Titanium nitride
1835568
220817086
2008-06-21T18:58:01Z
78.14.42.21
Nanoindentation tests are required, not microhardness (the reference is not correct)
[[image:Titanium nitride coating.jpg|thumb|150px|TiN coated drill|right]]
[[image:Paraframe.jpg|thumb|75px|Dark gray TiCN coating on a [[Gerber_Legendary_Blades|Gerber]] pocketknife|right]]
'''Titanium nitride''' ({{titanium}}{{nitrogen}}) (sometimes known as Tinite or TiNite) is an extremely hard [[ceramic]] material, often used as a coating on [[titanium alloy]], [[steel]], [[carbide]], and [[aluminium]] components to improve the substrate's surface properties.
Applied as a thin coating, TiN is used to harden and protect cutting and sliding surfaces, for decorative purposes, and as a non-toxic exterior for medical implants.
==Characteristics==
The hardness of TiN coatings is difficult to measure as the coatings are exceptionally hard and the thinness of the coating causes conventional hardness tests to penetrate into the substrate. [[Nanoindentation]] hardness tests are required for accurate readings. The hardness of TiN is estimated as ~85 on the [[rockwell scale|Rockwell C Hardness]] (~2500 [[Vickers Hardness]] or 24.5 [[gigapascal]]s). The Rockwell C scale is regarded as crude for readings this high.<ref>[http://www.brycoat.com BryCoat Titanium Nitride].</ref> Special techniques have been developed to measure TiN hardness.<ref>[http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JVTAD6000009000004002543000001&idtype=cvips&gifs=yes Hardness and elastic modulus of TiN based on continuous indentation technique and new correlation]</ref>
TiN has excellent [[infrared]] (IR) reflectivity properties, reflecting in a spectrum similar to elemental [[gold]] (Au). Depending on the substrate material and surface finish, TiN will have a [[coefficient of friction]] ranging from 0.4 to 0.9 versus itself (non-lubricated). Typical formation has a [[crystal structure]] of [[Sodium chloride|NaCl]]-type with a roughly 1:1 [[stoichiometry]]; however TiN<sub><i>x</i></sub> compounds with <i>x</i> ranging from 0.6 to 1.2 are thermodynamically stable<ref>L.E. Toth, Transition Metal Carbides and Nitrides (Academic, New York, 1971)</ref>. TiN will oxidize at 600 °C (~1100 °F) at normal atmosphere, and has a melting point of 2930 °C.
== Uses ==
The most common use for TiN coating is for edge retention and corrosion resistance on machine tooling, such as [[drill bit]]s and [[milling cutter]]s, often improving their lifetime by a factor of three or more.<!-- It would be helpful to have a reference here to back up this claim. -->
Because of TiN's metallic gold color, it is used to coat [[costume jewelry]] and automotive trim for decorative purposes. TiN is also widely used as a top-layer coating, usually with [[nickel]] (Ni) or [[chromium]] (Cr) plated substrates, on consumer plumbing fixtures and door hardware. TiN is non-toxic, meets [[Food and Drug Administration|FDA]] guidelines and has seen use in [[medical devices]] such as scalpel blades and orthopedic bone saw blades where sharpness and edge retention are important <ref>[http://www.ionfusion.com IonFusion Surgical].</ref> and [[bio-implants]], as well as [[aerospace]] and military applications.
Such coatings have also been used in implanted [[prosthesis|prostheses]] (especially [[hip replacement]] implants). Such films are usually applied by either reactive growth (for example, [[Annealing (metallurgy)|annealing]] a piece of titanium in [[nitrogen]]) or [[physical vapor deposition]] (PVD), with a depth of about 3 [[micrometre|micrometers]]. Its high [[Young's modulus]] (600 [[gigapascal]]s)<ref>[http://www.matweb.com MatWeb].</ref> relative to titanium alloys (100 GPa) means that thick coatings tend to flake away, making them much less durable than thin ones.
