JPH07108831B2 - Diamond coated components - Google Patents

Description

The present invention relates to a diamond-coated member, and more particularly to a diamond-coated member that can be widely used for various cutting tools such as turning tools, end mills, cutters, drills, etc., and various wear-resistant members.

[Background Art] Conventionally, when manufacturing cutting tools, etc., ceramics (made
The surface of the substrate is coated with a diamond film, but the adhesion of the diamond film is insufficient, so chipping of the cutting edge occurs when cutting is performed.

To further explain this, for example, Japanese Patent Publication No. 60-59086, Japanese Patent Publication No. 61-109628, and Japanese Patent Publication No. 61-291493 disclose techniques for using silicon nitride substrates or ceramic substrates with a specific thermal expansion coefficient to obtain diamond coating materials with good adhesion.

However, these are all after the diamond coating is formed.
This method prevents the diamond film from peeling off by suppressing the thermal stress that occurs during cooling, but its adhesion is still insufficient.

This is evidenced by the fact that when cutting is performed using a diamond-coated tip, chipping of the cutting edge is still observed.

The object of the present invention is to eliminate such chipping by:
The present invention provides a diamond-coated member in which the adhesion of a diamond film to a substrate is sufficiently high and which can be easily produced.

DISCLOSURE OF THE INVENTION The diamond-coated member of the present invention is characterized by having a diamond film formed on the surface of a ceramic substrate containing columnar grains with a minor axis of 0.2 to 1 μm and an aspect ratio of 2 or more at an areal density of 30% or more.

[Best Mode for Carrying Out the Invention] The present invention is described in detail below.

Ceramic substrate The ceramic substrate in the present invention has a surface having a minor axis.
Columnar grains having an aspect ratio of 2 or more, preferably 3 or more, more preferably 4 or more, with a surface density of 30
% or more, preferably 40% or more.

However, the minor diameter, aspect ratio and content of the columnar particles mentioned here are determined by polishing the surface of the substrate to form a mirror surface, etching it with phosphoric acid, photographing it with a scanning electron microscope, and then image processing the photograph to obtain a 2D image.
It can be found by dimensional analysis.

Here, the surface density is a value obtained by distinguishing the area occupied by the columnar grains from the other areas within the obtained fixed area, totaling the areas occupied by the columnar grains, and dividing this total area by the fixed area.

Therefore, since the columnar particles are considered to be present randomly, the minor axis and aspect ratio of the columnar particles are values that take into account particles that are lying on their side or obliquely.

In the present invention, the surface of the ceramic substrate is provided with a particle having a minor axis of 0.2 mm.
Columnar particles with an aspect ratio of 2 or more and a surface density of 1 μm or less
The reason why the adhesion of diamond film improves when the ratio is more than 30% has not been theoretically elucidated.However, the inventors presume that the surface of ceramic substrate is caused by columnar grains, and at the initial stage of diamond formation, the grain boundary of ceramic substrate is etched by the atmospheric gas of CVD, and columnar grains protrude, and then these columnar grains penetrate into the diamond film formed on it as if they were anchors, and as a result, the contact area between diamond and ceramic substrate surface increases significantly, and the adhesion of diamond film to ceramic substrate surface increases, and the peeling strength of diamond film increases.

If the minor axis of the columnar particle is less than 0.2 μm, the strength of the columnar particle itself is insufficient, and even if this particle and the diamond film described later are intertwined, the columnar particle side will be broken, so the adhesion of the diamond film is insufficient.On the other hand, if the minor axis of the columnar particle is more than 1 μm, the effect of increasing the contact area between this particle and the diamond film may be reduced.In addition, if the aspect ratio of the columnar particle is less than 2, the holding force of the columnar particle on the surface of the substrate is weak, and the columnar particle does not protrude sufficiently onto the substrate surface, so the effect of increasing the contact area may not be obtained.Furthermore, if the content of columnar particle is less than 30%, the above effect is reduced, and the adhesion of the diamond film may be insufficient.

The ceramic substrate in the present invention can be formed from, for example, oxide-based fine ceramics such as alumina, zirconia, mullite, and spinel; non-oxide-based fine ceramics such as silicon carbide, silicon nitride, boron nitride, boron carbide, aluminum nitride, and sialon; and ceramics in which silicon carbide whiskers, silicon nitride whiskers, carbon whiskers, etc. are dispersed in the fine ceramics.

