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A cermet is a composite material composed of ceramic and metal materials.
A cermet can combine attractive properties of both a ceramic, such as high temperature resistance and hardness, and those of a metal, such as the ability to undergo plastic deformation. The metal is used as a binder for an oxide, boride, or carbide. Generally, the metallic elements used are nickel, molybdenum, and cobalt. Depending on the physical structure of the material, cermets can also be metal matrix composites, but cermets are usually less than 20% metal by volume.
Cermets are used in the manufacture of (especially ), , and other electronics components which may experience high temperature.
Cermets are used instead of tungsten carbide in saws and other brazing tools due to their superior wear and corrosion properties. Titanium nitride (TiN), titanium carbonitride (TiCN), titanium carbide (TiC) and similar can be brazed like tungsten carbide if properly prepared, however they require special handling during grinding.
Composites of MAX phases, an emerging class of ternary carbides or nitrides with aluminium or titanium alloys 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 and orbital debris much more effectively than more traditional spacecraft materials, such as aluminum and other metals.
After World War II, 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 , as well as high temperature turbine blades. Today, ceramics are routinely implemented in the combustor 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 rotational acceleration (“spool-up time”) 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, University of Illinois, and Rutgers University.
The word cermet was actually coined by the United States Air Force, the idea being that they are a combination of two materials, a Ceramic and a Metal. Ceramics possess basic physical properties such as a high melting point, chemical stability, and especially redox. Basic physical properties of metals include ductility, high strength, and high thermal conductivity.
The first ceramic metal material developed used magnesium oxide (MgO), beryllium oxide (BeO), and Aluminium oxide (Al2O3) for the ceramic part. Emphasis on high stress rupture strengths was around 980 °C.Metallurgical Concepts, "Creep and Stress Rupture". 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, Pennsylvania, 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 nucleation 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 studied more closely. Both materials possessed better thermal shock resistance, high strength, and moderate thermal conductivity.
===Cermet production, Helipot Division of Beckman Instruments, 1966===
Ceramic-to-metal have also been used. Traditionally they have been used in fuel cells 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
One important use of bioceramics is in hip replacement surgery. The materials used for the replacement were usually metals such as titanium, 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.Design Fax Online, "Hybrid Hip Joint".
are also used in dentistry as a material for fillings and prostheses.
Cermets are also used in machining on cutting tools.
Cermets are also used as the ring material in high-quality line guides for fishing rods.
A cermet of depleted fissile material (e.g. uranium, plutonium) and sodalite has been researched for its benefits in the storage of nuclear waste.http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APCPCS000532000001000089000001&idtype=cvips&gifs=yes 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. Thanks to the size of the particles (~5 nm), surface plasmons on the metallic particles are generated and enable the heat transmission.
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