1. Filament Power Supply 2. DC Power Supply 3. Hot Filament 4. Substrate 5. Sample Table 6. Inlet 7. Vent 8. Reaction Chamber Figure 1 EACVD Diamond Deposition Device
1 Introduction Diamond has excellent properties such as high hardness, good wear resistance, high thermal conductivity, low coefficient of friction, small thermal expansion coefficient, and strong chemical inertness. It is an ideal material for manufacturing cutting tools. In the past decade, domestic and foreign companies have developed CVD diamond thick film welding tools that can be used for non-ferrous metals, electrode graphite, ceramics, composite materials and other precision machining, and basically completed the commercial development of CVD diamond tools. The CVD diamond thick film welding tools currently used in many manufacturing processes include: preparation of large-diameter diamond thick films → laser cutting heads → brazing tool heads and tool holders in a vacuum or protective atmosphere → tool sharpening. One of the key processes is the welding of the tool head and tool holder. Due to the high interfacial energy between diamond and the low melting point metal and its alloy, it is difficult for the diamond to be wetted by the general low melting point solder alloy and the weldability is extremely poor. This problem also exists because CVD diamond is a purely crystalline polycrystalline diamond material. Although the welding strength can be improved by welding with titanium-containing silver-copper alloy solder in an inert protective atmosphere or in a vacuum, this method is not only costly, but also often the cutter head is detached during the sharpening process. Yield. Therefore, it is necessary to research and develop a simpler, more reliable, and lower cost diamond welding process. This article conducted a pilot study. 2 Test Methods This test is to adopt a new process scheme to manufacture CVD diamond thick film welding lathes. The process flow is: preparation of large-size diamond thick film → laser cutting tool head → metal surface of the cutter head (chemical vapor deposition W film) → Brazing metallized cutter heads and tool holders in the atmosphere → tool sharpening. Preparing a CVD Diamond Thick Film A self-developed electron-assisted chemical vapor deposition (EACVD) device (see Figure 1) was used to prepare a large-diameter diamond thick film 0.8 to 1.0 mm thick on a Ø100 mm Si substrate. The deposition process conditions are shown in Table 1.
Table 1 CVD diamond deposition process substrate material reaction pressure
(t) H2 traffic
(sccm) CH4 flow
(sccm) O2
flow
(sccm) substrate temperature
(°C) Filament temperature
(°C) Distance between filament and substrate
(mm) Substrate DC Current Density
(mA/cm2) Si, Mo 50 to 70 400 to 800 40 to 80 15 to 30 800 to 1000 to 2300 8 to 10 200 to 1000 Cutting of a diamond cutter head using a laser precise machine to cut a large-sized diamond thick film prepared An equilateral triangle head with a 4.0-mm edge length is used and boiled and cleaned with a mixture of H2SO4 and HNO3 to remove the residual graphite at the edge of the cut to avoid affecting the bonding between the metallized layer and the diamond. Diamond Surface Metallization The W metal layer was prepared on the surface (growth surface) of the diamond blade using chemical vapor deposition of tungsten chlorination and hydrogen reduction. In the experiment, the deposition temperatures were 800° C., 850° C., 900° C., 950° C., and 1000° C., respectively, and the deposition pressure was −80 Torr. The deposition time was 20-30 min. The welding head of the cutter head and tool holder is YG6 cemented carbide, and it is made of common Ag-Cu alloy solder. It is welded with high-frequency induction heating in the atmosphere. The welding temperature is 850°C and it is air-cooled after welding. Tool grinding Grinding welding tools using conventional diamond tool sharpening process, the tool grinding the main angle of declination 60 °, declination angle 15 °, rake angle 5 °, relief angle after 8 ° turning tools . 3 Test results and analysis Quality inspection of diamond cutter head material Figure 2 shows the Raman spectrum of the prepared CVD diamond cutter head. As can be seen from the figure, there is a sharp and high-intensity diamond characteristic peak at 1332 cm-1, indicating that the material is a pure crystalline diamond with no graphite and amorphous carbon components. FIG. 3 is a scanning electron microscope (SEM) photograph of a diamond tip. As can be seen from the figure, the diamond grains have a clear facet, dense packing, and coarse grain sizes, indicating that the diamond film has good crystal quality. From the test results, it can be seen that the prepared CVD diamond cutter head material is a pure crystalline polycrystalline diamond with good quality.
