| Abstract: Analyze the advantages and disadvantages of current various tool materials, review the history of carbon nitride, and analyze the feasibility of application of carbon nitride coating on tools. By studying the practical effects of carbon nitride tools, it is considered that carbon nitride tools will have a broad Application prospects. |
The tools commonly used in machining include high-speed steel tools, carbide tools, titanium nitride tools, cubic boron nitride tools, diamond tools, and ceramic tools. These tool materials have their own advantages and disadvantages and cannot be completely replaced. For simple machining of hard surfaces (such as turning), tools such as cemented carbide and cubic boron nitride can be used, but for hard surface machining of complex workpieces (such as gears), tools such as hard alloy and cubic boron nitride are used. There is nothing you can do and you need to find other processing methods such as grinding and EDM. However, these processing methods have low processing efficiency, and EDM has the disadvantage of high cost, and some complicated workpieces cannot adopt the above method. If a method is found to enable the cutter to be cut, the work efficiency and cost can be greatly improved.
1 History and performance of carbon nitride
Carbon nitride is a new type of superhard material that emerged in the early 1990s. In the late 1980s, Cohen et al. predicted by theory that the compound b- C 3 N 4 similar to the b -Si 3 N 4 structure may have a hardness exceeding that of diamond, which immediately attracted widespread attention from researchers at home and abroad. In 1993, Niu first announced the use of laser ablation to obtain a b- C 3 N 4 film. Subsequently, the researchers successfully synthesized carbon nitride films by electron cyclotron resonance-chemical vapor deposition (ECR-CVD), hot filament CVD, reactive magnetron sputtering. The hardness of the synthesized carbon nitride film is also increasing. Japan's Fujimoto et al. used a particle beam hybrid deposition method to form a CN x film hardness of 63 GPa on a carbide substrate.
Wuhan University has been studying the synthesis of carbon nitride since 1994. The carbon nitride film was successfully synthesized by RF CVD, magnetron sputtering, etc., and the coating process of carbon nitride film on high speed steel substrate was studied. According to available data, the deposition of carbon nitride film on tools is the first in the world.
| material | High speed steel | Cemented carbide | TiN | Cubic boron nitride | Diamond | Carbon nitride |
| HRC | 6266 | 7481 | - | - | - | - |
| HV (GPa) | 89 | 1318 | twenty one | 47 | 800 | 50 |
The superhard nature of carbon nitride is the key to its application on tools. As can be seen from Table 1, the plating of carbon nitride on the surface of the tool greatly increases the surface hardness of the tool.
Carbon nitride also has good thermal stability. Thermal stability (TG)-differential thermal analysis (DTA) was used to study the thermal stability of carbon nitride from room temperature to 1200 °C. It was found that samples with a small graphite phase content showed no significant thermal weight loss in the above range, which proved that the carbon nitride film Has good thermal stability, see Figure 1.
 Figure 1 Carbon Dioxide Film Weight Loss (TG)-Differential Thermal Analysis (DTA) |
The corrosion resistance of carbon nitride film was found to reduce the anodic corrosion current density of the carbon nitride coated steel sample to 0.4% of bare metal and 1.3% of chrome-plated steel sample during electrochemical corrosion. It can be seen that the carbon nitride coating can reduce the corrosion rate and has good corrosion resistance. At the same time, the covalent bond of CN in carbon nitride is different from the covalent bond of CC in diamond. N is more electronegative and binds carbon atoms, making it difficult to react with Fe, making it useful. For cutting black metal.
