JP3397849B2 - Diamond coated cemented carbide tool - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diamond-coated cemented carbide in which a cemented carbide is used as a tool base material, and the surface of the base material is coated with a diamond thin film by a vapor phase synthesis method. More particularly, the present invention relates to a diamond-coated cemented carbide tool which achieves excellent adhesion between a base material and a diamond thin film and is suitable for cutting nonferrous metals and ceramic materials. 2. Description of the Related Art Diamond has a very high hardness as compared with alumina, silicon nitride, cemented carbide and the like which have been widely used as a conventional hard material, and has a high thermal conductivity. And is used as a material for wear-resistant tools. In particular, a diamond sintered body tool using a diamond sintered body synthesized by sintering diamond powder under ultra-high pressure and high temperature is widely used as a cutting tool and a polishing tool for non-ferrous metals and ceramic materials. However, diamond sintered bodies are expensive and have no higher hardness than diamond, so that there is a problem that they are difficult to apply to drills, end mills, and the like having complicated shapes and small diameters. Recently, it has become possible to form a diamond thin film on a base material by a chemical vapor synthesis method using a carbon-containing gas excited by a microwave or a hot filament as a source gas. However, since this technique can easily and inexpensively form a diamond thin film even for a tool having a complicated shape, research and development of a diamond-coated tool are being actively promoted by applying this technique. However, a diamond thin film synthesized in a gas phase has a very small coefficient of thermal expansion and can be synthesized only at a high temperature of about 600 to 1100 ° C. There is a problem that good adhesion to the base material cannot be achieved due to thermal stress generated by a difference in thermal expansion coefficient from the base material during cooling. From the viewpoint of avoiding such inconveniences, attempts have been made to use a material such as silicon nitride or sialon whose coefficient of thermal expansion is not so different from that of a diamond thin film as a base material, thereby making it possible to considerably improve adhesion. I have. However, materials such as silicon nitride and sialon have low toughness, and when such a material is used as a base material as a cutting tool, there is a disadvantage that the cutting edge is easily chipped. On the other hand, cemented carbide is superior in terms of toughness, and it is desired to use cemented carbide as a tool base material, but the thermal expansion coefficient is higher than diamond,
When the diamond thin film is synthesized at the above-described base material temperature, a residual stress of about 1 GPa is generated in the diamond thin film, and in some cases, the diamond thin film is separated from the base material during cooling of the base material. The present invention has been made in order to solve the technical problems as described above, and its purpose is to achieve excellent adhesion between a cemented carbide base material and a diamond thin film, making it ideal for various tools. An object of the present invention is to provide a diamond-coated cemented carbide tool having mechanical properties. SUMMARY OF THE INVENTION The present invention, which has achieved the above object, relates to a diamond-coated cemented carbide tool in which a diamond thin film is coated on the surface of a cemented carbide tool base material by a vapor phase synthesis method. The thickness of the diamond thin film is 1-2
0 μm, and the diamond thin film has a thickness of 0.0
The diamond-coated cemented carbide tool has a gist in that 001 to 1 atomic% of nitrogen is doped and a tensile stress is applied to the diamond thin film. As described above, one of the causes that the diamond thin film of the diamond coated cemented carbide tool is easily peeled off is that the coefficient of thermal expansion of the diamond thin film is smaller than that of the cemented carbide base material. It is due to. That is, the thermal expansion coefficient of the diamond thin film is about 3.1 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the cemented carbide is about 4 to 6 × 10 ⁻⁶ / ° C. If the temperature is 1000 ° C., about 1 to 2 GPa of compressive stress is theoretically applied to the diamond film. However, this compressive stress is a value assuming that no film stress is generated when a diamond thin film is synthesized. In practice, a tensile stress is generated in a diamond thin film at the time of film formation, and a compressive stress is generated. (Residual compressive stress) is lower than the above value. However, the tensile stress is at most about 0.5 GPa, and does not completely reduce the compressive stress caused by the difference in thermal expansion coefficient. The present inventors have made various studies from the viewpoint of alleviating the compressive stress of the diamond thin film. As a result, when the diamond thin film is subjected to vapor phase synthesis, if nitrogen is doped into the diamond thin film, the tensile stress generated during the formation of diamond can be increased to be substantially equal to the compressive stress, The inventors have found that the residual stress can be reduced, and completed the present invention. FIG. 1 shows the relationship between the nitrogen concentration in the reaction gas and the residual tensile stress when the diamond film is doped with nitrogen by changing the nitrogen (N ₂ ) concentration in the reaction gas in the range of 0 to 1% by volume. It is a graph which shows the result of having investigated the relationship. The diamond film synthesis conditions at this time are as follows.
The diamond film was placed on a Si substrate (5 mm × 20 mm × 0.4) so that the tensile stress could be easily measured as the residual tensile stress.
