JP2568542B2 - Low pressure synthesis of diamond - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a diamond film on a surface of a tungsten carbide-based cemented carbide (hereinafter referred to as a cemented carbide) substrate at a high growth rate. .

[Conventional technology]

2. Description of the Related Art Conventionally, in general, various tools and wear-resistant members in which a diamond film is formed on the surface of a cemented carbide substrate by a vapor phase synthesis method for the purpose of improving wear resistance have been widely used.

Numerous methods have been proposed for the vapor phase synthesis of diamond films. Among them, a method described in Japanese Patent Application Laid-Open No. This conventional method is characterized in that plasma is generated in a reactor by high-frequency discharge.

[Problems to be solved by the invention]

However, in the above-described conventional method, the plasma generated by the high-frequency discharge has a reaction zone of 10 times less than the case without the plasma, that is, the case with only the thermionic emission material.
Although it was more than doubled and the diamond film had improved coverage and adhesion strength, (1) the diamond growth rate was extremely slow, 0.5 to 0.6 μm / hr.

(2) The generation density of diamond nuclei is low.

At present, it takes a long time to form a diamond film having a desired thickness.

[Means for solving the problem]

Thus, the present inventors have conducted research to solve the problems of the above-mentioned conventional method, and as a result, a mixed gas of hydrocarbon and hydrogen was introduced into a reactor in which plasma was generated by high-frequency discharge. Introduced under the condition that the gas pressure is 150 to 300 torr, as a reaction gas activated by the plasma and the thermoelectron emitting material heated to a temperature of 2200 to 2500 ° C., a superheated to a temperature of 300 to 1100 ° C. When supplied to the surface of a hard alloy substrate, the density of diamond nuclei is increased and the growth rate of diamond is increased, thereby obtaining a research result that a high-speed formation of a diamond film is possible.

That is, as for the generation density of diamond nuclei and the growth rate of diamond, how much of the above-mentioned mixed gas molecule becomes an active species effective for generation of diamond nuclei and growth of diamond, and how much it reaches the substrate It is thought that it depends on whether it can last until
Based on the idea that the application of plasma has the effect of maintaining the active species generated by thermionic emission material, as described above, the pressure in the furnace of the mixed gas is set high, and the thermionic emission material is heated to a high temperature. Therefore, it is very important to increase the rate of diamond film formation by increasing the generation density of diamond nuclei and the number of excited active species that contribute to the growth of diamond, and extending the residence time in the system by the energy of plasma. The research result was obtained.

The present invention has been made based on the results of these researches, and when forming a diamond film on the surface of a cemented carbide substrate by a vapor phase synthesis method using a thermionic emitting material, a mixed gas of hydrocarbon and hydrogen is used. Into the reactor where plasma was generated by high frequency discharge,
~ 300 Torr, and the plasma and 220
A diamond film is formed at a high growth rate by supplying a reactive gas activated by the thermionic emission material heated to a temperature of 0 to 2500 ° C. to the substrate surface heated to a temperature of 300 to 1100 ° C. The method has features.

In the method of the present invention, hydrocarbons include paraffinic hydrocarbons such as methane, ethane, propane and butane, olefins, acetylenes, diolefins,
In addition to aromatic hydrocarbons such as all hydrocarbons, ethers, alcohols, which also includes organic halogen-based, the ratio of H ₂ to hydrocarbon 10-10000 C.,
This means that if it is smaller than 10, graphite will be generated and 10,000
This is because it is difficult to form diamond when the temperature exceeds the limit, and a filament of W, Ta, Mo, LaB ₆ or the like is preferable as the thermionic emission material.

