JPH04331798A - Method of forming diamond film - Google Patents

Abstract

PURPOSE:To readily form a diamond film having high bond strength to a substrate and excellent roughness degree of surface. CONSTITUTION:A method of forming a diamond film consists of a process of forming a reverse mold having a reverse smooth face of shape opposite to that of a face to be provided with a diamond film of a substrate, a process of forming a smooth layer of hard powder, composed of a compound to be hardly reacted with carbon, on the surface of reverse face, a process of forming a diamond film on the surface of the hard powder layer by vapor phase method, a process of bonding the diamond film to the face to be provided with the diamond film of substrate by brazing or bonding with a synthetic resin and a process of separating the substrate and the reverse mold from the hard powder layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method for easily forming a diamond film with strong adhesion and excellent surface roughness on the surfaces of low-friction, wear-resistant sliding parts and cutting tools by a vapor phase method. It is related to.

0002

BACKGROUND OF THE INVENTION Since diamond is extremely hard and has excellent wear resistance as well as a low coefficient of friction, attempts have been made to apply it to sliding parts and cutting tools.

[0003] A problem when using a diamond film for sliding parts, etc. is that the adhesion of the film to the substrate is low, and if the usage conditions are severe, the film may peel off during use. Diamond films formed by the vapor phase method, which is a traditional diamond film formation method, have poor surface roughness, and the unevenness of the film surface often damages or grinds the mating material.

[0004] In an attempt to increase the adhesion to the substrate, a diamond film is deposited on a substrate such as silicon, on which diamond is relatively easy to precipitate, by a vapor phase method, and the surface side of this diamond film is brazed to the surface of the substrate. However, a method has been proposed in which the substrate is then scraped off (hereinafter referred to as a brazing method). (Unexamined Japanese Patent Publication No. 1-15328). This method is effective when attempting to form a diamond film on the surface of a component containing Fe, Co, or Ni, which is difficult to deposit diamond on. However, methods such as brazing a diamond film formed on the surface of a substrate such as silicon and then scraping off the substrate require a diamond film thickness of 10 μm or more due to grinding accuracy and film strength. There was a problem in that the grinding itself was troublesome and required a great deal of labor and time.

On the other hand, in order to increase the surface roughness of the surface of the diamond film, polishing and the like have hitherto been carried out. The faster the diamond film is formed, and the higher the quality of the film with good crystallinity, the more well-developed euhedral planes (crystal habit planes) become, and the rougher the surface becomes.

[0006] Therefore, in order to make the surface smooth, a considerable thickness must be removed by polishing, laser, or the like.

However, since diamond is extremely hard,
The polishing etc. required a great deal of time and effort. especially,
When it comes to mass producing parts with a diamond film formed on the surface of a shaped object such as a cam consisting of a series of complex curved surfaces at a low cost, it is necessary to minimize the amount of parts removed by polishing or the like.

[0008] Furthermore, when applying a desired abrasion-resistant diamond coating layer to the inner tip of a thin tubular object such as an electric fuel injection nozzle, there is no means for forming the film or for polishing it. is the current situation.

[0009]

[Problems to be Solved by the Invention] It is an object of the present invention to solve the above-mentioned problems.
An object of the present invention is to provide a method for easily forming a diamond film with excellent surface roughness.

0010

[Means for Solving the Problems] The present inventors have focused on the following points regarding the problems of the above-mentioned prior art.

(1) When diamond is deposited on a substrate, a large number of nuclei are generated on the substrate, and the diamond grows horizontally and vertically around the nuclei. Focusing on the fact that it becomes a replica of the shape itself, if you give the substrate a complex shape, it will become the same shape, and at the same time, if you make the surface of the substrate smooth, the surface of the diamond film that will be formed in contact with this surface. A smooth surface similar to the base surface can be obtained, and if this smooth diamond film surface is used as the surface of an actual sliding part, the area of the film surface that needs to be polished can be significantly reduced. I thought.

