Keywords:
1. CVD diamond film coating tool substrate pretreatment technology Ideal tool material should have excellent wear resistance to extend tool life; high fracture toughness to withstand high cutting forces. However, most tool materials with good fracture toughness (such as high-speed steel) usually do not have good wear resistance, while materials with good wear resistance (such as ceramic materials) tend to have poor fracture toughness. Because of its good wear resistance and high fracture toughness, cemented carbide (WC-Co) materials are the substrate materials for CVD diamond film coating tools commonly used at home and abroad. However, due to the large difference in thermal expansion coefficients between diamond film and cemented carbide, the bond strength of the film base after deposition is poor, and the binder phase Co in the cemented carbide plays a role in promoting graphitization during the deposition process. Inhibition. In order to improve the deposition quality of the diamond film on the surface of the cemented carbide tool, the surface of the substrate must be properly pretreated (see Table 1 for the mechanical and thermal properties of the commonly used hard coating materials and substrates).
Table 1. Mechanical and Thermal Properties of Common Hard Coating Materials and Substrates - Melting Point or Decomposition Temperature (°C) - HV Hardness (MPa) - Young's Modulus (KN/mm2) - Thermal Expansion Coefficient (10-6/ K) - Thermal conductivity (W / mK)
Diamond-3800-80000-1050-1.3-1100
Cu-1084-/-98-16.6-386
Si-1420-/-/-2.5-84
WC-2776-23000-720-4.0-35
Al2O3-2047-21000-400-6.5-25
SiC-2760-26000-480-5.3-84
Si3N4-1900-17000-310-2.5-17
TiC-3067-28000-460-8.3-34
TiN-2950-21000-590-9.3-30
At present, the substrate surface pretreatment methods commonly used are: 1 surface de-Co treatment: etching of Co in the surface layer of the substrate by using HCl, HNO3, H2SO4, etc.; using hydrogen plasma or oxygen-containing hydrogen plasma engraving Corrosion Co; using chemical reagent passivation and other methods to make Co in the surface layer of the substrate inactive; replace Co with chemical reaction, put the cemented carbide substrate cutter into the chemical reagent, and replace the Co in the surface layer by displacement reaction Become other substances (such as Cu). 2 Pre-depositing an intermediate transition layer between the diamond film and the substrate. These transition layers should satisfy the requirements of moderate thermal expansion coefficient, stable chemical properties, good adhesion to cemented carbide and diamond, and reaction with Co to form stable compounds. . Currently, the transition layer materials commonly used are: Ti, B, TiC, TiN, Cu, etc.; composite transition layers: WC/W, TiN/TiCN/TiN, TiCN/Ti, and the like. Due to the existence of the intermediate transition layer, the internal stress caused by the lattice mismatch between the diamond film and the cemented carbide substrate and the difference in thermal expansion coefficient can be eliminated, and the carbon can be prevented from excessively penetrating into the substrate during the deposition process or Co can be deep from the substrate. The surface diffuses, thereby enhancing nucleation density and adhesion. 3 surface phytolith treatment. The surface of the cemented carbide substrate is sonicated with a suspension containing diamond micropowder (such as acetone) or the nano-sized diamond micropowder is evenly dispersed on the surface of the substrate by acetone, and then rapidly heated by a laser to embed the diamond micropowder into the surface layer of the binder phase. Can increase the nucleation density. In addition, surface chemical cleaning, liquid ultrasonic cleaning, and hydrogen plasma bombardment are also basic means of substrate pretreatment. R.Bichle et al found that when the Co content is in the range of 3% to 10%, the nucleation rate of the diamond film decreases with the increase of Co content; when the Co content exceeds 6%, the nucleation rate is the lowest. The results show that the proper two-step etching process, that is, the method of etching the WC phase with the Murakami agent and then removing the Co phase by acid etching has a good effect of removing Co.