Further, in the method of the present invention, any one of the gas pressure of the mixed gas, the heating temperature of the thermionic emission material, and the heating temperature of the substrate, the gas pressure of the mixed gas: less than 150 Torr,
When the heating temperature of the thermionic emitting material is less than 2200 ° C. and the heating temperature of the substrate is less than 300 ° C., a desired high nucleation density and film formation rate cannot be secured, while the gas pressure of the mixed gas is 300 Torr. If the heating temperature exceeds 2,500, the nucleation density and the film formation rate decrease sharply, and the heating temperature of the thermionic emitter increases to 2500.
If the temperature exceeds 100 ° C, the service life of the mixed gas will be extremely reduced, and if the heating temperature of the substrate exceeds 1100 ° C, the synthetic diamond will grow grains and the wear resistance will inevitably decrease. 150 Torr to 300 Torr, the heating temperature of thermionic emission material is 2200 to 2500 ° C, and the heating temperature of the substrate is 300 to 1100 ° C
It was decided.

〔Example〕

Next, the method of the present invention will be specifically described with reference to examples.

The apparatus shown in FIG. 1 is an apparatus for carrying out the method of the present invention. In FIG. 1, 1 is a filament (thermo-electron emitting material), 2 is a base, 3 is a base support, 4 is a reaction furnace, and 5 is a reactor. Heating unit, 6 is a coil or an electrode, 7 is a high-frequency matching box, 8 is a high-frequency power supply, 9 is a gas introduction pipe, 10 is an exhaust device, 11 is a hydrocarbon gas supply device, 12 is a hydrogen gas supply device, 13, 14, 15 and 16 indicate valves respectively.

First, a cemented carbide substrate having a composition of WC-6% by weight Co was prepared. First, as shown in FIG. 1, the substrate 2 was pretreated by immersion in a 5% nitric acid aqueous solution for 20 minutes. Then, H ₂ gas is supplied as a reaction gas from the hydrogen gas supply device 12 into the reaction furnace 4 while the CH ₄ gas is reacted from the hydrocarbon gas supply device 11. The gas is supplied into the furnace 4 to adjust the gas pressure in the furnace to various gas pressures shown in Table 1, and the high frequency power is supplied from the high frequency power supply 8 through the high frequency matching box 7 so that the high frequency power becomes 3 kW. The thermoelectron emitting material 1 composed of a tungsten filament is supplied with electric current and heated so that the surface temperature thereof is also the temperature shown in Table 1, and the base 2 is heated by the heating unit 5 to the temperature shown in Table 1. The methods 1 to 5 of the present invention and the conventional method were carried out by heating, the generation rate of diamond nuclei was measured in a reaction time of 1 hour, and the film thickness and film formation rate of a diamond film formed in a reaction time of 6 hours Was measured.

Further, electron diffraction and laser Raman spectroscopic analysis were performed on the diamond film formed as a result, and all showed a peak peculiar to diamond.

〔The invention's effect〕

From the results shown in Table 1, it is clear that the methods 1 to 5 of the present invention have a higher nucleation density and can form a diamond film at a higher film formation rate than the conventional methods.

As described above, according to the method of the present invention, it is possible to form a diamond film on various tools and wear-resistant members at a high film forming speed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Filament (thermionic emission material), 2 ... Base, 3 ... Base support 4 ... Reactor, 5 ... Heating unit, 6 ... Coil or electrode, 7 ... High frequency matching box, 8 ... ... High frequency power supply, 9 ... Gas inlet tube, 10 ... Exhaust device, 11 ... Hydrocarbon gas supply device, 12 ... Hydrogen gas supply device, 13-16 ... Valve.

Claims (1)

(57) [Claims] When a diamond film is formed on a surface of a tungsten carbide-based cemented carbide substrate by a gas phase synthesis method using a thermionic emission material, a mixed gas of hydrocarbon and hydrogen is used.
In the reactor which generated plasma by high frequency discharge,
The reaction gas introduced under the condition that the gas pressure in the furnace is 150 to 300 Torr and activated by the plasma and the thermoelectron emitting material heated to a temperature of 2200 to 2500 ° C. is 300 to 110
A method for forming a diamond film at a high speed, comprising supplying the solution to the surface of the substrate heated to a temperature of 0 ° C.