(2) We also focused on the fact that diamond can be deposited on powders of ceramics such as boron nitride, silicon nitride, and silicon carbide, and created a layer of fine powders of the above ceramics on the surface of the substrate. By intervening and depositing diamond thereon, the diamond film can be easily separated from the ceramic powder portion, and this method can solve the troublesome problem of scraping off the substrate in the brazing method. I thought it could be done.

[0013] In order to improve the brazing method, which has conventionally been used to improve the adhesion between the diamond film and the substrate, the inventors have conducted research based on the above-mentioned points of view, and have completed the present invention. It is something that

The diamond film forming method of the present invention includes the steps of forming an inverted mold having a smooth surface that is in the opposite shape to the shape of the surface of the substrate on which the diamond film is to be formed, and reacting the oppositely shaped surface with carbon. a step of forming a fine hard powder layer made of a compound that is difficult to absorb; a step of forming a diamond film on the surface of the hard powder layer by a vapor phase method; and a step of forming a diamond film on the surface of the substrate. It is characterized by comprising a step of joining by brazing or adhesion with synthetic resin, and a step of separating the base and the reverse mold from the hard powder layer.

[0015]

According to the method for forming a diamond film of the present invention, since the diamond film is firmly bonded to the substrate by brazing or adhesion using synthetic resin, there is no problem such as separation of the diamond film.

Furthermore, the surface of the diamond film formed by this method is extremely smooth, and operations such as surface polishing can be significantly reduced compared to conventional methods. The reason for this is as follows. This method uses an inverted mold with an inverse shape to the surface of the substrate, forms a layer of fine hard powder on the surface of the inverted mold, and forms a diamond film on this powder layer with a smooth surface. do. This is because the reverse mold can then be removed from the hard powder layer portion, and the diamond film surface that was in contact with the smooth surface of the hard powder layer can be used as the surface of the base body.

Furthermore, the substrate can be easily separated from the inverted mold mechanically from the hard powder layer, and there is no need to polish the inverted mold as in the conventional method, so the inverted mold can be separated many times. available,
Particularly in the case of objects with complex shapes, this method can be implemented at low cost in addition to the effect of reducing surface abrasion as described above.

Moreover, by this method, it is possible to form a diamond film on the surface of iron-based parts, which was previously impossible, and in deep areas where it was previously impossible to form a diamond film. It is.

[0019]

【Example】

(Specific Example of the Present Invention) A method for forming a diamond film according to this specific example will be explained step by step.

(1) Step of forming the reverse mold The shape and dimensions of the reverse mold are approximately equal to the shape of the base body, or have a size slightly smaller than the allowance for finishing polishing. In other words, if the part of the substrate where you want to form a diamond film is convex, make the concave part, which is the opposite of the concave part, a little larger considering the thickness of the hard powder layer and the allowance for finishing (Figure 1).
. On the other hand, if the portion of the substrate on which the film is to be formed is concave, the convex portion of the reverse mold is processed to be slightly smaller for the same reason.

The material for the reverse type depends on the shape of the target substrate, but in any case, it is necessary to use a material with high thermal conductivity so that it is possible to control the substrate temperature necessary when depositing a diamond film on the surface. The material is preferably copper, tungsten, or molybdenum for metals, and sintered bodies of silicon carbide, aluminum nitride, boron carbide, etc. for ceramics. For these inverted molds, it is necessary to make the wall thickness of the surface on which diamond is deposited as uniform as possible, and to control the temperature of the deposition surface to be uniform and at a certain level by flowing cooling water on the back side.

However, when methods such as the microwave plasma method and the hot filament method are used, the temperature rise of the substrate is not so much of a problem, and there is no need to pay much attention to the inverted material and cooling structure that will become the substrate. do not have.

[0023] The molding and processing of the reverse mold can be carried out by a general method, and if the material is electrically conductive, electric discharge machining, electrolytic polishing, etc. can be used for the final finishing, while for ceramics etc. The powder can be formed into a near-net shape using a reverse mold, sintered, and then processed and finished using methods such as grinding.

