In order to make ceramics resistant to high temperatures and not easy to break, people add some metal powder to the clay used to make ceramics, thus making cermets.
A composite material composed of one or several ceramic phases and metal phases or alloys. In a broad sense, cermets also include refractory compound alloys, hard alloys, and metal-bonded diamond tool materials. The ceramic phase in cermet is an oxide or refractory compound with high melting point and high hardness, and the metal phase is mainly transition elements (iron, cobalt, nickel, chromium, tungsten, molybdenum, etc.) and their alloys. Cermet not only has the toughness, high thermal conductivity and good thermal stability of metal, but also has the characteristics of high temperature resistance, corrosion resistance and wear resistance of ceramics. According to the different percentages of the constituent phases, cermets are divided into two types: ceramic-based and metal-based.
Ceramic-based cermets mainly include: ①Oxide-based cermets. It is made of aluminum oxide, zirconium oxide, magnesium oxide, beryllium oxide, etc. as the matrix, compounded with metal tungsten, chromium or cobalt. It has the characteristics of high temperature resistance, chemical corrosion resistance, good thermal conductivity, and high mechanical strength. It can be used as a missile nozzle Bushes, crucibles for melting metals and metal cutting tools. ②Carbide-based cermet. It is made of titanium carbide, silicon carbide, tungsten carbide, etc. as the matrix, compounded with metal cobalt, nickel, chromium, tungsten, molybdenum and other metals. It has the characteristics of high hardness, high wear resistance, high temperature resistance, etc., used to make cutting tools, High temperature bearings, sealing rings, wire picking die sets and turbine blades. ③Nitride-based cermet. With titanium nitride, boron nitride, silicon nitride and tantalum nitride as the matrix, it has super-hardness, thermal vibration resistance and good high-temperature creep properties, and is less used.
Metal-based cermets are made by adding fine oxide powder to the metal matrix, also known as dispersion-reinforced materials. There are mainly sintered aluminum (aluminum-alumina), sintered beryllium (beryllium-beryllium oxide), TD nickel (nickel-thorium oxide) and so on. The alumina content in sintered aluminum is about 5% to 15%. Compared with alloy aluminum, it has high high-temperature strength, low density, easy processing, corrosion resistance and good thermal conductivity. Commonly used in the manufacture of aircraft and missile structural parts, engine pistons, chemical machinery parts, etc.
Cermet has the advantages of metal and ceramics. It has low density, high hardness, wear resistance, good thermal conductivity, and will not be brittle due to sudden cold or sudden heat. In addition, coating a ceramic coating with good air tightness, high melting point and poor heat transfer performance on the metal surface can also prevent the metal or alloy from oxidizing or corroding at high temperatures.
Cermets are widely used in rockets, missiles, supersonic aircraft shells, and flame nozzles in combustion chambers.
What are the advantages and uses of cermets?
2020 07/27