2. What is the effect of diamond film structure on tool performance?
A number of research institutes at home and abroad have conducted research on the manufacture of simple indexable inserts using cemented carbide substrates and conducted turning tests. Studies have shown that the adhesion strength of diamond film coated tools decreases with increasing coating thickness. When the thickness of the coating is in the range of 5-10 μm, the adhesion strength decreases with the increase of the coating thickness when the coating thickness is in the range of 5-10 μm; when the coating thickness is After more than 10 μm, the adhesion strength decreases significantly as the thickness of the coating increases. Therefore, from the viewpoint of improving the adhesion strength, the coating thickness of the diamond thin film coating tool should not exceed 10 μm. It has also been reported that the diamond film prepared by the CVD method on the surface of the cemented carbide substrate is uneven, usually having a surface roughness of Ry 4 to 10 μm, and the surface shape of the cutting tool coated with the diamond film affects the processed aluminum alloy. The roughness of the surface makes it difficult to obtain the surface finish desired for finishing. Japan OSG Company has developed ultra-fine crystal diamond film cemented carbide tool, which has good anti-adhesion, high processing precision, durability and film toughness after cutting test. It has been widely used in diamond coating cutting developed by OSG. Tools are also favored by users. Sun Fanghong et al. used a hot-wire CVD method to grow a diamond film at the same time in the late deposition stage by increasing the carbon source concentration and lowering the reaction pressure. On the WC-Co6% cemented carbide (YG6), it grows in the early and middle stages of deposition. The surface of the layer is 10 to 15 μm thick with a smooth diamond film. The turning test shows that the service life and cutting performance of the coated tool are significantly improved.
The main wear and breakage effects of CVD diamond film coated tools for cutting high silicon aluminum alloys include abrasive wear, diamond film cracking and spalling. Abrasive wear is mainly caused by the "micro-cutting" effect of hard-point Si particles in the workpiece material. The early diamond film spalling is mainly due to insufficient bonding strength between the diamond film and the substrate, the depth of the decobalted layer is too large, and the strength of the matrix is ​​low. The cutting force and the thermal shock of cutting are the main reasons for the spalling of the diamond film in the middle and late stages. Different substrate materials have different adhesion strengths of diamond film coating tools. Intermittent cutting tests of tools prepared by flame method on W, WC-1.5%Co, WC-3%Co, WC-6%Co substrates show that: WC- The adhesion strength of the 1.5% Co matrix tool is higher, while the adhesion strength of the WC-3%Co and WC-6%Co matrix cutters is lower. The diamond film was deposited on the surface of cemented carbide and Si3N4 ceramic tool by hot wire CVD. The results show that the bonding strength of the deposited diamond film on Si3N4 ceramic is much higher than that of the diamond film on the cemented carbide, which is due to the easy surface of the cemented carbide. The loose layer of graphite, WC and the like are formed to reduce the bonding property of the film. The diamond film is easy to directly fail in the form of spalling; and the film-based interface of the Si3N4 ceramic substrate may form a SiC transition layer, which can significantly enhance the bonding strength of the film. However, under the action of compressive stress, the diamond film on the Si3N4 ceramic substrate will fail in the form of cracks and crack propagation.
3. Preparation of CVD diamond film coated drill bit Compared with ceramics, cemented carbide has better toughness and is easier to process into complex shaped tools, so it is used as the base material for the main deposited diamond film coated drill bit. Chen Ming, from Shanghai Jiaotong University, deposited diamond film on the cemented carbide YG6 drill bit. The drill diameters were φ2mm, φ3mm, φ4mm, φ6mm, and the workpiece material was SiC particle reinforced aluminum matrix composite (35Vol% SiC, 14μm). From 1400 to 9000 r/min, the diamond deposition equipment is EACVD, and the reaction gases are acetone and hydrogen. The substrate pretreatment is treated by oxidation, that is, the drill bit is placed in a microwave plasma device of a CO2 atmosphere to cause oxidation reaction of WC and Co elements on the surface of the tool substrate. The bond phase Co between the WC particles is rapidly oxidized due to different oxidation rates. With the removal of oxides (addition of alkali solution to remove the surface of the bit and the oxide of Co), the WC particles on the surface of the tool substrate are exposed to the surface, thereby increasing the surface roughness, which is beneficial to the nucleation and initial stage of the diamond. Growing. The cutting test shows that in the roughening treatment of the tool substrate surface, the oxidation treatment method is suitable for complex shape cutters, which can ensure the cutting edge is intact and is convenient for mass production. It is a promising tool substrate pretreatment method; In the process of CVD deposition of diamond, the addition of proper amount of adhesion promoter can significantly improve the adhesion of diamond film and improve the tool life. The CVD coating process is suitable for the preparation of complex shape diamond film coating tools with diameter of φ4mm and above.