[0024] It is necessary to increase the dimensional accuracy of the reverse mold surface as much as possible. This is necessary in order to reduce the allowance for machining and finishing after the diamond film is finally formed on the desired shape by brazing.

On the other hand, the surface roughness does not require such high smoothness. It is sufficient that it has a certain degree of roughness in order to maintain the hard powder layer formed on the surface of this inverted mold.

(2) Step of forming a hard powder layer (FIG. 1) In order to deposit diamond on the surface of the hard powder layer, the surface roughness of the diamond film in contact with the precipitated hard powder layer is It is determined by the surface roughness of the powder layer. Therefore, the finer the particle size of the powder constituting the hard powder layer, the higher the surface roughness of the diamond contact surface. Therefore, the particle size must be at least 1 μm or less, preferably 0.1 μm or less.

There is basically no problem with the powder material constituting the hard powder layer as long as it is used as a substrate material for conventionally known vapor-phase diamond films. Metals such as silicon, tungsten, molybdenum, and niobium; carbides such as silicon carbide and tungsten carbide; borides such as aluminum nitride, silicon nitride, titanium nitride, and boron nitride; oxides such as aluminum oxide and silicon oxide; and carbon borides. So-called ceramics such as can be used. In addition, diamond powder with an average particle size of 5 nm synthesized by the impact method (product name: Cluster Diamond)
You can also use However, it is undesirable to use a substance that increases the temperature of the inverted mold serving as a substrate during the formation of a diamond film, or that causes thermal decomposition, melting, sintering, or chemical reaction with the material of the inverted mold in that atmosphere.

As mentioned above, since the powder used for the hard powder layer is very fine, submicron, it has very good cohesiveness and does not require a binder except in special cases. A powder layer can be formed.

Usually, the hard powder layer is formed by dispersing the powder in a volatile solvent such as alcohol to form a slurry, coating it by spraying or coating, and drying it. form by

[0030] Furthermore, in order to prevent cracks after drying and improve wettability with the reverse mold, a surfactant or a very small amount of an organic binder such as polyvinyl alcohol (PVA) may be added. .

When using a coating method or the like, if the surface precision of the powder layer cannot be obtained sufficiently, an inverted mold with a mirror-finished surface (the surface shape of the substrate on which the diamond film is formed, It is preferable to improve the precision of the surface by lightly pressing the surface (having dimensions) and transferring the mirror structure.

The material for the reverse mold used in this case does not need to be specified in particular, and as long as it has wear resistance, it can be easily made smooth and with good dimensional accuracy by machining, electrical discharge machining, electrolytic polishing, etc. The material may be selected from the viewpoint of the material from which the surface can be obtained.

[0033] Depending on the three-dimensional shape of the inverted mold, powder may be placed directly on the surface of the inverted mold, and then press molding may be performed using a punch with a surface having the inverted shape of the inverted mold, which is mirror polished. It is also possible to form a powder layer by applying a powder layer.

When it is necessary to increase the mechanical strength of the hard powder layer, it is impregnated with an alkoxide such as silicon or aluminum dissolved in a solvent such as alcohol by a method such as spraying, and then hydrolyzed. It is also effective to fortify it with its products.

However, the various organic materials used to form the hard powder layer with a smooth surface by the above treatment may be harmful when forming the diamond film, so it should be kept in the air after formation. It is desirable to decompose and remove it by heating it at a temperature of about 500°C.

[0036] The thickness of the hard powder layer is 1 mm due to dimensional accuracy.
The following is desirable, and on the other hand, it is better to make it as thin as possible due to the necessity of cooling during formation of the diamond film. Therefore, although the thickness of the powder layer depends on the particle size and thermal conductivity of the fine powder used, it is preferably 100 μm or less. The lower limit cannot be determined unambiguously because the mechanical strength of the layer changes depending on the particle size of the fine powder and the chemical composition that makes up the particles, but the thickness must be approximately 5 times or more the average particle diameter of the powder.
If it is less than this, a good powder layer cannot be obtained.