As a coating it is also used to protect the sliding surfaces of [[suspension (vehicle)|suspension]] forks of [[bicycle]]s and [[motorcycle]]s as well as the shock shafts of [[radio controlled car]]s.
Though less visible, [[thin film]]s of TiN are also used in the [[Fabrication (semiconductor)|semiconductor]] industry. In [[copper-based chips]], such films find use as a [[electrical conductivity|conductive]] barrier between a [[silicon]] device and the metal contacts used to operate it. While the film blocks [[diffusion]] of metal into the silicon, it is conductive enough (30–70 μ[[Ohm|Ω]]·[[Centimeter|cm]]) to allow a good electrical connection. In this context, TiN is classified as a "[[barrier metal]]", even though it is clearly a ceramic from the perspective of [[chemistry]] or mechanical behavior.
Led by Argonne senior scientist Valerii Vinokur and Russian scientist Tatyana Baturina, an international team of scientists from Argonne, Germany, Russia and Belgium fashioned a thin film of titanium nitride which they then chilled to near absolute zero. This converts the material to a superinsulator, with resistance suddenly increased by a factor of 100,000. Newly discovered '[[Superinsulator]]s' promise to transform materials research.<ref>[http://www.physorg.com/news126797387.html Newly discovered 'superinsulators' promise to transform materials research, electronics design<!-- Bot generated title -->]</ref>
==Fabrication==
The most common methods of TiN thin film creation are [[physical vapor deposition]] (PVD, usually [[sputter deposition]], [[Cathodic Arc Deposition]] or [[electron beam]] heating) and [[chemical vapor deposition]] (CVD). In both methods, pure titanium is [[Sublimation (physics)|sublimated]] and reacted with nitrogen in a high-energy, [[vacuum]] environment. PVD is preferred for steel parts because the deposition temperatures lie beyond the austenitizing temperature of steel. PVD applied TiN is also for a variety of relatively higher melting point materials such as stainless steels, Titanium and Titanium alloys. <ref>[http://www.servicecoating.com Home Page<!-- Bot generated title -->]</ref>
Bulk [[ceramic]] objects can be fabricated by packing powdered metallic titanium into the desired shape, compressing it to the proper density, then igniting it in an atmosphere of pure nitrogen. The heat released by the chemical reaction between the metal and gas is sufficient to [[sintering|sinter]] the nitride reaction product into a hard, finished item. See [[powder metallurgy]].
==Other commercial variants==
There are several commercially-used variants of TiN that have been developed in the past decade, such titanium carbon nitride (TiCN) and [[titanium aluminium nitride]] (TiAlN), which may be used individually or in alternating layers with TiN. These coatings offer similar or superior enhancements in corrosion resistance and hardness, and additional colors ranging from light gray to nearly black, to a dark iridescent bluish-purple depending on the exact process of application. These coatings are becoming common on sporting goods, particularly [[knife|knives]] and [[handgun]]s, where they are used for both cosmetic and functional reasons.<ref>[http://www.mmicoating.com Molecular Metallurgy, Inc.]</ref>
==As a constituent in steel making==
Titanium nitride is also an intentional product in many steels, not on their surface. TiN forms at very high temperatures because of its very low [[enthalpy]] of formation, and even nucleates directly from the melt in secondary steelmaking. It forms discrete, micrometre-sized [[cubic]] particles at [[grain boundaries]] and triple points, and because of its low solubility in [[austenite]], the [[face centred cubic]] phase of steel that most exist in at the high temperatures forming operations usually take place at, prevents grain growth by [[Ostwald ripening|Ostwald Ripening]] up to very high [[homologous temperature|homologous temperatures]]. Titanium nitride has the lowest solubility product of any metal nitride or carbide in austenite, and as a result is often intentionally produced by judicious additions of titanium to the alloy.
==References==
<references/>
==External links==
[[Category:Nitrides]]
[[Category:Titanium compounds]]
[[Category:Semiconductor device fabrication]]
[[Category:Metals processes]]
[[Category:Superhard materials]]
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