CVD diamond film coating tools Research Survey – Diamond – Machine Tool Industry
1. Introduction Diamond has excellent physical and chemical properties of all substances in nature, has the highest hardness, room temperature has the highest thermal conductivity, but also has very low thermal expansion coefficient, low friction coefficient, good chemical stability, large the band gap (5.5eV), high sound propagation speed, high doping of the semiconductor and light from the far-infrared to ultraviolet region of the optical zone permeability, so many excellent performance makes their machining, micro- electronic, optical and many other areas has broad application prospects.
Nature, however, very few natural diamond, high temperature and pressure through the synthesis of artificial diamond due to size restrictions and expensive, making it difficult with the excellent performance of the diamond is widely used in actual production. In 1982, Matsumto other people to use chemical vapor deposition (CVD) diamond films were prepared for the application of diamond opens up new ways to set off a worldwide wave of CVD diamond film. At present, China has also stepped up investment in diamond film research, there are a number of research units put a lot of manpower and material resources for the development and application of diamond research. According to domestic technology development status and economic development characteristics of thin film coatings of diamond tools, diamond heat sink substrate, field emission display devices, surface acoustic wave devices and the application of nano-diamond films are expected to gradually enter the market. Among them, the use of diamond in high hardness, high thermal conductivity, low coefficient of friction so on, which will be used to make diamond film coated indexable inserts a simple and complex shapes of tools, solve the non-ferrous metals and alloys, and high wear composite materials processing problems. Therefore, CVD diamond film coated tools in cutting and processing has broad application prospects.
2. Diamond film preparation methods and quality assessment of CVD
2.1 Preparation of CVD diamond films
Currently using CVD synthetic diamond film There are many ways, including: hot-filament CVD method, electron acceleration CVD method, DC discharge plasma CVD method, DC plasma jet CVD, microwave plasma CVD method, electron cyclotron resonance CVD, high frequency plasma CVD, combustion flame method, laser-induced CVD, hollow cathode plasma CVD method. CVD method in a variety of integrated indicators of good research units are widely used in microwave CVD and hot filament CVD method.
2.2 Evaluation of diamond film quality
Quality diamond films currently used detection methods are: films with Raman spectroscopy measurements, purity and membrane stress state. As a result, if compared to natural diamond 1332/cm peaks shifted to lower wave number, indicating that stress is tensile stress within the diamond; the contrary, that the membrane stress to compression stress. X-ray diffraction analysis of thin film surface structure of diamond crystal. film surface morphology by scanning electron microscopy, nucleation rate and growth rate. infrared transmittance with IR film. indentation method using membrane-based interface adhesion (membrane-based interface of diamond film adhesion is an important tool for performance evaluation). Recent studies show that diamond films measured bubble elastic modulus, Poisson's ratio, residual stress, etc., is a very promising mechanical properties of diamond films measurement method.
3.CVD diamond film coating Tool Overview
3.1CVD tools coated with diamond film substrate pretreatment
Ideal tool material should have excellent wear resistance to extend tool life; with high fracture toughness to withstand the high cutting force. But most have good fracture toughness of the tool material (such as high speed steel) usually do not have good wear resistance, and high wear resistance of materials (such as ceramic materials) are often in poor fracture toughness. As the carbide (WC-Co) materials both good wear resistance and a relatively high fracture toughness, and therefore widely used at home and abroad CVD diamond film coating tool substrate material. However, diamond films and cemented carbide big difference in the coefficient of thermal expansion, after the deposition poor interfacial adhesion, and carbide in the Co binder phase in the deposition process plays a role in promoting graphitization of diamond nucleation have inhibition. In order to improve the surface of cemented carbide tools the quality of diamond film deposition, the substrate surface must be appropriate pretreatment (used hard coating material and substrate mechanical and thermal characteristics table).
Table used hard coating material and substrate mechanical and thermal characteristics
Material – the melting point or decomposition temperature ( )-HV hardness (MPa) – Young's modulus (KN/mm2) – coefficient of thermal expansion (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 Now widely used substrate surface preparation methods: de Co surface treatment: The HCl, HNO3, H2SO4, etc. on the substrate surface layer for etching Co; with hydrogen or oxygen-hydrogen plasma plasma etching Co; the use of chemical reagents and other methods to make the substrate surface passivation layer in the Co lost activity; by chemical reaction of replacement Co, the cemented carbide tool substrate into the chemical reagents, the use of replacement reaction to the surface layer The Co substitution into other substances (such as Cu).
in the diamond film and the intermediate layer between the substrate pre-deposition, these buffer layer should meet the moderate coefficient of thermal expansion, chemical stability, and carbide and diamond have good adhesion, stability can be react with Co compound requirements. Interlayer materials widely used at present are: Ti, B, TiC, TiN, Cu, etc.; composite interlayer: WC / W, TiN / TiCN / TiN, TiCN / Ti and so on. Since the existence of intermediate layer can be eliminated between the diamond film and cemented carbide substrate lattice mismatch between thermal expansion coefficient caused by internal stress, and prevent excessive carbon in the deposition process or a Co basal infiltration depths from the substrate to surface diffusion, thus enhancing the nucleation density and adhesion. surface seeding treatment. Containing diamond powder suspension (such as acetone) on the cemented carbide substrate surface treated with ultrasound or nano-diamond powder by acetone and spread evenly over the substrate surface, and then rapidly heated with a laser, so that diamond powder embedded in the surface binding phase may enhance the nucleation density. In addition, the surface chemical cleaning, ultrasonic cleaning liquid hydrogen
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