(3) Diamond film formation process (Fig. 2
) The method of forming a diamond film on the surface of a hard powder layer formed on the surface of an inverted mold by a vapor phase method basically has no problem with any conventionally proposed method.

If this were to be considered a problem, the DC plasma jet method, combustion method, etc., where there is a risk that the hard powder layer and the fine diamond powder that forms the nucleus, which will be described in detail later, may be blown away by the fast gas flow, are not very preferable, but the powder This may not be the case if the formation of the body layer or the adhesion of fine diamond powder is done well.

Furthermore, as mentioned above, it is known that diamond film formation by the vapor phase method involves epitaxial growth on very few substrates such as diamond single crystals and c-BN. Generally, it precipitates and grows as a polycrystalline film through the mechanisms of nucleation and grain growth. Therefore, in order to smooth the contact surface with the substrate, it is desirable to generate a large number of nuclei on the smooth substrate surface, and various means have been proposed to increase the number of nuclei generated. Here, it is preferable to form a thin and uniform layer of ultra-fine diamond powder on a layer formed by solidifying powder in order to create a high density of nuclei. Specifically, a diamond layer is formed by spraying a slurry of cluster diamond dispersed in alcohol or the like so that the surface of the hard powder layer is covered with at least one layer of diamond particles.

The ultrafine diamond used for this purpose is not limited to the above-mentioned cluster diamond, and as long as it is fine, it may be naturally produced or artificially synthesized and crushed without any effect. The diamond used in this case is separated by a water sieve after being crushed, and its particle size is preferably at least finer than the particle size of the powder used for the hard powder layer.

[0041] In addition, in order to make the interface between the core diamond layer and the hard powder layer conform to the surface structure of the hard powder layer, the smoothness can be increased by lightly pressing again with an inverted mold. It is also effective to take measures.

[0042] The thickness of the diamond film deposited on the surface of the inverted mold having a hard powder layer and a core diamond ultrafine powder layer is not particularly limited and varies depending on the use of the final product. In the method of the present invention, there is no problem as long as the thickness is several μm or more. Even if the thickness is several hundred μm or more, separation during film formation can be prevented by selecting the material and particle size of the powder constituting the hard powder layer, and there is no particular problem. In this case, it is best to use a material with a coefficient of thermal expansion as close as possible to that of diamond, such as silicon nitride, and one of the characteristics is that a thick film can be formed relatively easily because the powder layer relieves stress. be.

(4) Brazing step (FIG. 3) The inverted mold with the diamond film formed on its surface is brazed to the surface of the substrate on the diamond surface side. There is no particular problem with the brazing material used here as long as it is a brazing material conventionally used for bonding to diamond tools.

For example, there is no problem with brazing fillers such as Ti-Cu-Ag, and depending on the application, it is also possible to bond with low-temperature solder or epoxy-based synthetic resin in areas where temperature and stress do not apply. be.

[0045] The form of the brazing material may be either foil or powder depending on the shape of the part on which the diamond film will ultimately be formed. In particular, when brazing a surface with a complex shape, it is easier to handle the foil if it is shaped into the shape in advance.

In order to improve the surface accuracy when performing brazing on this base, positioning parts are attached to the base and the reverse mold, or a separate jig for positioning is made, and the brazing material is It is important to apply pressure while melting and brazing it in place. Positioning during this brazing is very important, and the accuracy in this process greatly affects the machining allowance for the final diamond surface, and in some cases, the thickness of the diamond film when deposited. Problems arise such as having to make the film thicker.

(5) Separation step (Figure 4) After brazing, the base and the reverse mold are separated through the hard powder layer, the powder remaining on the diamond surface is mechanically removed, and the diamond surface is finished. By processing, a diamond film can be formed on the target substrate.

Since the hard powder layer is easily destroyed by applying tensile stress, no special equipment is required to separate the base and the reverse mold.

