JPH02122075A - Coating method with hard carbon film - Google Patents

Abstract

PURPOSE:To coat a metal substrate with a hard carbon film with high bonding strength by successively subjecting the substrate to carburization and treatment with hydrogen plasma before coating with the hard carbon film. CONSTITUTION:A metal substrate made of a metal belonging to the group IIIA, IVA, VA, VIA, VIIA or VIIIA of the periodic table or an alloy thereof is ion-carburized and the surface of the substrate is treated with hydrogen plasma. The substrate is then coated with a hard carbon film contg. 5-30atomic% hydrogen by vapor phase synthesis with a hydrocarbon compd. such as methane as starting material. The metal substrate is coated with the hard carbon film with satisfactory bonding strength and wear resistance, lubricity and corrosion resistance are rendered to the substrate.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of coating a metal substrate with a hard carbon film, thereby imparting properties such as wear resistance, lubricity, and corrosion resistance to the object. It is intended to give.

[Prior Art] Hard carbon films have a hardness comparable to that of diamond, and have excellent wear resistance, lubricity, and corrosion resistance, so they are eagerly awaited for various uses. When coated directly onto a metal substrate, the film's original excellent properties have not always been utilized because of problems with its adhesion. For example, as shown in the Abstracts of the 2nd Diamond Symposium, page 93 (1987), hard carbon films are made of metals that form highly covalent bonds with carbon, such as silicon and tungsten. The material can be directly coated with a hard carbon film to form a highly adhesive coating, but does not form a covalent bond with the carbon.
When using metals belonging to Group IIIA, IVA, VA, VTA, ■A1■A, or their alloys as a base material, the conventional method of directly coating with a hard carbon film has problems in terms of hardness and resistance. It has been difficult to coat with a hard carbon film that has excellent abrasion resistance, lubricity, and corrosion resistance, and has strong adhesion to the substrate.

[Problems to be Solved by the Invention] The object of the present invention is to develop a new method for coating a metal substrate with a hard carbon film having good adhesion.

[Means and actions to solve the problem] The gist of the present invention is as follows.

(1) A method for coating a hard carbon film, which comprises carburizing a metal base material, then subjecting the surface of the base material to hydrogen plasma treatment, and then coating the base material with a hard carbon film.

(2) The method for coating a hard carbon film according to item 1 above, wherein the carburizing method for the metal base material is an ion carburizing method.

The hard carbon film referred to in the present invention is as follows. The elemental composition is mainly carbon, and it has a hardness similar to that of natural diamond.It is amorphous and shows a halo pattern in its electron diffraction image. The Raman spectrum shows broad peaks characteristic of amorphous materials near 1580 cm-' and 1360 cm-'. When a thin film of hard carbon is observed with a scanning electron microscope under magnification of about io, ooo times, it is a uniform and smooth film with no grain boundaries observed. Hard carbon is generally produced by a gas phase synthesis method using hydrocarbon compounds as raw materials, and is approximately 4Qat.
Contains less than om% hydrogen. It is thought that hydrogen enters the dangling bonds of carbon atoms, stabilizing the amorphous state and creating a highly hard structure.

It is presumed that the presence of an appropriate amount of hydrogen causes hard carbon to exhibit high hardness comparable to that of natural diamond. If there is too much hydrogen in the hard carbon film, it becomes a soft organic film.

Therefore, in the hard carbon film of the present invention, the proportion of hydrogen in the film is 35 aton+% or less, preferably 5 to 30 aton+%.
m% is suitable.

The method for forming the hard carbon film used in the present invention is disclosed in JP-A-59-174507, JP-A-59-174507, An ionized vapor deposition method as disclosed in Japanese Patent No. 59-174508 and the like is preferred.

