APPLICATION OF SILICON CARBIDE, BORON CARBIDE AND OTHER ADVANCED CERAMICS IN BULLETPROOF FIELD
Ordinary ceramics are fragile. However, the advanced ceramics processed by modern science and technology have become a hard and high-strength new material, especially in the bulletproof field with special physical performance requirements for materials. Ceramics have become a very popular bulletproof material.
01 Bullet proof principle of ceramic materials
The basic principle of armor protection is to consume projectile energy, slow down projectile and make it harmless. Most of the traditional engineering materials, such as metal materials, absorb energy through plastic deformation of the structure, while ceramic materials absorb energy through micro crushing process.
The energy absorption process of bulletproof ceramics can be roughly divided into three stages:
(1) Initial impact stage: the projectile hits the ceramic surface, making the warhead blunt, and absorbing energy in the process of crushing the ceramic surface to form a small and hard fragment area;
(2) Erosion stage: the blunt projectile continues to erode the fragment area, forming a continuous ceramic fragment layer;
(3) Deformation, crack and fracture stages: finally, tensile stress is generated in the ceramic to break the ceramic, and then the back plate is deformed. The remaining energy is absorbed by the deformation of the back plate material. In the process of the projectile impacting the ceramic, both the projectile and the ceramic are damaged.
02 Requirements of bulletproof ceramics on material properties
Because of the brittleness of the ceramic itself, it will fracture rather than plastic deformation when impacted by the projectile. Under tensile load, fracture first occurs in heterogeneous places such as pores and grain boundaries. Therefore, in order to minimize the micro stress concentration, armored ceramics should be high-quality ceramics with low porosity (up to 99% of the theoretical density) and fine grain structure.
Material Performance and Its Influence on Bullet proof Performance.
|
Performance |
Impact on bulletproof performance |
|
Density |
Mass of armor system |
|
Hardness |
Extent of destruction of projectiles |
|
Elastic modulus |
Stress wave transmission |
|
Strength |
Anti multiple strike performance |
|
Fracture mode |
Anti multiple strike performance |
|
Fracture toughness (intercrystalline or transgranular) |
Ability to absorb energy |
|
Microstructure |
Grain size, second phase, phase transformation or amorphization, porosity, etc. affect all properties. |
03The most commonly used bulletproof ceramic materials
Since the 21st century, bulletproof ceramics have developed rapidly with many kinds, including aluminum oxide, silicon carbide, boron carbide, silicon nitride, titanium boride, etc. Among them, aluminum oxide ceramics (Al2O3), silicon carbide ceramics (SiC), and boron carbide ceramics (B4C) are the most widely used.
The density of alumina ceramics is the highest, but the hardness is relatively low, the processing threshold is low, and the price is low. According to the purity, alumina ceramics are divided into 85/90/95/99, and the corresponding hardness and price are also increased in turn.
|
Material |
Density Kg/m3 |
Elastic modulus GN/m2 |
HV |
Price relative to alumina |
|
Boron carbide |
2500 |
400 |
30000 |
x 10 |
|
Alumina |
3800 |
340 |
15000 |
1 |
|
Titanium diboride |
4500 |
570 |
33000 |
x 10 |
|
Silicon carbide |
3200 |
370 |
27000 |
x 5 |
| Beryllium oxide |
2800 |
415 |
12000 |
x 10 |
| B4C/SiC |
2600 |
340 |
27500 |
x 7 |
| Glassware and Ceramics |
2500 |
100 |
6000 |
1 |
| Silicon nitride |
3200 |
310 |
17000 |
x 5 |
Comparison of material properties
Silicon carbide ceramics are structural ceramics with relatively low density and high hardness, which are cost-effective. Therefore, they are also the most widely used bulletproof ceramics in China.
Boron carbide ceramics have the lowest density and the highest hardness among these kinds of ceramics, but at the same time, they also have high requirements for processing technology, requiring high-temperature and high-pressure sintering, so the cost is also the highest among the three kinds of ceramics.
Compared with these three common bulletproof ceramic materials, the cost of alumina bulletproof ceramics is the lowest, but its bulletproof performance is far inferior to that of silicon carbide and boron carbide. Therefore, at present, silicon carbide and boron carbide bulletproof ceramics are mostly produced in domestic bulletproof ceramic manufacturers, while alumina ceramics are rare. However, single crystal alumina can be used to prepare transparent ceramics, which is widely used as optical functional transparent materials, and is applied to military equipment such as individual bulletproof masks, missile detection windows, vehicle observation windows, submarine periscopes, etc.
