Engineering application of CVD diamond film
Key words CVD, diamond film|2020-09-24 11:20:48|Source Superhard materials and abrasives
Abstract Diamond has many excellent physical and mechanical properties, such as ultra-high hardness, strength, wear resistance, and corrosion resistance. The so-called engineering application is a measure to fully develop these mechanical properties and apply them in various fields of industry. CVD diamond film is almost similar to single crystal diamond...
Diamond has many excellent physical and mechanical properties, such as ultra-high hardness, strength, wear resistance, and corrosion resistance. The so-called engineering application is a measure to fully develop these mechanical properties and apply them in various fields of industry. CVD diamond film has almost similar physical and chemical properties to single crystal diamond, and the production process is relatively simple. The application of CVD diamond coating technology to deposit the diamond film on the surface of the component substrate to make it have diamond-like properties is a very promising Engineering application projects.
1. Integral tool
With the development of modern machining in the direction of high precision, high speed and high efficiency, quite high requirements are put forward on the performance of the tool. Therefore, it is an inevitable development trend to develop superhard material tools with higher wear resistance and stable machining for a long time.
On the one hand, natural diamond resources are extremely limited and expensive; on the other hand, single crystal diamond has a cleavage surface and low impact toughness, which limits its large-scale promotion and use in industry. Although the polycrystalline diamond (PCD) tool material sintered by the high temperature and high pressure method is isotropic to solve the problem of low impact toughness of single crystal diamond, it contains about 5% of the binder component, resulting in the tool life and surface The processing quality is far lower than natural diamond tools.
The preparation technology of depositing CVD diamond film with high adhesion strength and good surface smoothness on the surface of complex shape cemented carbide substrate has always been one of the technical problems that restrict the large-scale industrial application of CVD diamond film coating tools, which greatly limits CVD The application range of diamond film.
Depositing a layer of CVD diamond film on the surface of the cemented carbide milling cutter can effectively enhance its wear resistance. In the experiments of processing graphite and processing Al/SiC-MMCs workpieces, both revealed the superiority of diamond film as a wear-resistant material on the surface of cemented carbide tools, laying a foundation for the further industrial application of diamond film.
2. Key components of coal liquefaction pressure reducing valve
The pressure reducing valve used to discharge the residue downstream of the high temperature and high pressure separator of the direct coal liquefaction process system needs to face high temperature (455℃), high pressure difference (about 20MPa), high fluid velocity (about 107m/s) and high solid state in actual work. Concentration (solid particle concentration is as high as 50% or more) extreme working conditions of fluid erosion. Therefore, very high requirements are put forward on the erosion resistance and service stability of the eroded surfaces of key components such as valve seats and valve cores.
In the past, these key components were mainly imported, but even the expensive imported components had an average service life of less than 400h. In the industrial production process of coal liquefaction, frequent equipment performance testing and component replacement are required, which seriously affects production efficiency and economic benefits. Therefore, it is of great significance to research and develop coal liquefaction pressure reducing valve seat and valve core components with independent intellectual property rights with good erosion resistance. Among the commonly used CVD diamond coating deposition methods, the hot filament CVD method has the advantages of simple deposition equipment and large area and complex shape deposition. It is very suitable for diamond coating on the arc surface of the valve seat inner hole and the outer surface of the valve core cylinder. Of deposition. The test shows that the service life of the diamond-coated pressure reducing valve components obtained by deposition reaches 1200h, which is more than 3 times longer than the service life of the traditional uncoated pressure reducing valve.
3. Milling CFRP
Carbon fiber reinforced resin matrix composites (CFRP) have excellent properties such as light weight, high strength, fatigue resistance, corrosion resistance and strong designability, and are widely used in aerospace, aviation, automotive and energy fields. Generally, the formability of CFRP parts mainly adopts near-net forming technology, but after forming, it cannot meet the requirements of precision or assembly, and often needs to be milled. CFRP is a typical difficult-to-machine material. During the processing, the carbon fiber reinforced phase with high hardness and low thermal conductivity will severely wear the tool, and the local high temperature in the cutting zone will accelerate the wear of the tool edge; the material is prone to burrs and tears after milling , Delamination and other processing defects. Traditional cemented carbide milling cutters can no longer meet their machining requirements, and wear-resistant coatings are needed. Diamond film has become an ideal material for manufacturing CFRP tool wear-resistant coatings due to its advantages of high hardness, high thermal conductivity and low friction coefficient.
The preparation process of CVD diamond-coated cutting tools is not limited by the shape of the cutting tools. After coating, the cutting tools can be used directly, which is suitable for the preparation of cutting tools with complex shapes, such as milling cutters and drill bits.
On the basis of studying the cutting characteristics of CFRP, Yang Xiaochen et al. prepared CVD diamond films with three different coating processes of coarse-grained, fine-grained, and composite crystals on the same carbide end mill substrate. Under the same cutting conditions, the carbon fiber composite material was milled and tested. The diamond-coated milling cutter of the composite crystal process has the longest service life, which is about 1.35 times that of the coarse-grain diamond-coated milling cutter. 1.59 times, more suitable for milling processing of carbon fiber composite materials.
4. Strengthen the impregnated diamond bit
Impregnated diamond bits have been used in geological exploration for decades. With the development of the application field of drilling technology in the 21st century, the continuous emergence of new requirements for geological exploration, the advancement of related technologies, the continuous transformation of drilling technology and equipment and technology, the drill bit as a rock crushing tool is also constantly innovating. Facing the situation and tasks of geological exploration at home and abroad, all countries pay more attention to the research and development of high-performance diamond drill bits. For example, DeBeers company developed an impregnated diamond drill bit strengthened by thermally stable polycrystalline diamond Syndax-3 in the 80s of the last century, and some foreigners used the composite of Balas triangular polycrystalline and artificial single crystal impregnated layer. The drill bit has a wide range of drilling medium-hard to hard formations.
