The Advantages and Applications of Cermets
In order to get the ceramic available to bear high-temperature and uneasy to be broken ,people added metal powders into the clay soil for ceramic ,so produced the cermets ,which is a composite material integrated one or several ceramic phases and metal or alloy phases. Generalized ceramic include refractory compound alloy ,tungsten carbide, diamond material with metal binder etc .In the cermets ,the ceramic phase is a oxidize with high melting temperature and hardness or refractory compound ;the metallic phase is the transition elements such as Iron,Cobalt,Nickel,Chrome,Tungsten,Molybodenu and their alloys. The cermets not only have the metallic performance such as toughness, high heat-conductivity and good thermal stability ,also have the ceramic’s characters like high temperature resistance,anti-corrusion and wear-resistance. Meanwhile, according to the occupation percentage of the ceramic or metallic phase in the material ,it divides into to two categories that ceramic-base and metallic-base .
The cermets with ceramic-base is sorted into 3 categories:
① Oxidize-base cermets, taking aluminum oxide, zirconium oxide, magnesium oxide, and beryllium oxide as substrate, and compounded with tungsten, chrome or cobalt respectively ,which has the performances such as high-temperature resistance,anti chemical corrosion, good thermal conductivity and high mechanical toughness etc .They are available to used as the missile nozzle insert, crucible of melting metals and metallic cutting tools.
② Carbide-base cermets, taking TiC,WC and SiC as the substrate ,compounded with cobalt,nickel,chrome,tungsten and molybdenum ,with high hardness ,wear-resistance and high-temperature resistance performances .They are available to be used as cutting tools, high-temperature bearing, sealing ring ,drawing die sleeve and turbine blade etc
③ Nitride-base cermets ,taking TiN,BN,SIN and TaN as substrates with high hardness, thermal vibration resistance and good high-temperature creep etc performances .They are rarely used .
The cermets with metallic-base is produced with adding of the oxidize fine powder ,also called diffusion-strengthen material which mainly includes sintered-aluminum,sintered-berylium,TD nickel etc .In the sintered-aluminum, oxidized-aluminum takes 5%~15%,comparing with aluminum alloy, its high temperature toughness, low density, easy to machine, good anti-corrosion ,good heat-conductivity etc performances are very apparent .They are commonly used as the structure components in producing air-plane and missile, engine piston and chemical machinery parts
Advantages of metal and ceramic, the cermets are low density, high hardness, excellent wear-resistance, good heat-conductivity and would not break or crack due to instant freezing or heating. In addition,coating a layer of cermets with performance as good air-sealing,high melting temperature ,bad heat-conductivity performances on the surface of the metals will prevent oxidization or corrosion in high temperature of the metals or alloys.
The cermets are widely used in these fields like rocket,missle,skell of supersonic plane and combustor of flame vents etc
