A cermet is a composite material composed of ceramic (cer) and metallic (met) materials. Composite materials (or composites for short are engineered Materials made from two or more constituent materials with significantly different physical or chemical The word ceramic is derived from the Greek word κεραμικός ( keramikos) The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across A cermet is ideally designed to have the optimal 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 word ceramic is derived from the Greek word κεραμικός ( keramikos) In Materials science, deformation is a change in the shape or size of an object due to an applied force. The metal is used as a binder for an oxide, boride, carbide, or alumina. An oxide is a Chemical compound containing at least one Oxygen atom as well as at least one other element In chemistry a boride is a chemical compound between boron and a less electronegative element For the Software development tool targeting the Symbian OS, see Carbide Generally, the metallic elements used are nickel, molybdenum, and cobalt. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. 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. A metal matrix composite (MMC is Composite material with at least two constituent parts one being a Metal.
Cermets are used in the manufacture of resistors (especially potentiometers), capacitors, and other electronic components which may experience high temperatures. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | A potentiometer is a three-terminal Resistor with a sliding contact that forms an adjustable Voltage divider. A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical
In the tool world, tungsten carbide is considered a cermet although tungsten carbide is so widely used that it is considered a class by itself. Tungsten carbide, WC, or tungsten semicarbide, W2C, is a chemical compound containing Tungsten and Carbon, similar
Cermets are being used instead of tungsten carbide in saws and other brazed tools due to their superior wear and corrosion properties. TiCN, TiC, TiN and similar can be brazed like tungsten carbide if properly prepared however they require special handling during grinding.
More complex materials, know as Cermet 2 or Cermet II, are being utilized since they give considerably longer life in cutting tools while both brazing and grinding like tungsten carbide.
Some types of cermets are also being considered for use as spacecraft shielding as they resist the high velocity impacts of micrometeoroids and orbital debris much more effectively than more traditional spacecraft materials such as aluminum and other metals. A Micrometeoroid (also micrometeorite, micrometeor) is a tiny Meteoroid; a small particle of rock in space usually weighing less than a Gram Space debris or orbital debris, also called space junk and space waste are the objects in Orbit around Earth created by humans that no
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History[1]
After World War II, the need to develop high temperature and high stress-resistant materials in the US became clear. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including 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. specific --->A jet engine is a Reaction engine that discharges a fast moving jet of Fluid to 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, University of Illinois, and Rutgers University. The Ohio State University ( OSU) is a Coeducational public Research university in the state of Ohio. This article is about the flagship campus For other uses and locations of University of Illinois, see University of Illinois (disambiguation The University of Rutgers The State University of New Jersey (also known as Rutgers University) is the largest institution for higher education in the state of New Jersey
The word cermet was actually coined by the United States Air Force, the idea being that they are a combination of two materials, a metal and a ceramic. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across The word ceramic is derived from the Greek word κεραμικός ( keramikos) Basic physical properties of metals include ductility, high strength, and high thermal conductivity. Ductility is a mechanical property used to describe the extent to which materials can be deformed plastically or "stretched" into "wires" without In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. Ceramics possess basic physical properties such as a high melting point, chemical stability, and especially oxidation resistance. The melting point of a solid is the temperature range at which it changes state from solid to Liquid. Redox (shorthand for reduction-oxidation reaction describes all Chemical reactions in which atoms have their Oxidation number ( Oxidation state
The first ceramic metal material developed used magnesium oxide (MgO), Beryllium oxide (BeO), and aluminum oxide (Al2O3) for the ceramic part. Magnesium oxide, or magnesia, is a white solid Mineral that occurs naturally as Periclase and is a source Beryllium oxide ( BeO) is a white crystalline oxide It is notable as it is an electrical insulator with a thermal conductivity higher than any other non-metal that actually Emphasis on high stress rupture strengths was around 980C. [2] Ohio State University was the first to develop Al2O3 based cermets with high stress rupture strengths around 1200C. Kennametal, a metal-working and tool company based in Latrobe, PA, developed the first titanium carbide cermet with a 2800 psi and 100 hour stress-to-rupture strength at 980C. Kennametal is a metalworking and tool production company headquartered in Latrobe Pennsylvania, a city some 50 miles from Pittsburgh. Latrobe (leɪˈtʃroʊb is a City in Westmoreland County, Pennsylvania, United States approximately 40 miles southeast of Pittsburgh 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 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.
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. [3] Today, cermet vacuum tube coatings have proved to be key to solar hot water systems.
Ceramic-to-metal mechanical seals have also been used. A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage (e Traditionally they have been used in fuel cells and other devices that convert chemical, nuclear, or thermionic energy to electricity. A fuel cell is an electrochemical conversion device It produces electricity from Fuel (on the Anode side and an oxidant (on the The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven generators designed to operate in corrosive liquid-metal vapors. [3]
Bioceramics
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, a material chemically similar to bone structure, can integrate and help bone grow into it. Hydroxylapatite, also called hydroxyapatite, is a Mineral. It is a naturally occurring form of calcium Apatite with the formula Ca5(PO43(OH 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, also hip Arthroplasty, is a surgical procedure in which the Hip joint is replaced by a prosthetic implant. A hip joint essentially is a multiaxial ball and socket. The materials used for the replacement hip joints were usually metals such as titanium with the hip socket usually lined with plastic. Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 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. [4]
Cermets are also used in dentistry as a material for fillings and prostheses. Dentistry' is the "evaluation diagnosis prevention and/or treatment (nonsurgical surgical or related procedures of diseases disorders and/or conditions of the oral cavity
Cermets in transportation
Ceramic parts have been used in conjunction with metal parts as friction materials for brakes and clutches. A brake is a device for slowing or stopping the motion of a Machine or Vehicle, or alternatively a device to restrain it from starting to move again A clutch is a mechanism for transmitting rotation which can be engaged and disengaged [3]
Other applications
The United States Army and British Army has had extensive research in the development of cermets. The United States Army is a military organization whose primary mission is to "provide necessary forces and capabilities. The British Army is the land armed forces branch of the British Armed Forces. These include the development of lightweight ceramic projectile proof armor for soldiers and also Chobham armor. Chobham armour is the name informally given to a Composite armour developed in the 1960s at the British Tank research centre on Chobham Common
Cermets are also used in machining on cutting tools.
A cermet of depleted fissiable material (e. g. uranium, plutonium) and sodalite has been researched for its benefits in the storage of nuclear waste. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Sodalite is a rich royal blue Mineral widely enjoyed as an Ornamental stone. [5] Similar composites have also been researched for use as a fuel source. [6]
See also
Notes
- ^ >Tinklepaugh, James R. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy The nuclear fuel cycle, also called nuclear fuel chain, is the progression of Nuclear fuel through a series of differing stages : "Cermets. ", Reinhold Publishing Corporation, 1960
- ^ Metallurgical Concepts, "Creep and Stress Rupture". http://www.materialsengineer.com/CA-Creep-Stress-Rupture.htm
- ^ a b c 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
- ^ Design Fax Online, "Hybrid Hip Joint". http://www.manufacturingcenter.com/dfx/archives/0503/0503app_ideas.asp
- ^ http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=APCPCS000532000001000089000001&idtype=cvips&gifs=yes
- ^ http://e-archive.library.okstate.edu/mech_researchweek/2/
Further reading
- Tinklepaugh, James R. (1960). Cermets. New York: Reinhold Publishing Corporation. ASIN B0007E6FO4.
External links
Dictionary
cermet
-noun
- A composite material composed of ceramic and metal materials, used in such applications as industrial saws and turbine blades.
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