FIG. 1 shows a diagram of the principle of the ionization vapor deposition apparatus. Hydrocarbon gas, which is a raw material for a hard carbon film, is introduced under reduced pressure, ionized by glow discharge and red-hot filament 3, and extracted by the expanding magnetic field of electromagnet 4. This part covered with electromagnets is called the ion source. The extracted ions are accelerated toward the base material l to which a negative bias voltage is applied, collide with the base material, and are deposited. As the raw material gas, hydrocarbons that can be easily introduced as a gas such as methane, ethane, acetylene, and benzene may be used, and among them, methane is preferred. Hydrogen gas may be used as a diluent gas for the above-mentioned raw material gas. The pressure inside the container is
Since it is necessary to generate plasma and accelerate ions, 1 x 10-6 Torr to I Torr is sufficient, but in terms of film quality and film formation rate, I x 10-'T
orr to I x 10-'Torr is desirable. A good thin film is formed when the temperature of the base material is from room temperature (about 25"C) to 600°C. Within this range, a particularly preferable range is room temperature (about 25"C) to 300°C. When the material temperature is higher than 600°C, the film created tends to become graphite-like, and even if a hard carbon film is formed, if it is left to cool to room temperature, residual heat between the base material and the film will be lost. Since the stress is large, the film is likely to peel off during subsequent use.The bias voltage between the substrate and the ion source is 50V to -1500V, especially 1500V to 11000V.
is the preferred range. When hydrocarbon ions are accelerated by a bias voltage and collide with a base material, the C14 bonds of the colliding ions are broken due to the collision energy, and hydrogen atoms are ejected. The amount of hydrogen atoms ejected depends on the kinetic energy of the colliding ions, that is, the bias voltage; if the bias voltage is too low, a soft, organic film with a large amount of hydrogen tends to form, whereas if the bias voltage is too high, a graphite-like film tends to form. Furthermore, self-sputtering of the film occurs, and the film formation rate decreases.

The magnetic flux density in the ion source is suitably in the range of 100G to 100OG, and more preferably in the range of 300G to 500G. The detailed manufacturing conditions vary depending on the arrangement of the gas inlet in the device, the size of the ion source, the position of the substrate, etc., and therefore it is desirable to set optimal conditions as appropriate.

The metal substrates targeted by the present invention are II[A, TVA, V
Metals belonging to the A, VIA, ■A, and ■A groups, or alloys thereof, which are difficult to form covalent bonds with carbon and can be carburized, such as Zr, Ta, and MoXFe.

Any Co, Ti, etc. can be used, but iron, cobalt, etc. are important from a practical standpoint.

In implementing the present invention, carburizing treatment, hydrogen plasma treatment, and hard carbon film coating may be performed in the following order. First, the target metal base material is carburized.
At this time, it is better to carburize the surface layer of the metal base material as much as possible (a thin layer of carbon may be formed on the surface of the metal base material, but There is no problem in moving on to the next hydrogen plasma treatment.

As the carburizing method used in the present invention, conventionally used methods such as gas carburizing method and molten salt carburizing method can be used. In addition, by placing the base material at a high temperature in a container with an atmosphere in which hydrocarbon gases such as methane and ethane are decomposed and ionized, the base material is carburized and at the same time, the surface of the base material is also Ionic carburization methods can be used to form a thin film of carbon. From the viewpoint of film adhesion during the formation of a hard carbon film in the subsequent process, the ion carburizing method is capable of carburizing a large amount of the base material and forming a carbon (W) film on the surface of the base material.
In order to coat with a hard carbon film that has excellent bonding properties with carbon on the surface film and strong adhesion, it is desirable to apply the ion carburization method.

Next, the metal base material that has been carburized in this way is subjected to hydrogen plasma treatment. The hydrogen plasma treatment performed in the present invention refers to hydrogen plasma generated by a plasma CVD apparatus such as that described in Japanese Patent Publication No. 62-120 or a plasma CVD apparatus disclosed in Japanese Patent Application Laid-Open No. 59-174507. , how to leave Motozuki alone, and JP-A-61-122
This method includes a method of irradiating hydrogen plasma species using an ion beam device, an ion implantation device, or the like as shown in Japanese Patent No. 197. For wood, any method may be used as long as it allows hydrogen atoms and hydrogen ions produced by the decomposition of hydrogen molecules to collide with the base material at high speed using heat or an electromagnetic field.

After this, the hard carbon film formation process described above is performed.

In these series of carburizing, hydrogen plasma treatment, and hard carbon film formation, if the surface is not exposed to the atmosphere during the process, gases such as oxygen will be adsorbed onto the surface, reducing the adhesion of the hard carbon film. Continuous processing under vacuum is desirable.

In the method of the present invention, the mechanism by which a hard carbon film with strong adhesion can be coated is not necessarily clear, but it is thought to be as follows.