2 The effect of carbon nitride tools on the processing of hard materials
We conducted a pre-machine test of a pinion knife coated with a carbon nitride film. The test results are shown in Table 2. Due to the deformation of the gear through the quenching carburizing heat treatment, the tolerance of the common normal line does not meet the design requirements, but the surface hardness of the gear after quenching and carburizing reaches HRC62 or above, and the gear design shape is special and cannot be ground, so that the gear waste The rate reached 80% or more. The carbon nanotube plucking knife can be used to finish the heat-treated gear to meet the design requirements, greatly improving the yield.
| Pinion cutter | Diameter (mm) | 117 | |
| Material | W18Cr4A | ||
| Modulus | 9 | ||
| Cut gear | Diameter (mm) | 180 | |
| Material | 20Cr2Ni4A | ||
| Hardness (HRC) | > 60 (carburized and quenched) | ||
| Cutting parameter | Number of strokes (times / mm) | 83 | |
| Cutting speed (m/min) | 10 | ||
| Feed rate (mm/tooth) | 0.1 | ||
| Cutting result | White knife | Number of cutters | 0 |
| abrasion | Serious wear and tear on the tool | ||
| Yellow knife | Number of cutters | 4 | |
| Surface roughness Ra (μm) | 3.2 | ||
| Wear (mm) | 0 . 2 | ||
| Test machine | Y54A | ||
| Test manufacturer | The People's Liberation Army No. 3303 Factory | ||
| Note: White knife—the uncoated CN x / / TiN composite film cutter; | |||
 Figure 2 Gears and pinion cutters before and after machining |
In the middle of Fig. 2 is the plated cutter, the upper left is the gear before finishing, and the right is the processed gear. The processed tooth surface is smooth and smooth.
During the test, we noticed that because the material to be processed is very hard, the tool will not wear before the carbon nitride coating on the tool wears. Once the coating is worn, the tool is immediately worn and can no longer be processed. The carbon nitride coating provides good protection for the tool.
In addition, preliminary tests on carbon nitride film on indexable carbide turning tools have shown that turning tools with carbon nitride film can be used for turning hardened steel with hardness of HRC62.
3 Prospects for carbon nitride tools
High-speed steel is a widely used tool material, especially for tools with complex shapes, such as drills, taps, milling cutters, etc., as well as some forming tools with strict dimensional accuracy, such as gear shaping cutters and hobbing cutters. The use of cemented carbide materials for these tools is economically uneconomical, and carbide grinding is difficult and it is difficult to manufacture certain tools. For example, in commonly used gear cutters, cemented carbide can only produce tools with a modulus of less than 3, and is extremely expensive. If a carbon nitride coated gear cutter made of high speed steel is used, it can not only reduce the cost of the tool but also the hard surface that can not be cut by the hard alloy. According to the available data, the better forming tools can only process the material of HRC52, and the carbon nitride tool can process various materials of HRC62.
High-speed steel as a tool material generally has a hardness of more than HRC60. The main reason for the damage of high-speed steel tools in use is that the cutting edge of the tool causes the machining accuracy to be less than required. In general, the case where the base is recessed does not occur during machining. The main reason for the chip's embrittlement is that the adhesion of the film is low. As long as the film growth process meets the requirements and the adhesion of the film is improved, the film is less likely to be brittle.
Due to the high hardness of the carbon nitride tool and the flexibility in tool manufacturing, it can replace partial grinding and improve work efficiency. It can also replace some other tools (such as boron nitride tools) and some other processing methods (such as EDM), saving tool costs and saving energy. In the machining of many large workpieces, the tool wear often requires the machining to be replaced, so that the machining accuracy cannot be guaranteed. The high hardness and good wear resistance of the carbon nitride tool are suitable for this kind of occasion, and can be processed at one time to ensure the processing precision and improve the production efficiency.
Tests have shown that carbon nanotube-coated drills have a 25-fold increase in life over uncoated drills and a three-fold increase in life compared to titanium nitride-coated drills. It can be seen that the carbon nitride cutter has a longer life and can reduce the cost of the cutter.
In order to achieve a higher hardness of the film and avoid the precipitation of the soft phase, it is difficult to adopt a special process in the film growth process. At present, the laboratory has made the process reach the level of industrial production, and the tool coated with carbon nitride coating will soon be mass-produced. Because it can replace many of the original inefficient processing methods and greatly improve work efficiency, it has broad market prospects and high economic value.
In summary, the carbon nitride coating not only improves the tool life, but also performs hard surface processing, which can be easily achieved by many unworkable workpieces or other time-consuming and labor-intensive processing methods. The emergence of carbon nitride tools brings new life to machining, and it will have broad application prospects.
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