A cermet is a

composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...

composed of

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...

(cer) and metal (met) materials. A cermet can combine attractive properties of both a

, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo

plastic deformation In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point on the object. Deflection is the relative change in external displacements on an object. Strain ...

. The metal is used as a binder for an

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some bo ...

, or

carbide In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of t ...

. Generally, the metallic elements used are

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow t ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lead ...

, and

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

. Depending on the physical structure of the material, cermets can also be

metal matrix composite In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carb ...

s, but cermets are usually less than 20% metal by volume. Cermets are used in the manufacture of

resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

s (especially

potentiometer A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrum ...

s),

capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

s, and other

electronic Electronic may refer to: *Electronics, the science of how to control electric energy in semiconductor * ''Electronics'' (magazine), a defunct American trade journal *Electronic storage, the storage of data using an electronic device *Electronic co ...

components which may experience high temperature. Cermets are used instead of tungsten carbide in saws and other

brazed Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal. Brazing differs from we ...

tools due to their superior wear and corrosion properties.

Titanium nitride Titanium nitride (TiN; sometimes known as Tinite) is an extremely hard ceramic material, often used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface prop ...

(TiN), titanium carbonitride (TiCN),

titanium carbide Titanium carbide, Ti C, is an extremely hard ( Mohs 9–9.5) refractory ceramic material, similar to tungsten carbide. It has the appearance of black powder with the sodium chloride ( face-centered cubic) crystal structure. It occurs in natur ...

(TiC) and similar can be brazed like

tungsten carbide Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...

if properly prepared, however they require special handling during grinding. Composites of

MAX phases The MAX phases are layered, hexagonal carbides and nitrides which have the general formula: Mn+1AXn, (MAX) where n = 1 to 4, and M is an early transition metal, A is an A-group (mostly IIIA and IVA, or groups 13 and 14) element and X is either carb ...

, an emerging class of ternary

carbides In chemistry, a carbide usually describes a compound composed of carbon and a metal. In metallurgy, carbiding or carburizing is the process for producing carbide coatings on a metal piece. Interstitial / Metallic carbides The carbides of the ...

nitrides In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...

with

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion i ...

alloys An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

have been studied since 2006 as high-value materials exhibiting favourable properties of ceramics in terms of hardness and compressive strength alongside ductility and fracture toughness typically associated with metals. Such cermet materials, including aluminium-MAX phase composites, have potential applications in automotive and aerospace applications. Some types of cermets are also being considered for use as spacecraft shielding as they resist the high velocity impacts of

micrometeoroid A micrometeoroid is a tiny meteoroid: a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through Earth's atmosphere and reaches Earth's surface. The term "micrometeor ...

s and

orbital debris Space debris (also known as space junk, space pollution, space waste, space trash, or space garbage) are defunct human-made objects in space—principally in Earth orbit—which no longer serve a useful function. These include derelict space ...

much more effectively than more traditional spacecraft materials such as aluminum and other metals.

HistoryTinklepaugh, James R.: "Cermets.", Reinhold Publishing Corporation, 1960

After

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

, the need to develop high temperature and high stress-resistant materials became clear. During the war, German scientists developed oxide base cermets as substitutes for alloys. They saw a use for this for the high-temperature sections of new jet engines as well as high temperature turbine blades. Today ceramics are routinely implemented in the combuster part of jet engines because it provides a heat-resistant chamber. Ceramic turbine blades have also been developed. These blades are lighter than steel and allow for greater acceleration of the blade assemblies. The United States Air Force saw potential in the material technology and became one of the principal sponsors for various research programs in the US. Some of the first universities to research were

Ohio State University The Ohio State University, commonly called Ohio State or OSU, is a public land-grant research university in Columbus, Ohio. A member of the University System of Ohio, it has been ranked by major institutional rankings among the best pub ...

University of Illinois The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Uni ...

