Coating technology, together with materials and cutting processes, is called the three key technologies in the field of cutting tool manufacturing. From the first CVDTiN/TiC/TiCN adopted in 1970 to the PVD coating technology that began in 1980, modern coating technology is now widely used in tools, molds, parts and decorative products. The coating technology can effectively improve the service life of the cutting tool, and the tool can obtain excellent comprehensive mechanical properties, thereby greatly improving the machining efficiency.
Coated tools have developed the fastest new tools in recent decades. At present, coated tools in industrialized countries have accounted for more than 80%, and more than 90% of cutting tools used on CNC machines have coated tools. Due to factors such as understanding problems and prices, China's tool coating technology still has a big gap compared with industrial developed countries. The number of coated tools is also far away, accounting for only 20% of all tools. Among them, CNC machine tools and It is much more used on machining centers, and it is less pitiful on ordinary non-CNC machines.
Coating tool features
The coated tool combines the high hardness and high toughness of the substrate with high hardness and high wear resistance, which improves the wear resistance of the tool without reducing its toughness. The coating tool has a wide versatility and a wide range of processing, and the use of coated tools can achieve significant economic benefits. A coated tool can be used in place of several non-coated tools, which greatly reduces tool inventory, simplifies tool management, and reduces tooling costs. However, after the coating process of the existing coating process, the material properties of the coating material of the base material are different, the internal stress of the coating residue is large, the interface bonding strength between the coating substrates is low, the coating is easy to peel off, and the coating process is still The disadvantages are that the strength of the substrate is lowered, the resharpability of the coating blade is poor, the coating equipment is complicated, expensive, the process requirements are high, the coating time is long, and the tool cost is increased.
Common coating materials and properties
Common coating materials
Common coating materials include carbide, nitride, carbonitride, oxide, boride, silicide, diamond and composite coatings in dozens of categories. These coating materials can be classified into metal bond type and covalent bond type ion bond type according to the chemical bond characteristics.
Coating material properties
Metal bond coating materials (such as TiB2, TiC, TiN, VC, WC, etc.) have high melting point, low brittleness, high interface bonding strength, strong interaction tendency, good multi-layer matching, good comprehensive performance, and most common coatings. material. The covalent bond type coating materials (such as B4C, SiC, BN, diamond, etc.) have high hardness, low coefficient of thermal expansion, poor bonding strength with the interface of the substrate, and poor stability of multilayer adhesion. The ion-bonded material has good chemical stability, large brittleness, large thermal expansion coefficient, low melting point and low hardness.
These coating materials use up to TiC, TiN, Al2O3, diamond and composite coatings.
TiC has good wear resistance and can effectively improve the anti-crater wear resistance of the tool. It is suitable for low speed cutting and wear. TiN coating has low friction coefficient, good lubrication performance, can reduce cutting hot cutting force, and is suitable for generating fusion wear. Cutting; Al2O3 high temperature wear resistance, heat resistance and oxidation resistance better than TiCTiN, low crater wear rate, suitable for high speed, large cutting hot cutting; diamond coating hardness, high thermal conductivity, low friction coefficient, suitable for colored Metal alloys are cut at high speed; while composite coatings combine several coating materials, they are currently dominated by a two-coat, three-coat combination.
Common coating method
Currently, coating methods such as CVD (Chemical Vapor Deposition) PVD (Physical Vapor Deposition) are commonly used, and other methods such as plasma spraying, flame spraying, electroplating, and dissolved salt electrolysis have significant application limitations.
The CVD method utilizes metal halide vapors, other chemical components of hydrogen, and a gas-solid reaction such as decomposition, heat-sealing, or chemical transfer to heat the surface of the substrate to form a solid deposited layer at a high temperature of 950 to 1050 °C. The CVD process has high requirements, and the chlorine corrosion and hydrogen embrittlement deformation may cause the coating to be easily broken and the strength of the substrate section to decrease. When the cemented carbide is coated, the decarburization phenomenon is easily formed to form the n phase. In recent years, the low temperature CVD PCVD method has been successfully developed to improve the original CVD process.
The PVD method starts late, develops fast, and has a low temperature (about 300~500 °C). The advantages are many, but the coating uniformity is not as good as the CVD method. The coating and the substrate are not firmly bonded, the coating hardness is relatively low, and the coating superiority is not. Fully reflected. The PVD process requires higher process than the CVD process, the equipment is more complex, and the coating cycle is long.