Among these, a ceramic substrate formed mainly of silicon nitride is preferred.

_{A preferred ceramic substrate is a sintered body obtained by sintering a composition containing silicon nitride as the main component and at least one sintering aid selected from the group consisting of ZrO2, MgO, Al2O3, and Y2O3 or their precursors .}

A more preferred ceramic substrate is a sintered body obtained by sintering a composition containing silicon nitride ceramic as the main component and a sintering aid consisting of _ZrO2 and _MgO , or a sintering aid consisting of _Al2O3 and _{Y2O3 .} Note that precursors of the sintering aid, such as sulfates, carbonates, and halides, which can be converted to oxides during sintering, can also be used as suitable sintering aids.

The content of the sintering aid in the composition varies depending on the type of sintering aid and cannot be determined in general, but generally speaking, it is 2 to 20 wt % in terms of oxide, and preferably 3 to 16 wt %. If the content of the specific sintering aid is less than 2 wt %, the sintered body may not be dense even after sintering, and if the content exceeds 20 wt %, the crystal grains may grow significantly during sintering, making it impossible to form the desired columnar grains.

The sintering temperature varies depending on the type of sintering aid, but is usually
The sintering temperature is 1,550 to 1,850°C, preferably 1,570 to 1,830°C. If the sintering temperature is less than 1,550°C, the columnar grains may not grow sufficiently, whereas if the sintering temperature exceeds 1,850°C, the diameter of the columnar grains may become too large, making it impossible to obtain columnar grains of the desired shape.

As the sintering atmosphere, a nitriding gas or a mixed gas of an inert gas such as nitrogen and argon, which does not decompose silicon nitride during sintering, is used.

The gas pressure during sintering varies depending on the sintering temperature, but is usually 10 to 300 kg/cm ² , and a pressure sufficient to control the decomposition of silicon nitride occurring during sintering is preferred.

This sintering method, combined with the action of the sintering aid, allows the columnar grains defined in the present invention to be uniformly precipitated in the sintered body with almost no decomposition of silicon nitride, and this method makes it easier to increase the content of the columnar grains compared to simply mixing the columnar grains with ceramics.

Diamond Film In the present invention, a diamond film is formed on the ceramic substrate. Here, the diamond film is a broad concept that includes diamond, diamond-like carbon, and films containing diamond and diamond-like carbon.

The diamond film can be formed by any known diamond film forming method, but it is practically preferable to use a vapor phase method.

Specifically, a preferred method is to form the coating film on the ceramic substrate by contacting the gas obtained by exciting a raw material gas containing a carbon source gas with the ceramic substrate in a reaction chamber.

The source gas may be any gas containing at least a carbon source gas, and is preferably a gas containing carbon atoms and hydrogen atoms.

Specifically, the source gas may be, for example, a mixed gas of a carbon source gas and hydrogen gas.

If desired, a carrier gas such as an inert gas may be used together with the source gas.

As the carbon source gas, various gases such as hydrocarbons, halogen-containing compounds, oxygen-containing compounds, and nitrogen-containing compounds can be used.

Examples of hydrocarbon compounds include paraffinic hydrocarbons such as methane, ethane, propane, and butane; olefinic hydrocarbons such as ethylene, propylene, and butylene; acetylenic hydrocarbons such as acetylene and allylene; diolefinic hydrocarbons such as butadiene; alicyclic hydrocarbons such as cyclopropane, cyclobutane, cyclopentane, and cyclohexane; and aromatic hydrocarbons such as cyclobutadiene, benzene, toluene, xylene, and naphthalene.

Examples of halogen-containing compounds include halogenated hydrocarbons such as halogenated methane, halogenated ethane, and halogenated benzene, and carbon tetrachloride.

Examples of oxygen-containing compounds include ketones such as acetone, diethyl ketone, and benzophenone; alcohols such as methanol, ethanol, propanol, and butanol; ethers such as methyl ether, ethyl ether, ethyl methyl ether, methyl propyl ether, ethyl propyl ether, phenol ether, acetal, and cyclic ethers (dioxane, ethylene oxide, and the like); ketones such as acetone, pinacoline, methyl oxide, aromatic ketones (acetophenone, benzophenone, and the like), diketones, and cyclic ketones; aldehydes such as formaldehyde, acetaldehyde, butyraldehyde, and benzaldehyde; organic acids such as formic acid, acetic acid, propionic acid, succinic acid, butyric acid, oxalic acid, tartaric acid, and stearic acid; acid esters such as methyl acetate and ethyl acetate; dihydric alcohols such as ethylene glycol and diethylene glycol;
Examples include carbon monoxide and carbon dioxide.

