Introduction of bulletproof ceramic boron carbide
In the past forty or fifty years, with the development of science and technology, higher requirements have been put forward for materials in the technical fields of atomic energy, rockets, gas turbines, and so on. There is an urgent need for materials that are more resistant to high temperatures than heat resistant alloys and chemical corrosion than ordinary ceramics. Because some ceramics can meet these requirements, they have developed rapidly. These newly developed ceramics, which differ greatly from traditional ceramics in terms of raw materials, process, or performance, are called special ceramics. Special ceramics have great potential due to their many unique properties. Moreover, the main raw materials for making special ceramics are abundant on the earth, cheap and easily available. In the past 20 years, major industrial countries have attached great importance to the development and research of special ceramics, forming a worldwide "ceramic fever", and have made great progress. Therefore, special ceramics are known as "universal ceramics" and are one of the most promising new materials in the 21st century.
Boron carbide is an important special ceramic with many excellent properties. Boron carbide was first discovered in 1858, and then B3C and B6C were prepared and identified by Joly of England in 1883 and Moissan of France in 1894. Compounds with a stoichiometric molecular formula of B4C were not recognized until 1934. Subsequently, Russian scholars proposed many different molecular formulas for carbon boron compounds, but these molecular formulas were not confirmed. In fact, from the B-C phase diagram, it can be seen that carbon boron compounds have a very wide homogeneous region from B4.0C to B10.5C, and the substances in this homogeneous region are commonly known as boron carbide. Since the 1950s, a lot of research has been conducted on boron carbide, especially its structure and properties, and many research results have been achieved, promoting the rapid development of boron carbide preparation and application technology. Due to the excellent performance of boron carbide that is unmatched by other materials, people have continuously increased the depth and intensity of research on boron carbide ceramics. In addition to the continuous emergence of new methods for synthesizing high-purity and ultra-fine boron carbide powder, people are more committed to conducting advanced and practical molding and sintering process technology research, so that boron carbide products can be applied in certain high-tech fields and further industrialized production.
The hardness of boron carbide is second only to diamond and cubic boron nitride in nature, and its nearly constant high-temperature hardness (>30 GPa) is unparalleled in other materials, making it an important member of the superhard material family. In boron carbide, boron and carbon are mainly bonded by covalent bonds (>90%), characterized by high melting point (2450 ℃), high hardness, high modulus, low density (2.52 g/cm3), good wear resistance, strong acid and alkaline resistance, and good neutron and oxygen absorption capabilities, and low expansion coefficient (5.0 × 10-6 · K-1), thermoelectric performance (140s/m, room temperature), so it is widely used in refractory materials, engineering ceramics, nuclear industry, aerospace and other fields. However, due to its low fracture toughness, high sintering temperature, poor oxidation resistance, and poor metal stability, boron carbide has limited its further application in industry. Therefore, researchers at home and abroad have conducted a lot of research on improving the performance of boron carbide ceramics, and proposed the concept of boron carbide multiphase ceramics. For example, several important new material development plans (such as the HILTI plan and the COST plan) formulated by the European Commission for Science and Technology in the 1980s included the exploration and research of boron carbide (based) superhard material systems. Recent literature indicates that due to the limitations of boron carbide itself, it is difficult to significantly improve its mechanical properties through process optimization. However, with the development of ultrafine powder preparation technology and the development of effective sintering aids, conventional sintering of boron carbide has become possible, and boron carbide materials have been widely used in civil, aviation, and military fields.
Currently, structural ceramics used for bulletproof ceramics mainly include aluminum oxide, silicon carbide, and boron carbide. Among them, boron carbide is the armor material with the best bulletproof performance, and is currently used as aircraft armor material and special purpose protective structures. Although aluminum oxide has the lowest comprehensive protection coefficient, it has been widely used in armor and armored vehicles due to its lowest cost. Silicon carbide bulletproof ceramics are between the two in terms of protection coefficient and cost. Therefore, the research on reducing the cost of boron carbide bulletproof ceramic materials has a strong necessity and broad application prospects.