, and

Rutgers University Rutgers University (; RU), officially Rutgers, The State University of New Jersey, is a public land-grant research university consisting of four campuses in New Jersey. Chartered in 1766, Rutgers was originally called Queen's College, and was ...

. The word cermet was actually coined by the

United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Si ...

, the idea being that they are a combination of two materials, a

metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...

and a

. Basic physical properties of metals include

ductility Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile str ...

, high strength, and high

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

. Ceramics possess basic physical properties such as a high

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

, chemical stability, and especially oxidation resistance. The first ceramic metal material developed used

magnesium oxide Magnesium oxide ( Mg O), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2� ...

(MgO),

beryllium oxide Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of ...

(BeO), and aluminum oxide (Al₂O₃) for the ceramic part. Emphasis on high stress rupture strengths was around 980 °C. Ohio State University was the first to develop Al₂O₃ based cermets with high stress rupture strengths around 1200 °C. Kennametal, a metal-working and tool company based in Latrobe, PA, USA, developed the first titanium carbide cermet with a and 100-hour stress-to-rupture strength at 980 °C. Jet engines operate at this temperature and further research was invested on using these materials for components. Quality control in manufacturing these ceramic metal composites was hard to standardize. Production had to be kept to small batches and within these batches, the properties varied greatly. Failure of the material was usually a result of undetected flaws usually

nucleated The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, ...

during processing. The existing technology in the 1950s reached a limit for jet engines where little more could be improved. Subsequently, engine manufactures were reluctant to develop ceramic metal engines. Interest was renewed in the 1960s when silicon nitride and silicon carbide were looked at more closely. Both materials possessed better thermal shock resistance, high strength, and moderate thermal conductivity.

Cermet production, Helipot Division of Beckman Instruments, 1966

File:Cermets 1 Steatite Ingredients Being Weighed 2012 002 5979.tiff , 1. Steatite Ingredients Being Weighed File:Cermets 2 Steatite Granulation Process Vibrating screen to separate steatite granules by size 2012 002 5979.tiff , 2. Steatite Granulation Process File:Cermets 3 Steatite Chip Pressing 2012 002 5979.tiff , 3. Steatite Chip Pressing File:Cermets 4 High Temperature Firing of Steatite Chip placing substrate in firing kilns 2012 002 5979.tiff , 4. High Temperature Firing of Steatite Chip File:Cermets 5 Cermet Substrate Screening 2012 002 5979.tiff , 5. Beckman Model 61 Potentiometer (Cermet Screening) File:Cermets 6 Final Firing of Cermet 2012 002 5979.tiff , 6. Final Firing of Cermet File:Cermets 7 Checking electrical resistance 2012 002 5979.tiff, 7. Checking electrical resistance File:Cermets 8 Final Assembly testing cermet elements for potentiometers 2012 002 5979.tiff , 8. Final Assembly

Applications

Ceramic-to-metal joints and seals

Cermets were first used extensively in ceramic-to-metal joint applications. Construction of vacuum tubes was one of the first critical systems, with the electronics industry employing and developing such seals. German scientists recognized that vacuum tubes with improved performance and reliability could be produced by substituting ceramics for glass. Ceramic tubes can be outgassed at higher temperatures. Because of the high-temperature seal, ceramic tubes withstand higher temperatures than glass tubes. Ceramic tubes are also mechanically stronger and less sensitive to thermal shock than glass tubes. Today, cermet vacuum tube coatings have proved to be key to solar hot water systems. Ceramic-to-metal

mechanical seal A mechanical seal is a device that helps join systems and mechanisms together by preventing leakage (e.g. in a pumping system), containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of ...

s have also been used. Traditionally they have been used in

fuel cells A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requ ...

and other devices that convert chemical, nuclear, or thermionic energy to electricity. The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven generators designed to operate in corrosive liquid-metal vapors.Pattee, H.E. "Joining Ceramics and Graphite to Other Materials, A Report." Office of Technology Utilization National Aeronautics and Space Administration, Washington D.C., 1968