The performance of the impregnated diamond bit has a great impact on the drilling efficiency and cost of geological exploration. In order to improve the performance of the bit, researchers have designed and manufactured a new type of impregnated diamond bit that uses CVD diamond strips as the hard fulcrum material. And carried out the impact rotary drilling test. The results show that: compared with the soft fulcrum impregnated diamond bit, the hard fulcrum is superior to the soft fulcrum percussion rotary drilling in terms of aging and impact resistance during rotary percussion drilling. It is a high-quality and efficient drilling technology. Especially in the hard rock drilling process, the drilling efficiency can be effectively improved, the drill bit can be reduced, and the hard fulcrum drill bit has a higher life and the drilling process is more stable.
5. Processing Zirconia Ceramics
Zirconia ceramics have excellent physical and chemical properties and are widely used in aerospace, aviation, national defense, energy and other fields. For example, in the field of oral restoration, all-ceramic teeth made from it have become a popular product in the market. It can be well adapted to the tooth work and environment, and its appearance also meets the needs of consumers. However, due to its high hardness, it is difficult to mill, and the complexity and precision required for production are also high. Therefore, the development of a tool can complete the processing of zirconia ceramics under the requirements of high efficiency, high quality and economy. Very meaningful research topic.
Wang Haiwang and others used the bias-enhanced hot-wire chemical vapor deposition method to deposit three different diamond film coatings on the cemented carbide sheet and the cemented carbide ball-end milling cutter, which are micro-diamond film (MCD) and nano-diamond film (NCD). ) And Micron Nano Composite Diamond Film (MNCD).
Through friction experiments, it is found that the friction coefficient curves of three kinds of CVD diamond film coatings and zirconia ceramic balls are relatively similar. At the beginning of the friction process, the friction coefficient is relatively large, and then in the process of friction, the friction coefficient gradually decreases, until the friction coefficient becomes relatively stable. The cemented carbide is different from the first three in that the friction coefficient is relatively small at the beginning of the friction process, and then as the friction process progresses, the friction coefficient gradually increases, but the friction coefficient will become relatively stable in the end.
Through cutting experiments, it is found that the wear of diamond-coated tools is much smaller than that of uncoated tools. Comparing three different diamond film coatings, diamond particles that have not been polished can still be observed on the surface of the MCD film. The wear morphology of the NCD and MNCD films are very similar, and the wear amount is not much different, which is smaller than the MCD film. .
6. CVD thick film cutter
Chemically deposited diamond thick film ≥0.5mm full crystal pure diamond polycrystalline structure, without any metal bond components, theoretically has both the characteristics of natural diamond and polycrystalline diamond (PCD), its performance is close to natural diamond, excellent Compared with PCD, the cost is much lower than PCD. Therefore, it will be a new type of superhard material with great development prospects.
Although the CVD diamond thick film welding tool can be brazed to the required cemented carbide substrate through a special and simple technology, the welding strength is far lower than the combination between the high-pressure sintered PCD layer and the cemented carbide. strength. When it is used for high-demand machining such as interrupted cutting, the connection of its interface becomes very fragile. If the brazing strength of CVD diamond thick film can be solved, then CVD thick film welding tools will be able to compete with PCD tools in the entire machining field.
In order to evaluate the excellent cutting performance of CVD diamond thick film welding tools, Sumitomo of Japan conducted cutting tests on various Al-Si alloys, which proved that the cutting performance and life of CVD diamond thick film welding tools are better than PCD tools. Norton said that their DiamaPak CVD diamond composite blades far exceed PCD in the processing of many non-ferrous materials, the tool life is 10 times longer than PCD, and the surface roughness is lower.
Deng Fuming and others conducted ultra-precision cutting performance research on CVD diamond thick film precision turning tools. The processed material is duralumin alloy LY12, the cutting depth is 5-6 microns, the feed rate is 0.01mm/r, and the cutting speed is 120m/min. The experimental results show that : The roughness of the machined surface is 0.05 microns, which proves that CVD diamond thick film tools can replace natural single crystal diamond turning tools for ultra-precision machining.
7. Drawing mold
The metal wire industry is my country's main traditional industry, and drawing dies are important consumables for metal wire manufacturers. The performance of the drawing die determines the quality, production efficiency and production cost of the metal wire. At present, the molds used in the wire industry are mainly two categories: cemented carbide molds and polycrystalline diamond molds. Cemented carbide molds have a short life, easy to stick materials, and low production efficiency; polycrystalline diamond molds are expensive, making it very difficult to make larger-sized molds and special-shaped molds, and has poor toughness. The use of CVD diamond coating technology to make diamond-coated drawing dies overcomes the shortcomings of hard alloy drawing dies that are not wear-resistant and polycrystalline diamond drawing dies have poor toughness and become a new generation of drawing dies.
According to observations, in actual use of the diamond-coated drawing die, the failure of the diamond-coated drawing die is not due to excessive dimensional changes due to wear, but the rough surface exposed after the diamond coating is partially peeled off, causing the wire surface to scratch and cause failure , It is essentially different from the failure of ordinary cemented carbide molds and polycrystalline diamond molds.
◆ finishing from "engineering CVD diamond films", author: WANG Guang-zu
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