Titanium nitride belongs to a group of refractory metals in which a nonmetallic element (Nitrogen) forms a compound with a transition metal element (Titanium). This metallic compound has a brown color and appears gold when applied as a coating.
It possesses unique physical and chemical properties. For example, it exhibits superior characteristics to noble metals, such as high chemical stability, corrosion resistance, high mechanical hardness, and high-temperature durability.
Due to these superior properties, titanium nitride is used in a broad range of industrial applications. Its exceptional wear resistance quality makes it a perfect, high-performance coating material.
Titanium Nitride Profile
Chemical formula: TiN
Molecular weight: 61.87 g/mol
Melting point: 2947 °C
Max operating temp: 500 °C
Coating thickness: 1-5 microns
Corrosion resistance: Oxidation resistance up to 400 °C
Titanium nitride is mostly used as a coating material. A thin coating (usually less than 5 microns) is applied on steel, carbide, aluminum parts, and titanium alloys to enhance the surface properties of the substrate. It also utilized as a harmless exterior for medical implants.
How Titanium Nitride is Produced
A very small quantity of titanium nitride occurs in the natural form, which has been found in meteorites called Osbornite. Natural titanium nitride crystals are golden-yellow octahedrons. They are friable and do not dissolve in acids.
There are dozens of techniques used to synthesize titanium nitride. The most popular of them are:
1. Physical vapor deposition
The chemical reaction between titanium metal powder and nitrogen gas at high temperatures yields pure titanium nitride powder. There are several variations of this reaction, which include physical vapor deposition.
In one variation, for example, titanium compound is vaporized in a nitrogen plasma. In other variations, titanium metal is vaporized either by electron beam evaporation or low-pressure sputtering under nitrogen. In all cases, a thin film of TiN is deposited on a hot substrate heated up to 500°C.
2. A Non-Thermal Plasma Route
The reaction of ammonia (NH3) and titanium tetrachloride (TiCl4) is used to deposit a thin coating of TiN via chemical vapor deposition on a substrate heated to 1000 °C. This technique is based on a continuous-flow nonthermal plasma process, which leads to the formation of free-standing titanium nitride nanoparticles.
3. Using magnesium powder and ammonium chloride
Nanocrystalline TiN can also be prepared via a convenient route by the reaction of metallic magnesium power with ammonium chloride and titanium dioxide in an autoclave at 650 °C. This reaction yields cubic titanium nitride with an average size of 30 nanometers in diameter. It has impressive thermal stability and oxidation resistance below 350 °C in air.
Physical and Chemical Properties
Titanium nitride looks like dark gold when applied as a coating. At room temperature, it has a density of 5.2 g/cm3, which is almost twice the density of glass but lower than many metals.
TiN is extremely hard, compared to Corundum (crystallized alumina) used in abrasives. Its Vickers hardness range between 1800 and 2400. It has an electrical conductivity comparable to that of steel, and a superconducting transition temperature of -267.55 °C.
Titanium nitride is insoluble in water. At temperatures above 500 °C, it starts forming titanium oxides in a normal atmosphere.
While TiN remains chemically stable at 20 °C, lab experiments show that it can gradually dissolve in concentrated acid solution as the temperature increases. It can also be attacked by hot bases.
TiN becomes superconducting at temperatures below 150 °C. Thin-film titanium nitride has fascinating superconducting properties. For example, when it is cooled to near absolute zero, its resistance drastically increases by a factor of 100,000 once the temperature is dropped below a certain threshold.
Elastic modulus: 600 GPa
Shear modulus: 240 GPa
TiN is mostly applied as a coating with a thickness of 2 to 5 microns on the working surfaces. Various parameters affect the coating thickness, including the type of material, tool geometry, and external environment.
TiN shows excellent adhesiveness as long as the substrate is properly cleaned and the coating process is properly executed. The Coefficient Of Friction depends on the material the coating is rubbing against; For steel alloys, it is about 0.6.