Examples of the nitrogen-containing compound include amyls such as trimethylamine and triethylamine.

The carbon source gas may be any of petroleum gases such as gasoline, kerosene, turpentine, camphor oil, and pine oil, heavy oils, gear oil, and cylinder oil, or a mixture of the above carbon compounds.

Among these carbon source gases, paraffinic hydrocarbons such as methane, ethane, and propane, which have a high gas or vapor pressure at room temperature; ketones such as acetone and benzophenone; alcohols such as methanol and ethanol; and oxygenated compounds such as carbon monoxide and carbon dioxide gas are preferred.
Carbon monoxide is particularly preferred.

There are no particular limitations on the hydrogen gas used, and it is possible to use, for example, hydrogen gas obtained by gasifying petroleum, converting natural gas or water gas, electrolysis of water, reaction of iron with steam, complete gasification of coal, etc., which has been sufficiently purified.

When the hydrogen constituting the hydrogen gas is excited, it forms atomic hydrogen.

This atomic hydrogen has the effect of removing non-diamond components such as graphite and amorphous carbon that are precipitated simultaneously with the deposition of diamond.

The means for exciting the raw material gas may include, for example, microwave plasma CVD, RF plasma CVD, DC plasma CVD, etc.
method, organic field plasma CVD method, hot filament method, thermal CVD
Examples of the deposition methods include a photo-CVD method, a combustion flame method, and a sputtering method.

Among these, various plasma CVD methods are preferred.

Of the combinations of the source gases and excitation means mentioned above, the combination using a mixed gas of carbon monoxide gas and hydrogen gas and microwave plasma method is particularly preferred for the purposes of the present invention.

In other words, when this mixed gas is excited by microwaves, the excited gas precipitates diamond on the surface of the substrate, and diamond crystals grow using the grain boundaries on the surface as nuclei, which is thought to effectively improve the adhesion of the diamond film.

In the gas phase method, the temperature of the substrate on which the diamond film is formed varies depending on the excitation method of the raw material gas and cannot be determined in general, but when coating a crystalline diamond film, the temperature is usually 300 to 1200°C, preferably 400 to 1,100°C.

If the temperature is lower than 300°C, the diamond deposition rate will be slow and the crystallinity and homogeneity of the precipitate will be lost.

On the other hand, if the temperature is higher than 1,200℃, the effect will not be commensurate with the increase, and it will be disadvantageous in terms of energy efficiency.
The diamond formed may be etched away.

The reaction pressure during the formation of the diamond film is usually 10 ⁻⁶ to ^{10 −3} torr, preferably 10 ⁻⁵ to 800 torr.
If the reaction pressure is lower than 10 ^-6 torr, the diamond deposition rate slows or even stops, while if it is higher than 10 ^-3 torr, the amount of graphite produced increases.

The reaction time cannot be determined in general terms because it differs depending on the surface temperature of the substrate, the reaction pressure, the required film thickness, etc., and may be determined appropriately.

There is no particular restriction on the thickness of the diamond film thus formed, but it is usually about 0.5 to 100 μm, preferably 1 to 60 μm.

Diamond-Coated Member The diamond-coated member thus obtained has excellent adhesion of the diamond film and does not easily peel off from the substrate.

The present invention will now be described in more detail with reference to examples.

(Examples 1 to 5, Comparative Examples 1 to 5) _{Si3N4 powder} with an average particle size of 0.7 μm (BET specific surface area of 10 ^m2 /g),
0.4 μm MgCO ₃ powder, 0.2 μm ZrO ₂ powder, 2 μm
Y ₂ O ₃ powder of 1 μm and Al ₂ O ₃ powder of 1 μm were mixed to the ratio and composition shown in Table 1, and the mixture was milled for 16 hours using ethanol as a medium and a pot mill and balls made of Si ₃ N _4.
The materials were wet mixed for 1 hour. After mixing, the mixture was dried, and the resulting raw material mixture was pressed in a mold at a pressure of 1.5 ton/ ^cm² . The pressed product was sintered under the conditions shown in Table 1. The sintered product was ground to obtain silicon nitride chips (SPGN421) having columnar grains as shown in Table 1.

