Application of SIC and B4C ceramics in the field of bulletproof armor

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As a key member of non-metallic materials, ceramic materials have a large number of attractive properties, such as good mechanical and electrochemical properties, low thermal conductivity, compact and uniform structure, wear and corrosion resistance, and so on. The high specific stiffness, high specific strength and chemical inertness of ceramic materials in complex environments, and the low density, high hardness and high compressive strength of metal materials, make it very promising in the application of armored systems. And has been widely used in body armor, vehicles and aircraft and other equipment in the protective armor.

1. The bulletproof principle of ceramic materials

Metal materials can absorb the energy of the bullet through plastic deformation, and ceramics, as a brittle material, the plastic deformation is almost zero when it is broken. Therefore, under the action of the large impact force of the warhead, the ceramic material mainly absorbs energy through the micro-fragmentation process. The main process is roughly divided into three stages: the initial impact stage, the erosion stage and the deformation fracture stage. The armored ceramic surface layer can passivate the warhead, and the surface will be crushed into small and hard particles. When the blunt projectile continues to deepen, the armored ceramic will form a fragment layer. The tensile stress inside the material will cause the ceramic to break, and the remaining energy will be absorbed by the back plate. . The ability of ceramics to absorb energy is related to the hardness and elastic modulus of the ceramics. Generally, ballistic quality factors are used to comprehensively measure the anti-elastic properties of ceramics:

(In the formula: E is the modulus of elasticity, H is the hardness, and ρ is the density.)

It can be seen that the greater the elastic modulus and hardness of the ceramic, the lower the density, the stronger the ceramic’s ability to absorb kinetic energy, that is, the better the ballistic performance.

2. Gemini of bulletproof armor material

In short, the high hardness of the ceramic material enables it to passivate or even break the warhead, and absorb the energy of the high-speed warhead through its own crushing process; at the same time, the ceramic material has less than half the density of steel, which is very suitable for mobile armor and individual soldiers. Protection.

Silicon carbide and boron carbide ceramics have been used in the field of bulletproof armor for a long time. In the 1960s, boron carbide ceramics were first used in the design of bulletproof vests and assembled on the seats of airplane pilots. Afterwards, a bulletproof ceramic composite armor composed of a ceramic panel and a composite back plate.

Boron carbide is a strong covalent bond compound, with a covalent bond as high as 93.9%, so it has the characteristics of low density, high strength, high temperature stability and good chemical stability. The product is especially suitable for the application of lightweight armor. At the same time, compared with diamond and cubic boron nitride, boron carbide is easy to manufacture and low in cost. Like boron carbide, silicon carbide has extremely strong covalent bonds and high-strength bonding at high temperatures. This structural feature gives silicon carbide ceramics excellent strength, hardness, and wear resistance.

As a bulletproof material, the above-mentioned materials are prepared into powder and sintered into a block to become a ballistic-proof ceramic block, which is then further integrated with other ingredients to become a finished product that can be equipped.

As shown in the above figure, we found that both silicon carbide and boron carbide ceramics have the characteristics of low density. The density of common alumina ceramics is about 3.5g/cm-3, while the density of silicon carbide and boron carbide are only 3.2g/cm-3. And 2.5g/cm-3. It can be seen that under the trend of lightweight mobile armor, silicon carbide and boron carbide materials have inherent advantages.

1) In terms of elastic modulus, the elastic modulus of alumina ceramics is about 350GPa, while the elastic modulus of silicon carbide and boron carbide materials is about 400GPa. The elastic modulus of silicon carbide ceramics made by reaction sintering by the Shanghai Institute of Ceramics It can reach between 360-380GPa, while the elastic modulus of silicon carbide sintered by the same reaction in the United Kingdom and the United States can reach more than 430GPa. It can be seen that the three main armor ceramic materials all have the characteristics of high elastic modulus.

2) In terms of hardness, boron carbide>silicon carbide>alumina. It is worth mentioning that, as the key material for the production of cemented carbide, tungsten carbide material, compared with silicon carbide, the hardness of silicon carbide is twice that of tungsten carbide, the density is 1/5 of tungsten carbide, and the strength is maintained at 1400 ℃ Does not fall.

3) In terms of wear resistance, boron carbide>silicon carbide>alumina. Data measured by the Institute of Powder Metallurgy of Central South University show that the wear resistance of alumina ceramics is equivalent to 266 times that of manganese steel and 171.5 times that of high-chromium cast iron. It can be seen that the high hardness and high wear resistance of ceramic materials are much higher than wear-resistant steel and stainless steel.

4) In terms of other properties, boron carbide is unique in high-temperature thermal stability. Compared with alumina, its thermal expansion coefficient is less than 1/2. At 500℃, its thermal conductivity is one order of magnitude higher, and its thermal shock resistance is nearly 20 times higher. However, it has poor fracture toughness, low tensile strength, and is prone to brittle fracture. The ceramic composite target plate must be bonded by the ceramic face plate and the composite material back plate to overcome the failure of the ceramic due to the tensile stress. This kind of composite target plate is usually made by bonding small pieces of ceramic panels and composite material backing plates, which can also prevent the whole ceramic panel from breaking. When the projectile invades, only a single piece of armor will be crushed.

With the development of lightweight and high-efficiency armor systems, the superiority of bulletproof ceramics has become more prominent. As the twin stars of bulletproof armor materials, silicon carbide and boron carbide materials, it is believed that there is still much room for improvement.