As far as biocompatibility is concerned, TiN doesn’t react with blood, bones, tissues, and bodily fluids, which makes it suitable for medical, dental, and food applications.
Titanium nitride has a wide range of applications:
- As a precursor for wear-resistant and decorative “gold-like” coating
- As a material for crucibles for the anoxic casting of metals
- As a component in specialized refractories and cermets
Because of its incredible wear resistance, heat resistance, corrosion resistance, and high hardness, TiN coating has thousands of applications. It is usually deposited by chemical vapor deposition and physical vapor deposition evaporation.
TiN coating can be applied to all kinds of tools, including taps, drills, reamers, end mills, dovetails, and punching and forming tools. It works on many different materials such as T15, M2, M4, high-speed steel, stainless steel, carbide, and other materials.
The coating significantly improves tools’ life by up to 7 times over uncoated tools. It improves lubricity, reduces friction, and minimizes galling between sliding mold components.
It is also employed to coat gold jewelry, forks of motorcycles and bicycles, and automobile trims (for decoration purposes).
TiN is not as good a conductor as a metal, but it has a tendency to conduct electricity. Unlike most metals, it cannot be diffused into the silicon microchip. Thus, a thin layer of titanium nitride (between a metal contact and the silicon) acts as a barrier preventing the chip from being damaged while still allowing the current to pass through.
Some studies show that TiN can be used to make high-performance anodes for lithium-ion batteries. TiN-coated silicon nanoparticles look promising for this role. The material exhibits stable performance and excellent efficiency for a large number of charge-discharge cycles.
Knee prosthesis with the golden color titanium-nitride coating | Source: MDPI
Due to the excellent hemocompatibility and intrinsic biocompatibility, TiN films are also applied to medical instruments, such as metals for hip joint, heart valve replacements, and dental prosthesis. Tin layers are fabricated on the surface of titanium implants to improve their corrosion and wear resistance.
Market Size of Titanium Nitride Coating
According to Emergen Research, the TiN coating market is expected to reach $8.29 billion by 2018, registering a compound annual growth rate of 8% from 2021 to 2028.
This revenue growth is supported robustly by increasing demand for injection molding equipment, high-quality tools, and numerous end-use industries like chemicals, printing, and automobile. TiN market growth also depends a lot on the increasing requirement of corrosion-resistant coatings and materials for developing surgical devices and food processing equipment.
However, non-uniform pricing of TiN coatings, as well as the availability of alternative coating techniques, can restrain the growth during the forecast period.
In 2020, Asia Pacific dominated the global TiN coating market with a share of 26.3%. Japan and China are the most prominent countries of this market owing to the domestic policies, technological advancements, and large investments for dedicated R&D facilities.
Africa and the Middle East are also expected to expand at a substantial growth rate over the forecast period due to the increase in industrial activity and research within this region.
Frequently Asked Questions
How is thin titanium nitride film created?
The two most commonly used techniques for creating thin layers of TiN are:
- Physical vapor deposition
- Chemical vapor deposition
In both techniques, pure titanium is sublime and exposed to nitrogen under vacuum.
Is it durable?
The TiN coating has enough hardness and temperature durability that it may effectively resist abrasion and reduce overall wear. It can improve the material life by up to 7 times over uncoated material.
How much does TiN coating cost?
A small tool (let’s say a pocket knife) could cost anywhere between $2 and $200, depending on the coating thickness and size and type of substrate material. If it is a 5 cm 303 stainless steel, the total coating cost would be $20.
Is titanium nitride magnetic?
Although bulk titanium nitride shows no evidence of magnetism, TiN nanostructures obtained via defect engineering possess both evident dynamic permeability and static ferromagnetic properties. Researchers believe that the composition and microstructure defects have profound effects on electromagnetic characteristics.
Is TiN coating safe for the human body?
Several studies conclude that the biocompatibility of titanium nitride coating is good — it doesn’t have any negative effects. Very thin layers of TiN (10-100 nanometers), as used to coat join implants, result in better adhesion of human fat cells to these layers.