At present, the commonly used PVD methods include low pressure electron beam evaporation (LVEE), cathode electron arc deposition (CAD), triode high voltage electron beam evaporation (THVEE), unbalanced magnetron sputtering (UMS), and ion beam assisted deposition ( IAD) Dynamics ion beam mixing (DIM), which differs mainly from the deposition material vaporization method and the plasma generation method, so that the film formation speed film quality is different.
Coating tool development direction
1 new coating material
There are many new types of tool coating materials: TiCN-based new coatings and TiCTiN coatings have good toughness and hardness, which is 2 to 4 times more durable than conventional TiN tools. In addition, new coating materials such as (Ti, Zr)CN, (Ti, Al)CN, (Ti, Si)CN, etc., which are based on TiCN, have appeared. AlON coated tools produce minimal crater wear. TiAlN has high temperature hardness and excellent oxidation resistance. It has high hardness and good oxidation resistance. Its cutting performance is better than TiN coating. The tool life can be increased by 1~4 times when it is used to process aerospace alloy materials. The CrCCrN coating has no titanium coating and can effectively cut titanium, titanium and other soft materials such as aluminum alloy. In addition, Hf, Zr, Ta carbide and nitride, Hf, Zr, Ti, N, Ta boride, Hf, Zr, Ti, Be oxide and other coating materials have been successfully used.
The titanium aluminum nitride coating is also converted from Ti0.75Al0.25N to Ti0.5Al0.5N. The oxidation temperature of Ti0.5Al0.5N coating is 700 °C, and an amorphous layer is formed on the surface by air heating. The Al2O3 film protects the coating.
A Japanese company has developed a new coating called SG, which consists of three layers of TiN, TiCN and Ti film. Its wear resistance is better than that of TiN coating, and the coating has high bonding strength with the substrate. The surface layer is Ti-based. The film layer has excellent heat resistance.
Switzerland has also developed a new process called “MOVIC†soft coating, which is coated with a solid lubricating film molybdenum disulfide on the surface of the tool. The cutting life of the tool is increased several times and an excellent machined surface can be obtained. Other chalcogen elements such as soft coatings such as WS2 have also made some progress. These soft coatings have good application prospects in processing high-strength aluminum alloy precious metals.
In recent years, high hardness coatings have begun to appear. Including cubic boron nitride (CBN) coating, carbon nitride (CNX), polycrystalline nitride superlattice coating, and the like. CBN coating hardness of 5200kgf / mm2, second only to diamond, can effectively cut other hard-to-machined alloys of hardened steel. If a carbon nitride (CNX) coating is capable of forming b-C3N4, it is theoretically possible to calculate that the hardness will exceed that of diamond. There have been reports of carbon nitride synthesis. Polycrystalline Nitride Superlattice Coating is a promising new tool coating. The hardness of polycrystalline TiN/NbNTiN/VN superlattice coating is 5200kgf/mm25600kgf/mm2, respectively. The superlattice coating is due to layer or layer. Difficulty in dislocations leads to high hardness.
Coating process
With the development of coating technology, a comprehensive PVDCVDPACVD method has emerged. In addition, there is an ion beam sputtering method. The ion beam assisted deposition technique (IBAD) can also be used for coating. The ion beam assisted deposition combines the advantages of vapor deposition and ion implantation. . Plasma-assisted chemical vapor deposition (PCVD) uses plasma to promote chemical reactions, which can reduce the deposition temperature to 200-500 °C. The Sol-Gel method has received more and more attention because of its own advantages.
MT-CVD (Warm Chemical Vapor Deposition) overcomes the shortcomings of general HD-CVD (high temperature chemical vapor deposition) to a certain extent, its deposition temperature is low (700 ~ 900 ° C), deposition speed is fast, coating thickness is thick, process ring plating Well, for the complex workpiece with uniform coating, and the coating adhesion is high, the residual stress inside the coating is small, which is better than the HT-CVD coating process.
The range of substrates used for coatings has also expanded, including high speed steels and hard alloy ceramics. In recent years, ceramic coated cemented carbide tools have developed rapidly. In particular, Al2O3 ceramics are particularly suitable for high-speed cutting due to their high chemical stability and oxidation resistance. Ceramic coatings account for a large proportion.
Although the tool coating process has achieved considerable development and special gradient coating processes, overall coating technology needs to be further improved.