Fig. 2 Raman spectrum of diamond blade
Fig. 3 SEM image of a diamond cutter head
Effect of Diamond Surface Metallization on Brazing Effect The welding effect of diamond and carbide tool holders can be qualitatively characterized by whether or not the cutter head is detached after welding (all tool samples have the same sharpening process). The effect of the preparation process of the metallized layer on the surface of the cutter head on the brazing effect is shown in Table 2. Scanning electron microscopy analysis showed that the thickness of the W layer was 4-6 μm.
Table 2 Brazing effect of metallized
cutter heads at different temperatures Metalized layer material W Deposition temperature 800°C 850°C 900°C 950°C 1000°C Brazing conditions Atmospheric environment, high-frequency induction heating 850°C Grinding results Cutter head peeling tool Eligible failure form metallization layer W film and diamond detachment, exposing the diamond growth surface no failure Metal W is a strong carbide forming element, can interact with diamond surface carbon atoms at high temperature (900 ~ 1000 °C), generate Stable carbide WC, thus achieving a strong chemical bond with diamond; due to W's thermal expansion coefficient close to that of diamond, the thermal stress produced by high temperature deposition is lower, and the deposited W layer has a good bond strength with diamond, plus W The wettability with the Ag-Cu alloy solder is better, so by depositing a layer of metal W film on the surface of the CVD diamond, the poor wettability between the diamond and the low-melting-point alloy solder can be better solved. The diamond cutter head and the steel or carbide cutter Shelves are not easy to weld. In addition, the W metallization layer on the surface of CVD diamond can block the direct contact between diamond and oxygen when welding in the atmospheric environment, preventing the diamond from being oxidized at high temperatures. Therefore, the welding can still obtain good results in the atmospheric environment up to 850°C. Welding effect. After the surface W metallization process, the high-temperature brazing process, which can only be performed in a vacuum or protective atmosphere, can be performed in the atmospheric environment, which is advantageous in reducing the welding cost and improving the welding strength. The sharpening results show that CVD diamond deposits a layer of 4-6 μm thick metal W at a temperature of 900-1000°C to achieve good bonding with a low-melting alloy solder. The results of post-weld sharpening and cutting tests show that the new process is firmly welded and fully meets the requirements for use. It can also be seen from Table 2 that when the deposition temperature of W is lower than 900° C. during the metallization treatment, the bonding strength between the W layer and the diamond is not high, and the W film is easily detached from the diamond when subjected to impact during welding. The reason may be that the thickness of the interfacial transition layer of the carbide deposited between the W film and the diamond under the condition of less than 900 DEG C is insufficient, thereby affecting the bonding strength. The cutting performance of the diamond thick film welding turning tool was performed on a domestically-made precision lathe with a sharp-edged CVD diamond thick film welding turning tool. The cutting conditions of the Al rod were tested. The cutting conditions and the machining results are shown in Table 3.
Table 3 Cutting conditions and cutting effect of diamond turning tool Cutting material processing surface roughness Ra
(μm) Speed
(r/min) depth of cut
(mm) Cutting amount
(mm/r) Pure Al (as-cast) 1700 0.05 0.02 0.1 Pure Al (forged) 1700 0.05 0.02 0.08 As can be seen from Table 3, the surface roughness of Al parts machined with a CVD diamond thick film welding tool is extremely small. The grinding effect of ordinary grinding machines can be realized by car grinding. 4 Conclusions The chemical vapor deposition of a W metal film on the surface of CVD diamond can improve its wettability with low-melting-point alloy solders and solve the problem of poor weldability of CVD diamonds. Through the W metallization treatment on the surface of the CVD diamond cutter head, it is possible to weld the carbide tool holder under atmospheric conditions. Processing non-ferrous metals with CVD diamond thick film cutters can achieve high-quality machining surfaces for the purpose of vehicle grinding.
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