7 mm), and the residual tensile stress was determined by measuring the amount of warpage of the Si substrate. In addition, morphology, film quality, and the like were examined by a scanning electron microscope, Raman analysis, and X-ray diffraction. (Synthesis conditions) Reaction gas: mixed gas of H ₂ (flow rate: 100 SCCM) and ethanol (flow rate: 3 SCCM) Filament temperature: 2
200 ° C. Si substrate temperature: 1000 ° C. Pressure: 80 Torr Synthesis time: 2.5 hours As is apparent from FIG. 1, the residual stress is a tensile stress over the entire nitrogen concentration. It can be seen that the stress increases up to approximately 0.5% by volume. Up to a nitrogen concentration of 0.5% by volume, the surface morphology of the diamond thin film hardly changed. On the other hand, as the nitrogen concentration increased beyond 0.5% by volume, the stress decreased, but the surface morphology changed accordingly. That is, when the nitrogen concentration exceeded 0.5% by volume, the crystals of the (100) plane were oriented, and when the concentration further increased, microcrystallization was observed. Thus, the effect of nitrogen doping on the residual stress was correlated with the crystal morphology, and the decrease in the residual stress was considered to be due to the segregation of non-diamond carbon at the grain boundaries. In any case, if a predetermined amount of nitrogen is contained in the reaction gas to synthesize a diamond thin film and dope the diamond thin film with nitrogen, the tensile stress in the diamond thin film could be increased. The above effect is obtained by doping with nitrogen because the nitrogen atom is substituted at the position of the C atom in the diamond lattice. As such an element, besides nitrogen, there is also boron (B).
It is thought that the same effect can be exerted by doping in diamond. However, the present inventors have confirmed through experiments that it has been found that B does not have the same effect as nitrogen. The present inventors included B (0.5% by volume) instead of nitrogen in the above-described reaction gas, changed the filament temperature: 2150 ° C., the Si substrate temperature: 950 ° C., and synthesized time. Except for changing the diamond (film thickness), a diamond thin film was synthesized under the same synthesis conditions as described above, B was doped into the thin film, and the effect on the residual tensile stress was investigated. The result is shown in FIG. For comparison, FIG. 2 also shows the results obtained when the nitrogen concentration in the reaction gas was 0.5% by volume and 0% (no doping was performed). As is clear from these results, the B-doped one has a smaller residual tensile stress than the B-doped one,
It has been found that the doping of B acts on the compressive stress side rather. The results of FIG. 1 show the nitrogen concentration in the reaction gas as a parameter, and the amount of nitrogen actually doped in diamond is not determined only by the nitrogen concentration in the reaction gas. However, it varies depending on, for example, the composition of the reaction gas and the synthesis conditions. For this reason, in the present invention, the amount of nitrogen to be doped in the diamond thin film is specified, and the amount of nitrogen needs to be 0.0001 to 1 atomic%, for the following reason. That is, when the nitrogen concentration in the diamond thin film is out of the above range, the tensile stress in the diamond thin film becomes smaller than about 1 GPa, and the compressive stress due to the difference in the thermal expansion coefficient cannot be completely reduced. Therefore, it is necessary to appropriately set the reaction gas composition and the synthesis conditions so that the nitrogen concentration in the diamond thin film falls within the above range. On the other hand, since the tensile stress of the diamond thin film coated on the surface of the cemented carbide base material is affected by the thickness of the diamond thin film and the base material temperature at the time of synthesis, it is necessary to set these appropriately. From such a viewpoint, the thickness of the diamond thin film needs to be 1 to 20 μm. If the thickness is out of the above range, the tensile stress of the diamond thin film is extremely reduced, and the compressive stress cannot be reduced. on the other hand,
As described above, the temperature of the substrate during the synthesis is required to be at least about 600 to 1100 ° C. in order to perform the gas phase synthesis, but it is better to be as low as possible in consideration of reducing the compressive stress. The higher the better, the better. In the present invention, as shown in Examples below, it is appropriate that the base material temperature is about 750 to 1000 ° C. The means for synthesizing the vapor-phase synthetic diamond is not particularly limited. For example, a chemical vapor deposition method (excitation decomposition of a raw material gas of hydrogen and hydrocarbon with a thermionic emitting material or a microwave non-polar discharge, etc.) CVD method). The means for doping nitrogen in the diamond thin film is not particularly limited. For example, in addition to mixing nitrogen gas into the raw material gas, nitrogen gas such as acetaldehyde oxime, methylaminoethanol, dimethylacetamide, ethylaminoethanol, etc. The organic compound to be used may be mixed with hydrogen and used as a source gas. Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and any design changes mentioned in the preceding and following paragraphs are intended to It is included in the technical scope. EXAMPLE 1 H ₂ : 200 cc / min, acetaldehyde oxime (CH ₃ CH = NOH): ₂ cc / min as a raw material gas
Using a mixed gas of the following conditions, under the conditions of a pressure of 40 Torr and a microwave output of 1 kW by a microwave plasma CVD method,
A diamond having a thickness of 2 μm was synthesized on the cemented carbide chip in 30 minutes to produce a diamond-coated cemented carbide tip of the present invention. The obtained chip was examined for nitrogen concentration in the diamond film by a secondary ion mass spectrometer.
