Applications of silicon carbide, boron carbide and other advanced ceramics in bulletproof fields
Applications of silicon carbide, boron carbide and other advanced ceramics in bulletproof fields
Ordinary ceramics are brittle. Depending on modern science and technology, they become the advanced ceramics which have good hardness and high-strength. The advanced ceramics should be the new material in bulletproof field with special physical performance requirements. Thus, the ceramics have become a very popular bulletproof material.
01 Bulletproof principle of ceramic materials
The bulletproof is used for consuming projectile energy and slowing down projectile speed in order to minimize the harms on the bulletproof users. Most traditional engineering materials, such as metal and so on, absorb energy through plastic deformation of structure, while ceramic materials absorb energy by micro crushing process.
There are three stages in the energy absorption process of bulletprrof ceramics roughly:
1) Initial impact stage
When the projectile hits ceramic surface of bulletproof, the warhead will become blunt. During the process of crushing the ceramic surface, the energy will be absorbed. It will cause 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. Then, the back plate will be deformed. The remaining energy will be absorbed by deformation of the back plate material. In the process of projectile impacting ceramic, both projectile and ceramic are damaged.
02 Requirements of bulletproof ceramics on material properties
Due to the ceramic’s brittleness, it will fracture rather than plastic deformation while being 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, bulletproof 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. |
03 The most commonly used bulletproof ceramic materials
Since the 21st century, bulletproof ceramics have been developed rapidly. The various types of bulletproof ceramics include 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 popular in the world.
The density of alumina ceramics is the highest. However, its hardness is relatively low. With low level processing threshold, the price of alumina ceramics is also low. According to the purity of alumina, alumina ceramics are divided into 85/90/95/99. 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 |
Properties comparison of materials
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. Meanwhile, they also have high requirements for processing technology, requiring high-temperature and high-pressure sintering. Therefore, cost of Boron carbide ceramics should be highest among three kinds of ceramics.
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Compared with these three common bulletproof ceramic materials, alumina bulletproof ceramics has lowest cost. However, 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 produced in domestic market. However, single crystal alumina can be used to prepare transparent ceramics, which is widely used as optical functional transparent materials.Single crystal alumina is also applied to military equipment such as individual bulletproof masks, missile detection windows, vehicle observation windows, submarine periscopes, etc.
04 Two most popular bulletproof ceramic materials: Silicon carbide bulletproof ceramics
Depending on extremely strong covalent bond, silicon carbide still has high strength bonding at high temperatures. This structural feature gives silicon carbide ceramics good properties, which include excellent strength, high hardness, wear resistance, corrosion resistance, high thermal conductivity, good thermal shock resistance and others. Meanwhile, silicon carbide ceramic is one of the most promising high-performance armor protection materials, which has moderate price and high cost performance.
Silicon carbide ceramics have been regarded as the protective armor material. They have broad development space in the field of armor protection. Their applications in the fields of individual equipment and special vehicles tend to be diversified. 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. They 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. Its hardness is up to 3000 kg/mm². It has low level density of 2.52g/cm³ which is 1/3 of steel. It has high elastic modulus (450 GPa) and high melting point (about 2447 ℃), as well as high thermal conductivity. However, its thermal expansion coefficient is low. In addition, boron carbide has good chemical stability, acid resistance, alkali resistance and corrosion resistance. At room temperature, boron carbide does not react with acids, bases and most inorganic compound liquids. Boron carbide has slow corrosion only in the mixture of hydrofluoric acid sulfuric acid and hydrofluoric acid nitric acid. At the same time, boron carbide does not wet and interact 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. In addition, its high elastic modulus makes it a good choice for military armor and space materials. The main problem with B4C is that it is expensive (about 10 times that of alumina). The brittleness of the product limits its wide application as single-phase protective armor.
05 Preparation method of bulletproof ceramics
Based on the characteristics of ceramic material preparation process, SiSiC, SSiC and liquid phase sintering are relatively mature in the current process development. The three sintering methods have low production cost, simple preparation process and high possibility of mass production. Due to the limitation of product size, hot pressing sintering and hot isostatic pressing sintering have high production cost and low maturity. Ultra high pressure sintering, microwave sintering, spark plasma sintering and plasma beam melting are relatively new preparation methods with the lowest maturity. Due to the high requirements for technology and equipment, their production costs are high, which leads to low feasibility of mass production. They are often used in the experimental exploration stage and have little significance for practical application. Therefore, it is difficult for them to realize industrialization.
06 Upgrade of bulletproof ceramics
Silicon carbide and boron carbide have great bulletproof potential. However, poor fracture toughness and brittleness of single-phase ceramics can not be ignored. With the development of modern science and technology, the functionality and economy of bulletproof ceramics are highlighted, which is presented as multi-function, high performance, light weight, low cost and safety. Recently, 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. However, this armor is lighter than current armor, which improves the mobility of combat troops.
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. With the development of sintering technology, the advantages of boron carbide ceramics are more and more outstanding.
Post time: Dec-03-2022