The difference between silicon carbide and boron carbide

Since the beginning of this year, global conflicts such as the Russia Ukraine conflict and the Israeli Palestinian conflict have attracted widespread attention worldwide. In such a global environment, the national defense of various countries has gradually become tense, which has made the market for some military materials very hot recently. Among them, as the two giants in the bulletproof ceramic industry, silicon carbide and boron carbide will certainly not be absent.Do you know why ceramics are bulletproof? What are the performance requirements of bulletproof ceramics for materials? Let's explore it together.

What is the bulletproof principle of ceramic materials?

The basic principle of armor protection is to consume projectile energy, slow down the projectile, and achieve harmlessness. The vast majority of traditional engineering materials, such as metal materials, absorb energy through structural plastic deformation, while ceramic materials absorb energy through micro crushing processes. The energy absorption process of bulletproof ceramics can be roughly divided into three stages:
Initial impact stage:
The projectile impacts the ceramic surface, causing the warhead to become blunt and absorbing energy during the process of crushing and forming small and hard fragments on the ceramic surface;
Erosion stage:
The blunt projectile continues to erode the fragmented area, forming a continuous layer of ceramic fragments;
Deformation, cracking, and fracture stages:
Finally, tensile stress is generated in the ceramic, causing it to fracture. Subsequently, the back panel deforms, and all remaining energy is absorbed by the deformation of the back panel material. During the process of projectile impact on ceramics, both the projectile and the ceramics are damaged.

What are the requirements for material properties of bulletproof ceramics?

Due to the brittleness of ceramics themselves, they undergo fracture rather than plastic deformation when subjected to projectile impact. Under tensile loading, fracture first occurs in heterogeneous areas such as pores and grain boundaries. Therefore, in order to minimize micro stress concentration, armor ceramics should be high-quality ceramics with low porosity (up to 99% of the theoretical density value) and fine grain structure.
There are many types of bulletproof ceramic materials, including alumina, silicon carbide, boron carbide, silicon nitride, titanium boride, etc. Among them, alumina ceramic (Al2O3), silicon carbide ceramic (SiC), and boron carbide ceramic (B4C) are the most widely used. Aluminum oxide ceramics have the highest density, but relatively low hardness, lower processing threshold, and lower price. According to purity, they are divided into 85/90/95/99 aluminum oxide ceramics, and the corresponding hardness and price also increase sequentially.

Silicon carbide and boron carbide as raw materials for bulletproof materials?

Silicon carbide has a very strong covalent bond and still has a high-strength bond at high temperature. This structural feature endows silicon carbide ceramics with excellent properties such as strength, high hardness, wear resistance, corrosion resistance, high thermal conductivity and good thermal shock resistance. At the same time, silicon carbide ceramics are moderately priced and cost-effective, which is the most widely used bulletproof ceramics in China and one of the most promising high-performance armor protection materials. SiC ceramics have a 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 factors such as cost and special application, small ceramic panels and composite backboard are usually bonded to form a ceramic composite target to overcome the failure of ceramics caused by tensile stress, and to ensure that only a single piece is crushed without destroying the whole armor when the projectile penetrates.

Boron carbide is a superhard material whose hardness is second only to that of diamond and cubic boron nitride. Among these ceramics, the hardness is the highest and the density is the lowest, only 2.52g/cm3, which is 1/3 of that of steel. High elastic modulus, low thermal expansion coefficient and high thermal conductivity. In addition, boron carbide has good chemical stability, acid and alkali corrosion resistance, and does not react with acid and alkali and most inorganic compound liquids at room temperature; And is non-wetting and non-reactive with most molten metals. Boron carbide also has a good neutron absorption ability, which other ceramic materials do not have. B4C has the lowest density among several commonly used armor ceramics, and its high elastic modulus makes it a good choice for military armor and space materials. But at the same time, it also requires high processing technology, which requires high temperature and high pressure sintering, so the cost is the highest among the three ceramics (about 10 times that of alumina), which limits its wide application as a single-phase protective armor. Comparing these three kinds of common bulletproof ceramic materials, alumina bulletproof ceramic has the lowest cost, but its bulletproof performance is far worse than that of silicon carbide and boron carbide. Therefore, silicon carbide and boron carbide have become the two most popular bulletproof ceramic materials, which are mostly in domestic bulletproof ceramic production units, while alumina ceramics are rare. However, single crystal alumina can be used to prepare transparent ceramics, which is widely used as a transparent material with optical function, and is applied to military equipment such as individual bulletproof masks, missile detection windows, vehicle observation windows, submarine periscope and so on.

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