Ceramic Metallics ,Cermet

Product Information

A cermet is a composite material composed of ceramic (cer) and metal (met) 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.

It's ideal for enduring harsh conditions, and some options are capable of conducting electricity, bending and flexing. A cermet surface is made up of two parts. The ceramic acts as a matrix or base held together with the metal components throughout the structure. Imagine cermet as a net where the net itself is made of metal, and the holes in between are filled with ceramic. However, cermet can also be configured in the opposite way, where the metal makes up the matrix that the ceramic holds together. Cermet not only maintains high strength, high hardness, wear resistance, high-temperature resistance, oxidation resistance and chemical stability of ceramics, but also has good mental toughness and plasticity. The characteristics of cermet mainly include the following aspects:

(1) The wettability of metal to ceramic phase is good. The wettability between metal and ceramic particles is one of the main conditions to evaluate the microstructure and properties of cermet. The stronger the wetting ability is, the more likely the metal forms a continuous phase, and the better the cermet is.

(2) There is no severe chemical reaction between the metal phase and the ceramics. If the interfacial reaction is intense and the compound is formed in the preparation of cermet, it is impossible to improve the resistance of ceramics to mechanical shock and thermal shock by using metal phase.

(3) The expansion coefficient between the metal phase and the ceramic phase will not be too large. When the expansion coefficients of the cermet and metal phases differ greatly, the internal stress will be increased and the thermal stability of cermet will be reduced.

Cermets are used instead of tungsten carbide in saws and other brazed 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,[1] 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 micrometeoroids and orbital debris much more effectively than more traditional spacecraft materials such as aluminum and other metals

Classification of cermets

Oxide based cermets

Oxide-based cermets are composed of alumina, zirconia, magnesium oxide, beryllium oxide and tungsten, chromium or cobalt. They are characterized by high-temperature resistance, chemical corrosion resistance, good thermal conductivity and high mechanical strength.

The wettability between Cr and Al2O3 is not good, but a dense layer of Cr2O3 is easily formed on the surface of metal chromium powder, so the interfacial energy between them can be reduced and the wettability can be improved by forming Al2O3-Cr2O3 solid solution. In order to make the metal chromium oxidized partially, some measures are often adopted, such as introducing trace water vapor or oxygen into the sintering atmosphere, replacing alumina with a part of Al (OH) 3 in the batching, and replacing metal chromium with a part of chromium oxide in the batching. Al2O3-Cr cermets are made from 99.5% purity of a-Al2O3 and 99% purity of electrolytic Cr powder. Al2O3 and Cr powder are dried or wet ground together to the necessary size composition, which can be formed by any molding method.

Carbide Based Cermets

Carbide based cermets. Titanium carbide, silicon carbide, tungsten carbide and other metals as the matrix, and metal cobalt, nickel, chromium, tungsten, molybdenum composite, with high hardness, high wear resistance, high temperature and other characteristics. Here is a brief introduction to titanium carbide (TiC) cermets.

TiC has the high melting point, high hardness, high elastic modulus, good thermal shock resistance and chemical stability, and its high-temperature oxidation resistance is only lower than that of SiC. Titanium carbide is an important raw material of cemented carbide, so it is widely used as a hard phase in structural materials to make titanium carbide-based cermets such as wear-resistant materials, cutting tool materials, mechanical parts, etc. It is a heterogeneous composite material composed of metal or alloy with titanium carbide ceramic phase, which keeps the ceramic high. The strength, hardness, wear resistance, high-temperature resistance, oxidation resistance and chemical stability are also good. Because of these excellent physical and chemical properties, titanium carbide based cermets have attracted much attention.

Boride Cermet

Boride ceramics are interstitial compounds. Many complex covalent bonds can be formed between boron and boron. At the same time, boron can form ion bonds with many metal atoms. This characteristic determines that boride has high melting point, high hardness, high wear resistance and high corrosion resistance, so it is widely used in cemented carbide materials and wear resistant materials. In boride ceramics, binary borides such as TiB2, ZrB2 and CrB2 are considered as the most promising boride ceramics because of their excellent properties. However, due to the strong chemical reaction between binary boride ceramics such as TiB2 and metal matrix, the sintering performance will deteriorate. The research on the practical application of three element boride cermet in the industrial field remains to be further studied. The existing problems include: (1) Because ternary boride cermet mainly uses molybdenum powder, ferroboron alloy powder, nickel powder and chromium powder as main raw materials, the production cost is high. (2) The reliability and reproducibility of the three element boride cermet are poor.

Titanium Nitride-Based Cermets

In 1956, Ford Motor Company discovered that adding molybdenum alloy to TiC-Ni based cermets could improve the wettability of Ni to TiC and greatly enhance the strength of the alloy. In 1971, Kieffer et al. found that the addition of TiN into TiC-Mo-Ni cermets could not only significantly refine the hard phase grains, improve the mechanical properties of Cermets at room and high temperature, but also greatly improve the high-temperature corrosion resistance and oxidation resistance of cermets. Therefore, TiC(N)) cermets based on titanium carbide nitride were very popular at home and abroad. Attention has been made and systematic studies have been carried out. Since the 1980s, Ti (C, N) based cermets have developed rapidly. Cemented carbide manufacturers all over the world have introduced a series of Ti (C, N) based cermets tools. Over the past 30 years, with the development of powder metallurgy technology, composition evolution tends to be stable, sintering technology is constantly updated, powder size is constantly refined, Ti (C, N) based cermet has developed to a relatively mature stage.

Application of Cermet

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

Bioceramics

One important use of bioceramics is in hip replacement surgery. The materials used for the replacement hip joints 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

Transportation

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

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

Cermets are also used in machining on cutting tools.

Cermet tools have high hardness, red hardness and wear resistance, and excellent cutting performance in high-speed cutting and dry cutting. Under the same cutting conditions, the wear resistance of cermet tools is much higher than that of ordinary cemented carbide.

Cermets are also used as the ring material in high-quality line guides for fishing rods.

Aerospace Industry

TiC-Ni cermets have been used as high-temperature materials for jet engine blades since the 1950s. However, TiC particles agglomerate and grow up during sintering because nickel can not completely wet TiC, which results in poor toughness of the materials and fails to be used as heat-resistant materials. TiC itself has high hardness, high melting point, low specific gravity and good thermal stability, while copper has excellent electrical conductivity, thermal conductivity and good plasticity. TiC/Cu composites composed of TiC and metallic copper synthesize the excellent properties of both and have the application as conductive, thermally conductive, wear-resistant materials and materials for rocket throat lining.

Cermet composite coating can change the appearance, structure and chemical composition of the outer surface of the metal matrix, and give the matrix new properties. Cermet composite coating is a kind of excellent composite material with the advantages of strength and toughness of metal and high-temperature resistance of ceramics. It has been successfully applied to aerospace, aviation, national defense, chemical industry, machinery, power, and electronics industries. The ceramic lined composite pipe has better performance than ceramic lined pipe. Self-propagating high-temperature synthesis centrifugal casting of liner ceramics can be used as corrosion-resistant pipelines for transportation of petroleum or chemical products and semi-products, as anti-wear pipelines for mines, as slurry transportation pipelines in ore dressing plants, and as water pipelines with muddy sand.