Bioceramics

Bioceramics Bioceramics and bioglasses are ceramic materials that are biocompatible. Bioceramics are an important subset of biomaterials.J. F. Shackelford (editor)(1999) ''MSF bioceramics applications of ceramic and glass materials in medicine'' Bioceramics ...

play an extensive role in biomedical materials. The development of these materials and diversity of manufacturing techniques has broadened the applications that can be used in the human body. They can be in the form of thin layers on metallic implants, composites with a polymer component, or even just porous networks. These materials work well within the human body for several reasons. They are inert, and because they are resorbable and active, the materials can remain in the body unchanged. They can also dissolve and actively take part in physiological processes, for example, when

hydroxylapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...

, a material chemically similar to bone structure, can integrate and help bone grow into it. Common materials used for bioceramics include alumina, zirconia, calcium phosphate, glass ceramics, and pyrolytic carbons. One important use of bioceramics is in

hip replacement surgery Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant, that is, a hip prosthesis. Hip replacement surgery can be performed as a total replacement or a hemi (half) replacement. Such joint replacement o ...

. The materials used for the replacement

hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

s were usually metals such as

, with the hip socket usually lined with plastic. The multiaxial ball was tough metal ball but was eventually replaced with a longer-lasting ceramic ball. This reduced the roughening associated with the metal wall against the plastic lining of the artificial hip socket. The use of ceramic implants extended the life of the hip replacement parts. Dental cermets are also used in

dentistry Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the teeth, gums, and mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, disorders, and conditions of ...

as a material for fillings and prostheses.

Transportation

Ceramic parts have been used in conjunction with metal parts as friction materials for

brakes A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Backgroun ...

and

clutch A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...

es.

Electrical heaters

Cermets are used as heating elements in electric resistance heaters. One construction technique starts with the cermet material formulated as an ink, then prints it on a substrate and cures it with heat. This technique allows manufacture of complex shapes of heating elements. Examples of applications for cermet heating elements include thermostat heaters, heat sources for bottle sterilization, coffee carafe warmers, heaters for oven control, and laser printer fuser heaters.

Other applications

The

United States Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, ...

and

British Army The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. , the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkha ...

have had extensive research in the development of cermets. These include the development of lightweight ceramic projectile-proof armor for soldiers and also

Chobham armor Chobham armour is the informal name of a composite armour developed in the 1960s at the British tank research centre on Chobham Common, Surrey. The name has since become the common generic term for composite ceramic vehicle armour. Other n ...

. Cermets are also used in

machining Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...

cutting tools In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The majori ...

. Cermets are also used as the ring material in high-quality line guides for fishing rods. A cermet of depleted fissiable material (e.g.

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exh ...

) and sodalite has been researched for its benefits in the storage of nuclear waste. Similar composites have also been researched for use as a fuel form for nuclear reactors and nuclear thermal rockets. As nanostructured cermet, this material is used in the optical field, such as solar absorbers/

selective surface In solar thermal collectors, a selective surface or selective absorber is a means of increasing its operation temperature and/or efficiency. The selectivity is defined as the ratio of solar radiation absorption (αsol) to thermal infrared radi ...

. Thanks to the size of the particles (~5 nm), surface plasmons on the metallic particles are generated and enable the heat transmission. For reasons regarding luxury, cermet is sometimes found to be case materials for some watches, including

Jaeger-LeCoultre Manufacture Jaeger-LeCoultre SA, or simply Jaeger-LeCoultre (), is a Swiss luxury watch and clock manufacturer founded by Antoine LeCoultre in 1833 and is based in Le Sentier, Switzerland. Since 2000, the company has been a fully owned subsidiary ...

's Deep Sea Chronograph Vintage Cermet watch. It was also used (November 2019) on the bezel of the flagship diver Seiko Prospex LX Line Limited Edition watch.

Notes

External links

A Review of Fifty Years of Space Nuclear Fuel Development Programs
(broken) {{Authority control Composite materials