Advanced ceramics can be divided into structural ceramics, tool ceramics, and functional ceramics according to their different uses.
Structural Ceramics
The main materials of structural ceramics are alumina (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), and hexagon boron nitride ceramics (BN).
The main composition is Al2O3, and the general content is more than 45%. Alumina ceramics have various excellent properties such as high-temperature resistance, corrosion resistance and high strength, which is 2~3 ordinary ceramics. However, alumina ceramics have the disadvantage of being brittle and unable to accept sudden changes in ambient temperature. Alumina ceramics are widely used as the crucible, engine spark plug, high-temperature refractory, thermocouple sleeve, sealing ring and so on.
Silicon nitride (Si3N4) ceramics
Si3N4 is the main component of silicon nitride ceramics, which is a kind of high-temperature ceramics with high strength, high hardness, abrasion resistance, corrosion resistance, and self-lubrication. The linear expansion coefficient of silicon nitride is the smallest among all kinds of ceramics, and it has excellent electrical insulation and radiation resistance. It has excellent corrosion resistance, and it can withstand the corrosion of various acids except the hydrofluoric acid, as well as alkali, corrosion of various metals. Silicon nitride ceramics can be used as high-temperature bearings, sealing rings used in corrosive media, thermocouple sleeves, and metal cutting tools.
Silicon carbide ceramics (SiC)
Silicon carbide ceramics are mainly composed of SiC, which is a kind of high-temperature ceramic with high strength and high hardness. When used in the high temperature of 1200 ℃ ~ 1400 ℃, silicon carbide ceramics can still maintain a high bending strength. In addition, silicon carbide ceramics also have good thermal conductivity, oxidation resistance, electrical conductivity, and high impact toughness. It is a good high-temperature structural material and can be used for rocket tail nozzle, thermocouple sleeve, furnace tube, and other high-temperature components.
Hexagonal boron nitride (h-BN)
The main composition of hexagonal boron nitride ceramics is BN, and the crystal structure is hexagonal crystal system. The structure and performance of hexagonal boron nitride ceramics are similar to graphite, so it is known as “White Graphite “. Hexagonal boron nitride ceramics are of low hardness and can be machined with self-lubricating properties, and they can also be made into self-lubricating high-temperature bearings and glass-forming molds.
Tool Ceramics
The main materials of tool ceramics are cemented carbide, natural diamond (diamond), cubic boron nitride (CBN), etc.
Cemented carbide
Carbides are mainly composed of carbides and binders. Carbides mainly include WC, TiC, TaC, NBC, VC, etc., and binders are mainly cobalt (Co). Compared with the tool steel, cemented carbide has a high hardness (87 ~ 91 HRA), good red hardness (1000 ℃) and excellent wear resistance. When used as a cutter, its cutting speed is 4~7 times higher than that of HSS, and its service life is 5~8 times higher. However, its disadvantages are high hardness, brittle, and difficult to be machined, so it is often made into a blade and welded on the tool rod for use. Carbide is mainly used for machining tools; Various dies, including drawing die, drawing die, cold heading die; Mining tools, geology, and petroleum use a variety of drill bits, etc.
Natural diamond (diamond)
Natural diamond (diamond) is a precious ornament, while synthetic diamond is widely used in the industry. Diamond is the hardest material in nature and has a very high elastic modulus, and the thermal conductivity of diamond is the highest among known materials. Besides, diamond has good insulation, which can be used as the drill bit, cutter, grinding tool, drawing die, dressing tool. However, the thermal stability of the diamond tool is poor, and the affinity with iron group elements is large, so it cannot be used for processing iron, nickel-based alloy, but mainly for processing non-iron metal and non-metal, widely used in ceramics, glass, stone, concrete, gem, agate and other processing.
Tool Ceramics