4. What is the effect of tool geometry on the performance of diamond film coating tools?
The spalling of the diamond film is not only related to its adhesion strength on the tool substrate, but also to the geometry of the tool. The research shows that the radius of the tool tip is an important geometric parameter that affects the change of cutting force and the heat dissipation condition of the cutting zone. Under the condition of the tool base material, surface pretreatment, deposition process and coating thickness, the tool nose radius is cut. The peeling of the diamond film during the process has an important influence. The impact resistance of the diamond film coated tool increases with the increase of the radius of the tool nose arc. However, when the tool nose radius is greater than 1.5 mm, the impact resistance of the tool decreases. Under the condition that the cutting system has sufficient rigidity, appropriately increasing the radius of the cutting edge can effectively improve the impact resistance of the diamond film coated tool. Hanyu et al. studied diamond-coated drill bits for cutting high-silicon aluminum alloys. The results show that by changing the shape of the cutting edge and the thickness of the coating, the bit structure can be optimized to improve the cutting effect. During the rotation of the drill bit, the mechanical load acting on the blade decreases as the blade inclination increases, and at the same time the cutting load tends to concentrate on the tip of the blade as the blade inclination increases, which results in a coating Local stress concentration. Tests have shown that diamond coated drill bits show the best cutting results when the blade angle is 20°.
1. CVD diamond film coating tool substrate pretreatment technology Ideal tool material should have excellent wear resistance to extend tool life; high fracture toughness to withstand high cutting forces. However, most tool materials with good fracture toughness (such as high-speed steel) usually do not have good wear resistance, while materials with good wear resistance (such as ceramic materials) tend to have poor fracture toughness. Because of its good wear resistance and high fracture toughness, cemented carbide (WC-Co) materials are the substrate materials for CVD diamond film coating tools commonly used at home and abroad. However, due to the large difference in thermal expansion coefficients between diamond film and cemented carbide, the bond strength of the film base after deposition is poor, and the binder phase Co in the cemented carbide plays a role in promoting graphitization during the deposition process. Inhibition. In order to improve the deposition quality of the diamond film on the surface of the cemented carbide tool, the surface of the substrate must be properly pretreated (see Table 1 for the mechanical and thermal properties of the commonly used hard coating materials and substrates).
