Survey of CVD diamond film coating tools
1 Introduction Next page
Diamond has excellent physical and chemical properties, has the highest hardness among all materials in nature, has the highest thermal conductivity at room temperature, and has a very low coefficient of thermal expansion, low friction coefficient, good chemical stability, and large forbidden band. Width (5.5eV), highest acoustic propagation speed, high semiconductor doping and optical transmission from the far infrared region to the ultraviolet region, so many excellent properties make it in machining, microelectronics, optics Many fields have broad application prospects. However, the amount of natural diamond in nature is extremely small, and synthetic diamonds synthesized by high temperature and high pressure are limited in size and expensive, so that diamonds having excellent properties are difficult to be widely used in actual production. In 1982, Matsumto et al. used chemical vapor deposition (CVD) to prepare diamond films, which opened up new avenues for the application of diamonds, which led to a worldwide CVD diamond film research boom. At present, China has also increased investment in research on diamond films. A number of research units have invested a large amount of manpower and material resources in the development and application of diamond films. According to the status quo of domestic technology development and economic development, the application of diamond film coating tools, diamond heat sink substrates, field emission display devices, surface acoustic wave devices and nano-diamond films are expected to enter the market. Among them, diamond film coating is used to make simple indexable inserts and complex shape cutters by using diamonds with high hardness, high thermal conductivity, low friction coefficient, etc., which can solve non-ferrous metals and their alloys and high wear resistance. Processing problems such as composite materials. Therefore, CVD diamond film coating tools have broad application prospects in the field of cutting.
2. Diamond film CVD preparation method and quality evaluation
2.1 Diamond film CVD preparation methods Currently, there are many methods for synthesizing diamond films by CVD, including: hot wire CVD, electron accelerated CVD, DC discharge plasma CVD, DC plasma jet CVD, microwave plasma CVD. Method, electron cyclotron resonance CVD method, high frequency plasma CVD method, flame method, laser induced CVD method, hollow cathode plasma CVD method, and the like. Among the various CVD methods, the comprehensive index is preferably the microwave CVD method and the hot wire CVD method widely used by the research unit.
2.2 Diamond film quality evaluation methods Currently used diamond film quality testing methods are: 1 Raman spectroscopy is used to measure film structure, purity and intramembrane stress. The result is that the internal stress of the diamond is tensile stress relative to the characteristic peak of the natural diamond of 1332/cm, indicating that the internal stress of the diamond is tensile stress; otherwise, the internal stress of the film is compressive stress. 2 The crystal plane structure of the thin film layer diamond was analyzed by X-ray diffraction. 3 The surface morphology, nucleation rate and growth rate of the film were observed by scanning electron microscopy. 4 Infrared spectroscopy was used to analyze the infrared transmittance of the film. 5 Determination of film-based interfacial adhesion by indentation method (film-based interfacial adhesion is an important evaluation index of diamond film tool performance). Recent research results show that the elastic modulus and Poisson's ratio of diamond film are measured by bubbling method. Residual stress, etc., is a very promising method for measuring the mechanical properties of diamond films.
3. Survey of CVD diamond film coating tools
3.1 CVD diamond film coating tool substrate pretreatment technology The 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. Due to 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 cemented carbide tools, the surface of the substrate must be properly pretreated (see Table 1 for the mechanical and thermal properties of commonly used hard coating materials and substrates).
Table 1. Mechanical and thermal properties of commonly used hard coating materials and substrates
Material - 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