The surface of the brazed diamond has the shape of the surface of the hard powder layer transferred to it, and unlike the euhedral surface on the growing side, it has a very smooth surface. , finishing processing is very easy. Any method combining mechanical grinding, polishing, thermochemical methods, laser, etc. may be used.

(Example 1) Assuming a part with a strong diamond film formed on the sliding surface of a cam-shaped part, a
An attempt was made to form a diamond film on a part of the curved surface of the outer periphery of a 20 mm and 10 mm thick disk (FIG. 5).

[0051] An inverted mold with a thickness of 10 mm and a concave curved surface with a radius 150 μm larger than the final shape was made of stainless steel (SU
S304). The surface roughness of the inverted concave surface is
It was 0.3 μmRz.

A commercially available spray of boron nitride (trade name: Boron Spray) as a release agent was sprayed onto this concave surface to form a hard powder layer with a thickness of about 20 μm.

[0053] This inverted mold was placed in a chamber of a hot filament CVD apparatus, and the molybdenum filament was placed in the vicinity of the center of a semicircular recess with a diameter of 20 mm provided in the inverted mold.

Diamond film formation was carried out under the following conditions.

[0055] CH4/H2 ratio: 0.5, total flow rate: 200 sccm, filament temperature: 2100°C,
Reverse mold surface temperature: 750-800℃, pressure: 50 Tor
r. , Film formation time: 90 hours

The thickness of the polycrystalline diamond film obtained under these conditions was approximately 100 μm, and the surface was (11
1) The surface was well developed.

[0057] For brazing, use JIS standard BAG-8 Cu-
One side of Ti is placed on one side of an Ag-based brazing filler metal with a thickness of 50 μm.
~2wt. %, and the diamond film was set so that this surface was in contact with the diamond film.

[0058] Set the inverted mold at the bottom and the steel disk at the top through the brazing material in a vacuum furnace, and heat to 10-5 Torr.
r. After evacuating to a vacuum, brazing was performed by heating to 950°C.

After cooling, the inverted mold and the diamond film were separated by a layer of boron nitride and polished with emery paper, revealing a diamond surface with a very smooth surface.

In a case like this embodiment, a film can be formed all around at once by using a plurality of inverted molds divided at appropriate parting lines and performing brazing at the same time. (Example 2)

Assuming the formation of a diamond film on the inner surface of the nozzle of a fuel injector for an EFI engine,
An attempt was made to form a diamond film with high surface roughness on the inner tip of a cylindrical tube with an inner diameter of φ5 mm and a length of 100 mm that had a cone-like point (FIGS. 6 and 7).

[0062] In this case, the reverse mold has a diameter of 4.5 mm and a length of 15 mm.
A silicon carbide sintered body with a sharpened tip of 0 mm was used. The surface roughness of the cone-shaped portion at the tip is 1.0μmRz
Finished.

Separately, a slurry was prepared in which a very small amount of PVA was added to ethyl alcohol and silicon nitride having a roughness of 0.3 μm was dispersed therein.

[0064] The tip of the inverted mold was dipped in this slurry, pulled up and dried. Next, stainless steel
304), which has a shape corresponding to the cone-shaped inner tip of the cylindrical base, and whose dimensions take into account the diamond film and brazing thickness, is electrolyzed. Manufactured by polishing. When the slurry applied to the inverted mold has almost completely dried, it is inserted into the inverted mold made of stainless steel (SUS304) with a mirror-finished surface and pressed against the dried slurry to form silicon nitride powder. A hard powder layer was formed by compressing the body layer and at the same time transferring a smooth surface shape of an inverted shape to the surface of the body layer.

On the other hand, a suspension in which cluster diamonds synthesized by the impact method were dispersed in cyclohexane was prepared, and this was sprayed onto the surface of the silicon nitride powder layer. After that, the drying operation was repeated three times to temporarily remove the suspension. The entire surface was covered with ultrafine diamond particles.