The coated tool better solves the contradiction between the strength and toughness of the tool and greatly improves the cutting speed of the tool durability. However, the coating is easy to peel off, and the process is complicated and expensive. Tool coating materials use up to TiC, TiN, Al2O3, diamond and composite coatings. Common coating method CVD method PVD method. New coating materials and new coating methods continue to emerge. Special new high-hard coatings and soft-coating materials will make coating tools more and more widely used.
Coated tools have developed the fastest new tools in recent decades. At present, coated tools in industrialized countries have accounted for more than 80%, and more than 90% of cutting tools used on CNC machines have coated tools. Due to factors such as understanding problems and prices, China's tool coating technology still has a big gap compared with industrial developed countries. The number of coated tools is also far away, accounting for only 20% of all tools. Among them, CNC machine tools and It is much more used on machining centers, and it is less pitiful on ordinary non-CNC machines.
Coating tool features
The coated tool combines the high hardness and high toughness of the substrate with high hardness and high wear resistance, which improves the wear resistance of the tool without reducing its toughness. The coating tool has a wide versatility and a wide range of processing, and the use of coated tools can achieve significant economic benefits. A coated tool can be used in place of several non-coated tools, which greatly reduces tool inventory, simplifies tool management, and reduces tooling costs. However, after the coating process of the existing coating process, the material properties of the coating material of the base material are different, the internal stress of the coating residue is large, the interface bonding strength between the coating substrates is low, the coating is easy to peel off, and the coating process is still The disadvantages are that the strength of the substrate is lowered, the resharpability of the coating blade is poor, the coating equipment is complicated, expensive, the process requirements are high, the coating time is long, and the tool cost is increased.
Common coating materials and properties
Common coating materials
Common coating materials include carbide, nitride, carbonitride, oxide, boride, silicide, diamond and composite coatings in dozens of categories. These coating materials can be classified into metal bond type and covalent bond type ion bond type according to the chemical bond characteristics.
Coating material properties
Metal bond coating materials (such as TiB2, TiC, TiN, VC, WC, etc.) have high melting point, low brittleness, high interface bonding strength, strong interaction tendency, good multi-layer matching, good comprehensive performance, and most common coatings. material. The covalent bond type coating materials (such as B4C, SiC, BN, diamond, etc.) have high hardness, low coefficient of thermal expansion, poor bonding strength with the interface of the substrate, and poor stability of multilayer adhesion. The ion-bonded material has good chemical stability, large brittleness, large thermal expansion coefficient, low melting point and low hardness.
These coating materials use up to TiC, TiN, Al2O3, diamond and composite coatings.
TiC has good wear resistance and can effectively improve the anti-crater wear resistance of the tool. It is suitable for low speed cutting and wear. TiN coating has low friction coefficient, good lubrication performance, can reduce cutting hot cutting force, and is suitable for generating fusion wear. Cutting; Al2O3 high temperature wear resistance, heat resistance and oxidation resistance better than TiCTiN, low crater wear rate, suitable for high speed, large cutting hot cutting; diamond coating hardness, high thermal conductivity, low friction coefficient, suitable for colored Metal alloys are cut at high speed; while composite coatings combine several coating materials, they are currently dominated by a two-coat, three-coat combination.
Common coating method
Currently, coating methods such as CVD (Chemical Vapor Deposition) PVD (Physical Vapor Deposition) are commonly used, and other methods such as plasma spraying, flame spraying, electroplating, and dissolved salt electrolysis have significant application limitations.
The CVD method utilizes metal halide vapors, other chemical components of hydrogen, and a gas-solid reaction such as decomposition, heat-sealing, or chemical transfer to heat the surface of the substrate to form a solid deposited layer at a high temperature of 950 to 1050 °C. The CVD process has high requirements, and the chlorine corrosion and hydrogen embrittlement deformation may cause the coating to be easily broken and the strength of the substrate section to decrease. When the cemented carbide is coated, the decarburization phenomenon is easily formed to form the n phase. In recent years, the low temperature CVD PCVD method has been successfully developed to improve the original CVD process.
The PVD method starts late, develops fast, and has a low temperature (about 300~500 °C). The advantages are many, but the coating uniformity is not as good as the CVD method. The coating and the substrate are not firmly bonded, the coating hardness is relatively low, and the coating superiority is not. Fully reflected. The PVD process requires higher process than the CVD process, the equipment is more complex, and the coating cycle is long.
At present, the commonly used PVD methods include low pressure electron beam evaporation (LVEE), cathode electron arc deposition (CAD), triode high voltage electron beam evaporation (THVEE), unbalanced magnetron sputtering (UMS), and ion beam assisted deposition ( IAD) Dynamics ion beam mixing (DIM), which differs mainly from the deposition material vaporization method and the plasma generation method, so that the film formation speed film quality is different.