Table 1. Mechanical and Thermal Properties of Common Hard Coating Materials and Substrates - Melting Point or Decomposition Temperature (°C) - HV Hardness (MPa) - Young's Modulus (KN/mm2) - Thermal Expansion Coefficient (10-6/ K) - Thermal conductivity (W / mK)
Diamond-3800-80000-1050-1.3-1100
Cu-1084-/-98-16.6-386
Si-1420-/-/-2.5-84
WC-2776-23000-720-4.0-35
Al2O3-2047-21000-400-6.5-25
SiC-2760-26000-480-5.3-84
Si3N4-1900-17000-310-2.5-17
TiC-3067-28000-460-8.3-34
TiN-2950-21000-590-9.3-30
At present, the substrate surface pretreatment methods commonly used are: 1 surface de-Co treatment: etching of Co in the surface layer of the substrate by using HCl, HNO3, H2SO4, etc.; using hydrogen plasma or oxygen-containing hydrogen plasma engraving Corrosion Co; using chemical reagent passivation and other methods to make Co in the surface layer of the substrate inactive; replace Co with chemical reaction, put the cemented carbide substrate cutter into the chemical reagent, and replace the Co in the surface layer by displacement reaction Become other substances (such as Cu). 2 Pre-depositing an intermediate transition layer between the diamond film and the substrate. These transition layers should satisfy the requirements of moderate thermal expansion coefficient, stable chemical properties, good adhesion to cemented carbide and diamond, and reaction with Co to form stable compounds. . Currently, the transition layer materials commonly used are: Ti, B, TiC, TiN, Cu, etc.; composite transition layers: WC/W, TiN/TiCN/TiN, TiCN/Ti, and the like. Due to the existence of the intermediate transition layer, the internal stress caused by the lattice mismatch between the diamond film and the cemented carbide substrate and the difference in thermal expansion coefficient can be eliminated, and the carbon can be prevented from excessively penetrating into the substrate during the deposition process or Co can be deep from the substrate. The surface diffuses, thereby enhancing nucleation density and adhesion. 3 surface phytolith treatment. The surface of the cemented carbide substrate is sonicated with a suspension containing diamond micropowder (such as acetone) or the nano-sized diamond micropowder is evenly dispersed on the surface of the substrate by acetone, and then rapidly heated by a laser to embed the diamond micropowder into the surface layer of the binder phase. Can increase the nucleation density. In addition, surface chemical cleaning, liquid ultrasonic cleaning, and hydrogen plasma bombardment are also basic means of substrate pretreatment. R.Bichle et al found that when the Co content is in the range of 3% to 10%, the nucleation rate of the diamond film decreases with the increase of Co content; when the Co content exceeds 6%, the nucleation rate is the lowest. The results show that the proper two-step etching process, that is, the method of etching the WC phase with the Murakami agent and then removing the Co phase by acid etching has a good effect of removing Co.
2. What is the effect of diamond film structure on tool performance?
A number of research institutes at home and abroad have conducted research on the manufacture of simple indexable inserts using cemented carbide substrates and conducted turning tests. Studies have shown that the adhesion strength of diamond film coated tools decreases with increasing coating thickness. When the thickness of the coating is in the range of 5-10 μm, the adhesion strength decreases with the increase of the coating thickness when the coating thickness is in the range of 5-10 μm; when the coating thickness is After more than 10 μm, the adhesion strength decreases significantly as the thickness of the coating increases. Therefore, from the viewpoint of improving the adhesion strength, the coating thickness of the diamond thin film coating tool should not exceed 10 μm. It has also been reported that the diamond film prepared by the CVD method on the surface of the cemented carbide substrate is uneven, usually having a surface roughness of Ry 4 to 10 μm, and the surface shape of the cutting tool coated with the diamond film affects the processed aluminum alloy. The roughness of the surface makes it difficult to obtain the surface finish desired for finishing. Japan OSG Company has developed ultra-fine crystal diamond film cemented carbide tool, which has good anti-adhesion, high processing precision, durability and film toughness after cutting test. It has been widely used in diamond coating cutting developed by OSG. Tools are also favored by users. Sun Fanghong et al. used a hot-wire CVD method to grow a diamond film at the same time in the late deposition stage by increasing the carbon source concentration and lowering the reaction pressure. On the WC-Co6% cemented carbide (YG6), it grows in the early and middle stages of deposition. The surface of the layer is 10 to 15 μm thick with a smooth diamond film. The turning test shows that the service life and cutting performance of the coated tool are significantly improved.