A film was formed on the cone-shaped portion of the tip of the inverted mold subjected to the above treatment under the same conditions as in Example 1 for 90 hours by the hot filament method while rotating at a speed of 10 rpm. Incidentally, the thickness of the diamond film measured on another sample formed under the same conditions was approximately 120 μm. (Figure 6)

[0067] The diamond film deposited on the excess portion was mechanically removed to complete a reverse mold with a diamond film formed thereon.

On the other hand, the base material is made of stainless steel (SUS30
Inner diameter φ5m with tapered cone-shaped tip made in step 4)
Silver solder powder containing 1% titanium is placed in the tip of a pipe-shaped object with a length of 100 mm, and then a rod-shaped inverted mold with a diamond film formed thereon is inserted, and then the rod-shaped inverted mold is A steel weight of approximately 200 g was placed on top of the mold.

The whole was placed in a vacuum furnace and heated to 950° C. to completely melt the silver solder, and then cooled.

After cooling, the inverted mold was peeled off from the silicon nitride powder layer and pulled out. (Figure 7)

[0071] The diamond film was brazed at the desired location. It was then polished and finished using a full-sized diamond whetstone made specifically for this purpose.

In this example, a tapered cone type was used, but the effect of this example is that a diamond film can be formed in such a deep part even with a morning glory-shaped type. There is.

(Example 3) An attempt was made to form a diamond film on an object having the same shape as in Example 2.

[0074] In this case, the cone portion at the tip of the inverted mold made of silicon carbide was finished to a mirror finish with diamond abrasive grains. Instead of the hard powder layer made of silicon nitride formed on the surface of the inverted mold, dip the part on the tip of the inverted mold where you want to form a diamond film into a slurry in which cluster diamonds are concentratedly dispersed in cyclohexane. A layer of ultra-fine diamond powder was created. In this case, the thickness of the ultrafine diamond powder layer was set to such a level that the inverted mold serving as the substrate was not exposed.

After sufficiently drying and removing cyclohexane,
As in Example 2, a diamond film was formed for 90 hours by the hot filament method.

[0076] In the subsequent operations, a stainless steel (SUS304) pipe was brazed in the same manner as in Example 2, and the reverse mold was pulled out. In this case as well, when we cut out and examine the part where the cluster diamond layer was easily separated between the layers or on the reverse-shaped surface, and then the film was formed, we found that the diamond film was the target because the surface could be easily smoothed by simple surface polishing. It has been found that it is possible to form on a shaped object.

As described above, it is also possible to use fine diamond powder as the material for the hard powder layer, and in this case, the diamond powder serves as the hard powder layer and the diamond nucleation layer.

[0078] Furthermore, the inverse type of silicon carbide used here did not change at all, and there was no problem in repeated use.

[Brief explanation of drawings]

[Figure 1] Schematic diagram showing an inverted mold with a substrate and hard powder layer formed

[Figure 2] Schematic diagram showing an inverted mold with a substrate and diamond film formed

[Figure 3] Schematic diagram showing the base joined by brazing and the reverse mold

[Figure 4] Schematic diagram showing the inverted mold separated from the base

[Figure 5] Schematic diagram showing the method of forming a diamond film on a substrate assuming a cam

[Figure 6] Schematic diagram showing the method of forming a diamond film on the tip of a pipe-shaped substrate

[Figure 7] Schematic diagram showing the method of forming a diamond film on the tip of a pipe-shaped substrate

[Explanation of symbols]

1 Base 2 Reverse type 3 Hard powder layer 4 Diamond film 5 Brazed part 6 Ultra-fine diamond layer

Claims (1)

[Claims] 1. A step of forming an inverted mold having a smooth surface with an inverse shape to that of the surface on which a diamond film is to be formed on the substrate, and forming a smooth surface made of a compound that does not easily react with carbon on the inversely shaped surface. A step of forming a hard powder layer, a step of forming a diamond film on the surface of the hard powder layer by a vapor phase method, and a step of applying the diamond film to the surface of the substrate on which the diamond film is to be formed by brazing or using synthetic resin. A diamond film forming method comprising a step of joining by adhesion and a step of separating a substrate and an inverted mold from a hard powder layer.