Development of the hottest cemented carbide coated

Development of cemented carbide coated tools

hard coating of cemented carbide tools can improve tool life and productivity. Chemical vapor deposition (CVD) technology has developed from a single coating in the early days to a multi coating composed of tic, tin, TiCN and Al2O3. By selecting the coating sequence and the total thickness of the coating, it can meet the requirements of special metal cutting. In particular, Al2O3 coating can provide excellent high-temperature properties, including high diffusion wear resistance, excellent oxidation resistance and high thermal hardness, Therefore, it is widely used in high-speed machining of cast iron and steel

in recent years, tool manufacturers have introduced medium temperature (MT) CVD TiCN coating. When acetonitrile is used as an organic c/n source, TiCN deposition occurs at about 850 ℃, while high temperature CVD TiCN coating needs to be heated higher than 1000 ℃. MT TiCN coating has good wear resistance when used in turning and milling. It has a stable c/n ratio and can reduce the interface shape between the coating and cemented carbide matrix. 2 Adjust the tensile speed to the specified value to form ETA phase

more than ten years ago, physical vapor deposition (PVD) has been applied to cylindrical cemented carbide tools, including intermittent cutting and/or some metal cutting blades requiring sharp blades. At first, PVD coating was limited to tin, but now there are applicable PVD TiCN and TiAlN coatings in industry, using a variety of different PVD technologies, such as electron beam evaporation, sputtering, arc evaporation, etc

cvd diamond coating adopts many diamond synthesis techniques, the most common of which are hot wire method, microwave plasma method and D, C plasma jet method. Diamond coated cemented carbide tools have been produced by improving the coating method and coating bonding, and play an important role in processing non-ferrous and non-metallic materials. Recently, diamond coated cutting tools have been applied in industry

hard coating of cemented carbide tools

performance of hard coating

the success of hard coating of cutting tool matrix is due to the composite effect of physical and mechanical properties of the coating. From the perspective of application, the coating should have stable chemical stability, thermal hardness and strong adhesion with the substrate in the coming year. The optimized coating thickness, fine microstructure and residual compressive stress can further improve the coating performance

chemical stability

the standard of chemical inertia of coating materials is its formation standard. The negative number of free energy is very high or its solubility in workpiece materials is very low at cutting temperature. So far, CVD Al2O3 hard coating can fully meet these requirements in material processing. Amorphous PVD Al2O3 coating is soft and unstable, so it is not as good as crystalline CVD Al2O3; PVD TiAlN coating has higher stability than tin or TiCN, so it may be applied in high-speed machining. Diamond coated tools are suitable for processing non-ferrous alloys containing second phase abrasive particles (such as silicon aluminum alloys) and non-metallic materials that do not react with sulfur (such as metal matrix composites and fiber reinforced plastics)

hardness

the back of the cutting tool is subjected to abrasive wear. At the cutting temperature, as long as the hardness of the hard coating is higher than that of the substrate, it will help to enhance the anti abrasive wear. Although the cutting is mainly controlled by chemical wear, the high coating hardness will enhance the anti crescent wear performance of the front of the tool at a higher temperature. This view is still controversial

microstructure and morphology

coating methods and process parameters affect the microstructure of hard coatings. On the contrary, microstructure (such as particle size, particle structure, particle boundary and phase boundary) affects the mechanical properties and metal cutting properties of hard coatings. As we all know, PVD tin coating has fine particle size and higher microhardness than CVD TiN coating. PVD coating with high lattice defect density also has high residual stress, which also helps to improve its microhardness

Al2O3 coating of cemented carbide tools is usually deposited by CVD. Al2O3 has many crystalline forms; The most common polycrystalline form is stable α－ Al2O3 and metastable k-al2o3. α－ The particle shape of Al2O3 is columnar. Compared with k-al2o3, its dislocation density and pores are larger, and pores often exist at the particle boundary. K-al2o3 coating is 2 ~ 0.5 of fine particles μ m. And there are no dislocations

bonding

in order to obtain satisfactory cutting performance, the bonding between the tool coating and the substrate must be firm. The nucleation of the coating on the substrate should be the mutual diffusion of the coating and the substrate atoms at the interface, which can be achieved in the thermal CVD method. The plasma assisted deposition method can improve the rapid diffusion of the coating sample at the interface even if the lattice defects are produced by high-energy bombardment at a low temperature. For the diamond coating, before the coating, the cobalt on the surface of the substrate to be coated is the key to measure the bonding strength between the coating and the substrate, Surface corrosion and heat treatment are another method to promote the adhesion of diamond film to cemented carbide matrix

coating thickness

in order to achieve the maximum metal removal rate, the thickness of the coating must be optimized: it is too thin and the holding time during cutting is too short; If it is too thick, its function is like an integral material, losing the superiority of its combination with the matrix. It is determined that the coating thickness of new cutting tools ranges from 2 to 20 μ m。 The coating thickness of CVD deposition depends on the application, which is generally 5 ~ 20 μ M, and the PVD coating thickness is usually less than 5 μ m。 The thickness of diamond coating is generally thicker than CVD or PVD coating, and it can be applied to the thickness of 20 ~ 40 as polycrystalline diamond coating μ The range of M

deposition methods of hard coatings

according to the energy form required by the volatilization and reaction of its raw materials, there are thermal deposition and plasma assisted deposition