The main wear and breakage effects of CVD diamond film coated tools for cutting high silicon aluminum alloys include abrasive wear, diamond film cracking and spalling. Abrasive wear is mainly caused by the "micro-cutting" effect of hard-point Si particles in the workpiece material. The early diamond film spalling is mainly due to insufficient bonding strength between the diamond film and the substrate, the depth of the decobalted layer is too large, and the strength of the matrix is ​​low. The cutting force and the thermal shock of cutting are the main reasons for the spalling of the diamond film in the middle and late stages. Different substrate materials have different adhesion strengths of diamond film coating tools. Intermittent cutting tests of tools prepared by flame method on W, WC-1.5%Co, WC-3%Co, WC-6%Co substrates show that: WC- The adhesion strength of the 1.5% Co matrix tool is higher, while the adhesion strength of the WC-3%Co and WC-6%Co matrix cutters is lower. The diamond film was deposited on the surface of cemented carbide and Si3N4 ceramic tool by hot wire CVD. The results show that the bonding strength of the deposited diamond film on Si3N4 ceramic is much higher than that of the diamond film on the cemented carbide, which is due to the easy surface of the cemented carbide. The loose layer of graphite, WC and the like are formed to reduce the bonding property of the film. The diamond film is easy to directly fail in the form of spalling; and the film-based interface of the Si3N4 ceramic substrate may form a SiC transition layer, which can significantly enhance the bonding strength of the film. However, under the action of compressive stress, the diamond film on the Si3N4 ceramic substrate will fail in the form of cracks and crack propagation.
3. Preparation of CVD diamond film coated drill bit Compared with ceramics, cemented carbide has better toughness and is easier to process into complex shaped tools, so it is used as the base material for the main deposited diamond film coated drill bit. Chen Ming, from Shanghai Jiaotong University, deposited diamond film on the cemented carbide YG6 drill bit. The drill diameters were φ2mm, φ3mm, φ4mm, φ6mm, and the workpiece material was SiC particle reinforced aluminum matrix composite (35Vol% SiC, 14μm). From 1400 to 9000 r/min, the diamond deposition equipment is EACVD, and the reaction gases are acetone and hydrogen. The substrate pretreatment is treated by oxidation, that is, the drill bit is placed in a microwave plasma device of a CO2 atmosphere to cause oxidation reaction of WC and Co elements on the surface of the tool substrate. The bond phase Co between the WC particles is rapidly oxidized due to different oxidation rates. With the removal of oxides (addition of alkali solution to remove the surface of the bit and the oxide of Co), the WC particles on the surface of the tool substrate are exposed to the surface, thereby increasing the surface roughness, which is beneficial to the nucleation and initial stage of the diamond. Growing. The cutting test shows that in the roughening treatment of the tool substrate surface, the oxidation treatment method is suitable for complex shape cutters, which can ensure the cutting edge is intact and is convenient for mass production. It is a promising tool substrate pretreatment method; In the process of CVD deposition of diamond, the addition of proper amount of adhesion promoter can significantly improve the adhesion of diamond film and improve the tool life. The CVD coating process is suitable for the preparation of complex shape diamond film coating tools with diameter of φ4mm and above.
4. What is the effect of tool geometry on the performance of diamond film coating tools?
The spalling of the diamond film is not only related to its adhesion strength on the tool substrate, but also to the geometry of the tool. The research shows that the radius of the tool tip is an important geometric parameter that affects the change of cutting force and the heat dissipation condition of the cutting zone. Under the condition of the tool base material, surface pretreatment, deposition process and coating thickness, the tool nose radius is cut. The peeling of the diamond film during the process has an important influence. The impact resistance of the diamond film coated tool increases with the increase of the radius of the tool nose arc. However, when the tool nose radius is greater than 1.5 mm, the impact resistance of the tool decreases. Under the condition that the cutting system has sufficient rigidity, appropriately increasing the radius of the cutting edge can effectively improve the impact resistance of the diamond film coated tool. Hanyu et al. studied diamond-coated drill bits for cutting high-silicon aluminum alloys. The results show that by changing the shape of the cutting edge and the thickness of the coating, the bit structure can be optimized to improve the cutting effect. During the rotation of the drill bit, the mechanical load acting on the blade decreases as the blade inclination increases, and at the same time the cutting load tends to concentrate on the tip of the blade as the blade inclination increases, which results in a coating Local stress concentration. Tests have shown that diamond coated drill bits show the best cutting results when the blade angle is 20°.
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