Titanium nitride and its Characteristics

Titanium nitride (TiN; sometimes called Tinite) is an extremely hard ceramic material commonly used as a physical vapor deposition (PVD) coating on titanium alloys, steel, carbide, and aluminum components to improve the surface of the substrate performance.

Applied as a thin coating, TiN is used to harden and protect cutting and sliding surfaces, for decorative purposes (due to its golden appearance), and as a non-toxic outer layer for medical implants. Coating thickness less than 5 microns (0.00020 inches) in most applications.

Characteristics 

TiN has a Vickers hardness of 1800–2100, an elastic modulus of 251 GPa, a thermal expansion coefficient of 9.35×10−6 K−1, and a superconducting transition temperature of 5.6 K.TiN oxidizes at 800 °C in normal atmosphere.TiN is brown in color and golden in color when used as a coating.According to laboratory tests, it is chemically stable at 20 °C, but it is slowly attacked by concentrated acid solutions as the temperature increases.Depending on the substrate material and surface finish, the coefficient of friction of TiN with another TiN surface (unlubricated) ranges from 0.4 to 0.9. A typical TiN structure has a NaCl-type crystal structure with a stoichiometric ratio of about 1:1; however, TiNx compounds with x ranging from 0.6 to 1.2 are thermodynamically stable.TiN becomes superconducting at low temperatures, with a critical temperature as high as 6.0 K for single crystals.Superconductivity in thin-film TiN has been extensively studied, and its superconducting properties vary widely depending on sample preparation, up to complete suppression of superconductivity at the superconductor-insulator transition.The TiN film was cooled to near absolute zero, transforming it into the first known superinsulator, with a sudden 100,000-fold increase in resistance.

Uses

A well-known use of TiN coatings is for edge retention and corrosion resistance of machine tool tools such as drills and milling cutters, often increasing their service life by a factor of three or more.Because of its metallic gold color, TiN is used to adorn costume jewelry and automotive trim.TiN is also widely used as a top coat, often with nickel (Ni) or chromium (Cr) plated substrates on consumer plumbing and door hardware.As a coating, it is used in aerospace and military applications to protect the sliding surfaces of bicycle and motorcycle suspension forks and the shock shafts of radio-controlled automobiles.TiN is also used as a protective coating on the moving parts of many rifles and semi-automatic firearms because it is very durable.In addition to being durable, it's super smooth and removes carbon buildup very easily.TiN is non-toxic, meets FDA guidelines, and has been used in medical devices such as scalpel blades and orthopedic bone saw blades, where sharpness and edge retention are important.TiN coatings are also used in implant prostheses (especially hip replacement implants) and other medical implants.

Although less obvious, TiN films are also used in microelectronics, where they serve as conductive connections between active devices and metal contacts used to operate circuits, while also acting as a diffusion barrier to stop the metal from diffusing into the silicon.In this case, TiN is classified as a "barrier metal" (resistivity ~25 µΩ cm[2]), although it is clearly a ceramic from the standpoint of chemical or mechanical behavior.Recent chip designs using 45nm technology and beyond also use TiN as the "metal" to improve transistor performance.Combined with a gate dielectric with a higher dielectric constant than standard SiO2 (such as HfSiO), the gate length can be scaled down with low leakage, higher drive current and equal or better threshold voltage.Furthermore, TiN thin films are currently being considered for coating zirconium alloys for accident-tolerant nuclear fuels.It is also used as a coating on some compression driver diaphragms to improve performance.

Due to its high biostability, TiN layers can also be used as electrodes in bioelectronic applications such as smart implants or in vivo biosensors that must withstand severe corrosion caused by body fluids.TiN electrodes have been used in subretinal prosthetic projects and in biomedical microelectromechanical systems (BioMEMS).