nowadays, titanium based hard coatings tin, TiCN, tic, TiAlN and ceramic hard coatings Al2O3 are widely used in metal cutting tools. Many different thermal deposition and plasma deposition technologies are used to produce coatings with the same composition. In most cases, several different coating methods can be used. The microstructure of the coating and the performance of the coated tool are determined by the coating method and the coating process parameters. Generally, the evaporation form and deposition temperature can distinguish different coating methods. Hot high temperature CVD (ht-cvd) occurs at 900 ~ 1100 ℃, which is higher than 300 ~ 600 ℃ adopted by PVD

the working temperature of hot medium temperature CVD (mt-cvd) method is between ht-cvd and PVD methods. When acetonitrile (CH3CN) is used as an organic c/n source to deposit MT TiCN coating, the temperature of mt-cvd coating is reduced to 750 ~ 900 ℃. It is possible to further reduce the deposition temperature to below 750 ℃ with plasma assisted CVD hard coating. In pa-cvd process, using pulsed low-voltage glow discharge to catalyze the reaction gas can make the chemical reaction take place at a lower temperature. Unlike CVD method, the deposition temperature of PVD method is quite low, so the PVD plasma produces a metastable structure. The negative bias voltage is used to introduce ion bombardment on the substrate, which improves the adhesion of PVD coating and grows a fine-grained wear-resistant layer. Intense ion bombardment also introduces high internal stress in PVD coating

due to different volatilization forms of metallic hard components, their PVD methods and plasma conditions are also different

pvd sputtering method is that the metal vapor volatilizes directly from the metal target without passing through the liquid phase. Its main advantage is that it can evaporate metals with different melting points (such as TiAlN). The input energy of PVD arc evaporation method is higher than that of PVD sputtering method. The high-energy arc quickly passes through the volatile metal surface, making a small and limited area volatile. The plasma produced in this way is composed of highly ionized metal vapor

at present, there are three methods for diamond deposition: microwave plasma method, hot wire method and plasma jet method. A large number of hydrogen atoms should be present in high-quality diamond films to stabilize SP3 diamond bonds and reduce the amount of graphite in the films

microwave plasma method uses microwave energy to produce a deposition rate of 2 ~ 3 μ M/h glow discharge. The hot wire method is to heat the refractory wire to 2000 ~ 2500 ℃ to produce enough atomic hydrogen and diamond original particles, and the deposition rate can reach 0.5 ~ 1.5 μ m/h。 Plasma jet method includes D, C, R and f plasma, and their gas temperature is in the range of 5000 ~ 8000 ℃. Thermal plasma promotes the decomposition of gas particles, which can reach a very high deposition rate (as high as 400 μ m/h)。

all the above thermal and plasma assisted coating methods require expensive equipment. In addition, the complexity of the coating process (technical or economic reasons) makes it difficult to combine different coating methods

coating technology is basically divided into two important process parameters: deposition temperature and working pressure. These parameters have a great impact on deposition conditions and the performance of coated products

because coated tools have the properties of anti abrasive wear and anti crescent wear, and allow the use of high cutting speed, more than 60% of metal cutting blades in the United States and Western Europe are CVD coated. The brittleness of cemented carbide matrix is formed by early CVD coating deposition technology η Now, due to the better carbon control of the matrix and the improvement of CVD method, it is formed η The condition of phase has been greatly reduced or eliminated, making the application range of coated cemented carbide tools wider, including turning, boring, wire cutting, grooving, cutting and milling. These cutters are suitable for processing sulfur, alloy, stainless steel, gray cast iron, ductile cast iron and superalloy materials

5 for anti-wear of milling process μ M ht-cvd coating, the first layer is tin, which can reduce the formation η The tendency of phase; Coating for turning, the first layer is 13 μ M thick TiC (ht-cvd). The main action layer growing on the first layer is TiCN, which optimizes the hardness, anti crescent wear and anti rear wear performance. The surface layer is tin

especially for the application of intermittent cutting (milling), the toughness of CVD coated cemented carbide tools can be further improved by using mt-cvd coating. The lower deposition temperature (~ 850 ℃) and shorter deposition time of mt-cvd method reduce the formation of brittleness at the interface between coating and substrate η Therefore, the performance of coated tools in intermittent cutting applications is improved. The higher deposition rate of mt-cvd method produces a columnar coating structure. Mt-cvd coating can be applied to all machining fields where ht-cvd coating is combined with the above conditions

cvd Al2O3 coating method has also been greatly improved, which can produce a certain crystal structure, thick and uniform Al2O3 coating. Due to the high temperature performance of Al2O3, ht-al2o3 coated tools can be applied to high-speed machining steel and cast iron. Al2O3 coating can be deposited as a single layer or alternating layers α- With Al2O3 or k-al2o3 structure, these coatings can almost achieve the same high cutting speed as ceramic cutting tools

at present, both Al2O3 coating with excellent high temperature performance and mt-cvd TiCN coating with high toughness have been developed. These mt-ticn-al2o3 composite coatings have been successfully used in milling and turning, and k-al2o3 and α- Al2O3。

progress of PVD coating

because PVD method has the advantages of low deposition temperature, smooth, fine particle crack free coating on sharp blade and good residual internal stress, PVD tin coating has been widely used in cemented carbide tools and its supporting express enterprises to carry out the pilot of "ecological (green) design of industrial products" (such as metal ceramic matrix sensitive to coating temperature)

the progress of PVD technology has led to the new commercialization