Coating tool development direction
1 new coating material
There are many new types of tool coating materials: TiCN-based new coatings and TiCTiN coatings have good toughness and hardness, which is 2 to 4 times more durable than conventional TiN tools. In addition, new coating materials such as (Ti, Zr)CN, (Ti, Al)CN, (Ti, Si)CN, etc., which are based on TiCN, have appeared. AlON coated tools produce minimal crater wear. TiAlN has high temperature hardness and excellent oxidation resistance. It has high hardness and good oxidation resistance. Its cutting performance is better than TiN coating. The tool life can be increased by 1~4 times when it is used to process aerospace alloy materials. The CrCCrN coating has no titanium coating and can effectively cut titanium, titanium and other soft materials such as aluminum alloy. In addition, Hf, Zr, Ta carbide and nitride, Hf, Zr, Ti, N, Ta boride, Hf, Zr, Ti, Be oxide and other coating materials have been successfully used.
The titanium aluminum nitride coating is also converted from Ti0.75Al0.25N to Ti0.5Al0.5N. The oxidation temperature of Ti0.5Al0.5N coating is 700 °C, and an amorphous layer is formed on the surface by air heating. The Al2O3 film protects the coating.
A Japanese company has developed a new coating called SG, which consists of three layers of TiN, TiCN and Ti film. Its wear resistance is better than that of TiN coating, and the coating has high bonding strength with the substrate. The surface layer is Ti-based. The film layer has excellent heat resistance.
Switzerland has also developed a new process called “MOVIC†soft coating, which is coated with a solid lubricating film molybdenum disulfide on the surface of the tool. The cutting life of the tool is increased several times and an excellent machined surface can be obtained. Other chalcogen elements such as soft coatings such as WS2 have also made some progress. These soft coatings have good application prospects in processing high-strength aluminum alloy precious metals.
In recent years, high hardness coatings have begun to appear. Including cubic boron nitride (CBN) coating, carbon nitride (CNX), polycrystalline nitride superlattice coating, and the like. CBN coating hardness of 5200kgf / mm2, second only to diamond, can effectively cut other hard-to-machined alloys of hardened steel. If a carbon nitride (CNX) coating is capable of forming b-C3N4, it is theoretically possible to calculate that the hardness will exceed that of diamond. There have been reports of carbon nitride synthesis. Polycrystalline Nitride Superlattice Coating is a promising new tool coating. The hardness of polycrystalline TiN/NbNTiN/VN superlattice coating is 5200kgf/mm25600kgf/mm2, respectively. The superlattice coating is due to layer or layer. Difficulty in dislocations leads to high hardness.
Coating process
With the development of coating technology, a comprehensive PVDCVDPACVD method has emerged. In addition, there is an ion beam sputtering method. The ion beam assisted deposition technique (IBAD) can also be used for coating. The ion beam assisted deposition combines the advantages of vapor deposition and ion implantation. . Plasma-assisted chemical vapor deposition (PCVD) uses plasma to promote chemical reactions, which can reduce the deposition temperature to 200-500 °C. The Sol-Gel method has received more and more attention because of its own advantages.
MT-CVD (Warm Chemical Vapor Deposition) overcomes the shortcomings of general HD-CVD (high temperature chemical vapor deposition) to a certain extent, its deposition temperature is low (700 ~ 900 ° C), deposition speed is fast, coating thickness is thick, process ring plating Well, for the complex workpiece with uniform coating, and the coating adhesion is high, the residual stress inside the coating is small, which is better than the HT-CVD coating process.
The range of substrates used for coatings has also expanded, including high speed steels and hard alloy ceramics. In recent years, ceramic coated cemented carbide tools have developed rapidly. In particular, Al2O3 ceramics are particularly suitable for high-speed cutting due to their high chemical stability and oxidation resistance. Ceramic coatings account for a large proportion.
Although the tool coating process has achieved considerable development and special gradient coating processes, overall coating technology needs to be further improved.
The coated tool better solves the contradiction between the strength and toughness of the tool and greatly improves the cutting speed of the tool durability. However, the coating is easy to peel off, and the process is complicated and expensive. Tool coating materials use up to TiC, TiN, Al2O3, diamond and composite coatings. Common coating method CVD method PVD method. New coating materials and new coating methods continue to emerge. Special new high-hard coatings and soft-coating materials will make coating tools more and more widely used.
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