. Hot isostatic pressing sintering: Hot isostatic pressing sintering refers to the process of sintering densification of silicon carbide ceramic powder, green body, or pre-fired body through the joint action of high temperature and isotropic high-pressure gas. Hot isostatic pressing sintering can improve the performance of SIC ceramics, but because of the complex process and high cost, it has not been put into large-scale production.
 

4. Non-pressure sintering: non-pressure sintering silicon carbide ceramics has high temperature performance. The sintering process is simple and low cost, suitable for more forming methods, and can be used for complex shape and thick large parts, but the method is also suitable for mass industrial production, which has become an important method for the preparation of silicon carbide ceramics.
 

Multi-curved silicon carbide bulletproof plate

Kingcera special porcelain has complete forming, sintering equipment, and mature silicon carbide ceramic non-pressure sintering technology. The produced silicon carbide ceramic bulletproof sheet has shown excellent performance and stable quality and has been well received since it was put into the market.