04The two most popular bulletproof ceramic materials
Silicon carbide bulletproof ceramics
The covalent bond of silicon carbide is extremely strong, and it still 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; At the same time, silicon carbide ceramic is one of the most promising high-performance armor protection materials with moderate price and high cost performance.
Silicon carbide ceramics have broad development space in the field of armor protection, and their applications in the fields of individual equipment and special vehicles tend to be diversified. As a protective armor material, considering the cost, special application and other factors, small ceramic panels and composite backplates are usually bonded to form ceramic composite targets to overcome the failure of ceramics due to tensile stress, and ensure that only single pieces are crushed without damaging the entire armor when the projectile penetrates.
Boron carbide bulletproof ceramics
At present, boron carbide is a super hard material whose hardness is only inferior to diamond and cubic boron nitride, and the hardness is up to 3000 kg/mm ²； Low density, only 2.52g/cm ³， 1/3 of steel; High elastic modulus, 450GPa; High melting point, about 2447 ℃; Its thermal expansion coefficient is low and its thermal conductivity is high. In addition, boron carbide has good chemical stability and is resistant to acid and alkali corrosion. It does not react with acid and alkali and most inorganic compound liquids at room temperature. It only has slow corrosion in hydrofluoric acid sulfuric acid and hydrofluoric acid nitric acid mixtures; It is not wetted and interacts with most molten metals. Boron carbide also has a good ability to absorb neutrons, which other ceramic materials do not have. The density of B4C is the lowest among several commonly used armor ceramics, and its high elastic modulus makes it a good choice for military armor and space materials. The main problems of B4C are its high price (about 10 times that of alumina) and high brittleness, which limit its wide application as single-phase protective armor.
05 Preparation method of bulletproof ceramics
It can be seen from the characteristics of the preparation process of ceramic materials that reaction sintering, pressureless sintering and liquid phase sintering are relatively mature in the current process development. The production costs of these three sintering methods are low, the preparation process is simple, and the possibility of mass production is high. Hot pressing sintering and hot isostatic pressing sintering are relatively limited by product size, with high production cost and low maturity. Ultrahigh pressure sintering, microwave sintering, spark plasma sintering and plasma beam melting are relatively new preparation methods with the lowest maturity. However, they have high requirements for technology and equipment, high production costs, and low feasibility of batch production. They are often used in the experimental exploration stage, which is of little significance for practical applications and difficult to achieve industrialization.
06 Upgrade of bulletproof ceramics
Although silicon carbide and boron carbide have great bulletproof potential, the problems of poor fracture toughness and brittleness of single-phase ceramics can not be ignored. The development of modern science and technology requires the functionality and economy of bulletproof ceramics: multi-function, high performance, light weight, low cost and safety. Therefore, in recent years, experts and scholars hope to strengthen, toughen, lighten and economize ceramics through micro adjustment, including composite of multiple ceramic systems, functional gradient ceramics, layered structure design, etc., and such armor is lighter than today's armor, which better improves the mobility of combat units.
Functional gradient ceramics are characterized by regular changes in the properties of component materials through micro design. For example, titanium boride and metal titanium as well as aluminum oxide, silicon carbide, boron carbide, silicon nitride and metal aluminum and other metal/ceramic composite systems have a gradient change in performance along the thickness, that is, to prepare bulletproof ceramics that transition from high hardness to high toughness.
Nanocomposite ceramics are composed of submicron or nanometer dispersed particles added to the matrix ceramics. For example, SiC-Si3N4-Al2O3, B4C-SiC, etc. can improve the hardness, toughness and strength of ceramics. It is reported that the western countries are studying how to prepare ceramics with grain size of tens of nanometers by sintering nanoscale powders, so as to strengthen and toughen the materials. Ballistic ceramics are expected to achieve a major breakthrough in this regard.
07 Summary
Whether it is single-phase ceramics or multiphase ceramics, the best bulletproof ceramic materials are still inseparable from silicon carbide and boron carbide. Especially boron carbide materials, with the development of sintering technology, the advantages of boron carbide ceramics are more and more outstanding, and their applications in the bulletproof field will be further developed.