Atomic% nitrogen was included. On the other hand, H ₂ : 200 cc /
min, CH ₄ : Using a mixed gas of 2 cc / min, by microwave plasma CVD, at a pressure of 40 Torr.
r, microwave output: 1 kw, a 2 μm-thick diamond thin film was synthesized on a cemented carbide tip having the same shape as above, and a diamond-coated cemented carbide tip as a comparative material was also manufactured. For these chips, the work material Al-1 was used.
Cutting speed: 400 m / m using a 2% Si alloy round bar
Dry cutting was performed under the conditions of in, depth of cut: 0.1 mm, feed: 0.1 mm / rev, and the cutting performance was evaluated. As a result, the chip of the comparative material was peeled off in 5 minutes after cutting, but the chip of the present invention did not peel off in 90 minutes after cutting. Example 2 By a hot filament CVD method using a tantalum filament having a diameter of 0.5 mm, a mixed gas obtained by adding a nitrogen gas to a gas consisting of hydrogen-ethanol vapor was used as a raw material gas under the conditions shown in Table 1 below. A diamond thin film was formed on a cemented carbide tip. These chips were subjected to a 90-minute cutting test in the same manner as in Example 1. The results are shown in Table 2. From the results, it can be seen that the diamond-coated superhard tip of the present invention shows excellent adhesion without peeling. [Table 1] [Table 2] Example 3 As source gas, H ₂ : 200 cc / min, CH ₄ : 2c
c / min, NH ₃ : Using a mixed gas of 0.1 cc / min, by microwave plasma CVD, at a pressure of 40
Torr, microwave power: 1 kw, diameter: 5
A 3 μm-thick diamond thin film was synthesized on a 30 mm carbide end mill in 30 minutes to produce a diamond-coated carbide end mill of the present invention. About the obtained end mill, 2
When the nitrogen concentration in the diamond film was examined using a secondary ion mass spectrometer, it was found that 0.1 atomic% of nitrogen was contained. On the other hand, as a comparative material,
₂ Using a mixed gas of 200 cc / min, CH ₄ : ₂ cc / min, by a microwave plasma CVD method under the conditions of a pressure of 40 Torr and a microwave output of 1 kW, a 3 μm-thick film was formed on a carbide end mill having the same shape as above. A diamond-coated carbide end mill as a comparative material was prepared by synthesizing diamond. Using these end mills, Al-16%
Side cutting of the Si alloy was performed. The cutting conditions at this time are:
Cutting speed with down cut: 80m / min, feed rate:
0.03 mm / min, depth of cut: 5 mm, cutting width: 2
mm. As a result, the end mill of the comparative material peeled off in 20 minutes of cutting, but the end mill of the present invention did not peel off even after cutting for 120 minutes, and a good work surface was obtained. As described above, according to the present invention, by doping nitrogen into diamond, a compressive stress caused by a difference in thermal expansion coefficient between diamond and a base material is reduced by a tensile stress generated during film formation. Thus, a diamond-coated cemented carbide tool having excellent adhesion was obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a relationship between a nitrogen concentration in a reaction gas and a residual tensile stress of a diamond thin film. FIG. 2 is a graph showing a comparison between the doping effects of nitrogen and boron.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiki Sato 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Steel, Ltd. Kobe Research Institute (72) Inventor Tatsuya Yasunaga Nishi-ku, Hyogo-ken 1-5-5 Takatsukadai Kobe Steel Engineering Co., Ltd.Kobe Research Institute (72) Inventor Kazuhisa Kawada 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture Kobe Steel Co., Ltd.Kobe Research Institute (72) Inventor Masanori Tsai 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Kobe Steel, Ltd. Kobe Research Institute (56) References JP-A-64-75678 (JP, A) JP-A Sho 63-53269 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 16/26-16/27 C30B 29/04 B23B 27/14 B23P 15/28

Claims (1)

(1) In a diamond-coated cemented carbide tool in which a diamond thin film is coated on the surface of a cemented carbide tool base material by a gas phase synthesis method, the diamond thin film has a thickness of 1 to 5. 20 μm, and
One, this is the diamond thin film is 0.0001 atomic percent of nitrogen is doped, diamond-coated cemented carbide tool, characterized in that in which the tensile stress on the diamond thin film is applied.