Conventional transition group metal nitride coatings, such as TiN, CrN, etc. have long been widely used, but the modern actual processing conditions of the increasingly harsh and higher cutting accuracy requirements make them unable to meet, so the successive development of a diversified composition, functional diversification of the coating. New coatings have higher hardness and high-temperature oxidation resistance than conventional coatings, and have become an important direction for the development of today's coatings.

Conventional coating

(1) titanium nitride (TiN) coating: TiN is the use of PVD technology to prepare one of the most common coatings, not only can improve tool hardness, toughness, service life, but also a higher oxidation temperature, the coating is relatively certain corrosion, oxidation and abrasion resistance, so it is applied to high-speed steel cutting tools or forming tools can be obtained a good machining quality.

(2) titanium carbide (TiC) coating: TiC coating is the coating technology was first developed in the early stages of a single coating, coating the hardness than TiN high, strong mechanical wear properties and matrix bonding, in the cutting process can reduce the processing resistance and cutting temperature, the disadvantage is that the coating is brittle, toughness, bending strength is lower, suitable for tools to produce intense wear and continuous cutting occasions.

(3) titanium carbide nitride (TiCN) coating: TiCN coating is added by the TiN coating alloying element C, TiN lattice in part of the nitrogen atoms replaced by carbon atoms and the formation of both TiN and TiC advantages and features of the ternary coating. TiCN in the tribological application of the wear mechanism to be better than TiN, this is because of the existence of TiCN coating C as a lubricant reduces frictional wear. However, the coating fails at temperatures above 400°C, making TiCN coatings suitable for use on HSS tools with operating temperatures below 400°C. The TiCN coating is also suitable for use on HSS tools with operating temperatures below 400°C.


(4) Titanium Aluminium Nitrogen (TiAlN) coating: TiAlN/AlTiN coating is a composite coating with cubic NaCl structure formed by replacing Ti with Al in the basic TiN structure. The presence of aluminium oxide in the coating reduces the thermal conductivity of the film thereby improving the high temperature machining life of the tool. Due to the high hardness and wear resistance, as well as good thermal stability and age-hardening ability, is the most advanced machining process (eg: high-speed dry cutting) one of the first choice of wear-resistant materials. TiAlN than TiN-coated cutting tools have a high hardness, oxidation temperature, good red hardness, adhesion, low coefficient of thermal expansion and coefficient of friction. Cutting performance is better than TiN, can be applied to cast iron, stainless steel, high-temperature alloys of high-speed cutting or dry machining.

(5) Aluminium Titanium Nitrogen (AlTiN) coating: AITiN and TiAlN coatings are different in the proportion of aluminium and titanium, AlTiN coatings are widely used in the field of excellent mechanical and thermal properties of the wear-resistant, which is largely attributed to the increase in aluminium content. Compared to TiN coatings, AITiN coatings act as a protective layer for tools, reducing the amount of wear and fracture caused by larger impact cycles. Due to grain refinement after the organisational structure is more dense, AlTiN coating than TiAlN coating hardness is higher, while both the TiAlN coating excellent comprehensive mechanical properties, is an ideal coating for high-speed machining under the type of coating.

(6) chromium nitride (CrN) coating: CrN coating based on high hardness, high thermal stability, anti-wear and corrosion resistance, is a popular low-friction coating, very high deformation surface and large grain size of the CrN structure can be provided for the lubricant micro-storage, so that the CrN coating is also suitable for lubrication under the conditions of the work of the parts. In addition, good anti-bonding properties make CrN tool coatings the coating of choice for machining soft materials such as titanium alloys and aluminium, which are prone to chip-rule build-up and for cutting titanium alloys. This almost invisible CrN coating coated in high-speed steel, carbide materials, turning tools, milling cutters, forming tools, can greatly improve the machining performance of the tool, therefore, in the engineering has been widely used.