This silicon nitride chip was used as a substrate and placed in the reaction chamber of a microwave plasma CVD apparatus.

The substrate temperature was 1,000°C, the pressure was 50 torr, and the flow rate of the raw material gases into the reaction chamber was 20 sccm of carbon monoxide gas and 20 sccm of hydrogen gas.
The flow rate was set to 80 sccm, the microwave output was set to 300 W, and the reaction was carried out for 5 hours to obtain a film-like deposit having a thickness of 10 μm on the substrate.

When we performed Raman spectroscopy on this deposit,
The Raman scattering spectrum showed a peak at around 1333 cm ^-1 due to diamond, confirming that the diamond was almost free of impurities.

The obtained diamond-coated tip was subjected to a cutting test under the following conditions, and then the cutting edge was observed under a scanning electron microscope (SEM). After 10 minutes of cutting test, the tip of the example was found to have almost no diamond film peeling off and almost no wear. Furthermore, the average cutting time until the diamond film peeled off from the tip after repeated cutting tests is shown in Table 1.

Work material: Al-8 wt% Si alloy Cutting speed: 800 m/min Feed: 0.1 mm/rev Depth of cut: 0.25 mm In all examples, the cutting speed was 1,500 m/min
Even when the material was changed to in, no peeling occurred in the 10-minute cutting test.

(Comparative Example 6) On the other hand, for comparison, an α-sialon ceramic (spherical particles, average particle size: 1 μm) consisting of columnar particles was used.
A cutting test similar to that in Example 1 was carried out using a tip formed by coating a diamond film (thickness 10 μm) on a substrate made of a diamond alloy (diamond alloy) in the same manner as in Example 1.
After a minute of testing, the diamond coating began to peel off.

[Industrial application field] The diamond-coated member of the present invention has a diamond film coated on a specific ceramic substrate, so the adhesion of the diamond film is excellent, and when used in, for example, cutting tools, chipping and peeling do not occur, and wear is also resistant. Therefore, the life of the tool can be extended. Furthermore, the substrate can be manufactured using a gas pressure sintering method, and the diamond film can be formed using a vapor phase method, so the product can be easily manufactured.

As described above, the present invention provides tools such as cutting tools, end mills, cutters,
This will make an important contribution to the fields of cutting tools such as drills and various wear-resistant materials.

──────────────────────────────────────────────────── Continued from the front page (72) Inventor: Shoichi Watanabe 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Prefecture NGK Spark Plug Co., Ltd. (72) Inventor: Satoshi Iio 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Prefecture NGK Spark Plug Co., Ltd.

Claims (9)

[Claims] 1. A diamond-coated member comprising a ceramic substrate having a surface containing columnar grains with a minor axis of 0.2 to 1 μm and an aspect ratio of 2 or more in an areal density of 30% or more on the surface thereof, and a diamond film formed on the surface thereof. 2. The ceramic substrate according to claim 1, wherein the ceramic substrate is a sintered body obtained by using silicon nitride as a main raw material. [Claim 3] In claim 1, the ceramic substrate is a sintered body formed from silicon nitride and at least one sintering aid selected from the group consisting of ZrO ₂ , MgO, Al ₂ O ₃ and Y ₂ O ₃ or precursors thereof. 4. The sintered body according to claim 3, wherein the main component is silicon nitride, and the auxiliary components are MgO+ZrO ₂ , MgO+Y ₂ O ₃ , and Al ₂ O ₃
+ ZrO ₂ , Al ₂ O ₃ + Y ₂ O ₃ combination. 5. The method according to claim 3, wherein the content of said sintering aid is 2 to 20% by weight in terms of oxide. 6. The method according to claim 2, wherein the sintered body is 1,
It is sintered in nitrogen gas or a mixture of nitrogen gas and an inert gas at a sintering temperature of 550 to 1,850°C and a pressure of 10 to 300 kg/ ^cm2 . 7. A method according to claim 1, wherein the thickness of the diamond film is 0.5 to 100 μm. 8. A method according to claim 1, wherein the thickness of the diamond film is 1 to 60 μm. 9. The diamond coating of claim 1.