In other words, by first carburizing the base material and forming a carbon-rich layer on the surface layer of the base material, the difference between the carbon carburized on the base material and the hard carbon coated on the surface is created. It is thought that a strong bond can be formed between the two. If the base material is not carburized, it is thought that only the bond between the metal base material and carbon exists at the interface between the base material and the hard carbon film, and generally there is a strong bond between the metal material and carbon. This method does not produce a film with good adhesion. Furthermore, in the present invention, it is thought that adhesion between the hard carbon film and the carbon layer is improved by activating the surface layer by performing hydrogen plasma treatment in advance.

[Example Example 1 Pure iron with a thickness of 51 nIn (99
, 99%) on the plate, the surface equilibrium carbon concentration of the gas on the sample surface is 0.
．． Gas carburizing was performed using methane gas under the following conditions: 9%, carburizing temperature: 930'C, and carburizing time: 1 hour. As a result, it was confirmed by analyzing the cross section of the sample with an electron beam probe microanalyzer that carburization had proceeded into the pure iron to a depth of approximately 1 mm from the surface.

Next, using hydrogen gas as a raw material on the surface of this sample, the atmospheric pressure I
10”” Torr, base material bias voltage -1000V,
Substrate temperature 300 °C, ionic current 2 mA/cf,
Hydrogen plasma irradiation was performed for 30 minutes under these conditions. Thereafter, by using ionization vapor deposition method, methane gas was used as a raw material to create an atmospheric pressure I.
X 10-2 Torr, substrate bias voltage -800
v, substrate temperature 300°C, ionic current 2+nA/c++
As a result of vapor deposition for 60 minutes under the conditions of 1, a hard carbon film with a thickness of about 1 μm was uniformly coated with a surface as smooth as the surface of the base material and without peeling. The hydrogen content of this film is 2
The electron beam diffraction image showed a halo pattern. The Raman spectrum showed broad peaks near 1580 cm-' and 1360 cm-'. Even when the surface of the coated sample was scratched with a 9H pencil, no peeling or scratching of the film occurred. Similarly (when scratched with a stainless steel Vincent, grooves were formed. This was because the iron base material was plastically deformed and indented into the groove shape. Even in this case, no peeling of the hard carbon film was observed.

Example 2 A temporary mirror-finished surface of pure iron (99.99%) with a thickness of 5 mm was coated with ion carburization using methane gas as a raw material at a pressure of I x 10-”Torr and a base material bias voltage of -100.
0■, base material temperature 760°C, ion electric current B2mA/c+f
The vapor deposition was carried out for 10 minutes under the conditions of 1, and carburization was performed. As a result, a graphite film with a thickness of about 0.08 ttm was deposited on the surface of the base material at the same time as carburizing. Due to the high base material temperature, approximately 0,
It was confirmed by analyzing the cross section of the sample with an electron beam probe microanalyzer that carburization had proceeded into the pure iron over a depth of 5 mm.

Next, on this sample surface, using hydrogen gas as a raw material, the atmospheric pressure lx 10
Hydrogen plasma irradiation was performed for 60 minutes under the following conditions: -''Torr, substrate bias voltage -1000V, substrate temperature 300'C, and ion current 'l mA/ctB.As a result, the surface carbon was modified to hard carbon by Raman scattering spectroscopy. Furthermore, using the IsN resonance nuclear reaction method, it was found that hydrogen was present at a depth of about 8 to 2 atom% from the surface to a depth of about 0.05 mm.
It has been confirmed that it exists.

Thereafter, using methane gas as a raw material, an atmospheric pressure of I x 10-''Torr, a substrate bias voltage of -800cm, a substrate temperature of 300°C, and an ion current of 2m were further applied using an ionization vapor deposition method.
The hard carbon film was coated for 60 minutes under the conditions of A/c+fl. The hydrogen content of this film was 27 atom%, and the electron beam diffraction image showed a halo pattern.

The Raman spectrum is around 1580cnr' and 1360cnr'
A broad peak was observed near an-'.

This sample has a smooth surface equal to the base material surface, and -
It was coated like that. Even when this surface was scratched with a 9H pencil, no peeling or scratching of the film occurred. When scratched with the same stainless steel bottle set, grooves were formed. This is because the iron base material undergoes plastic deformation and becomes groove-shaped.
Even in this case, no peeling of the hard carbon film was observed.

Example 3 A mirror-finished surface of a cobalt (99.99%) plate with a thickness of 6 mm was coated with ion carburization using methane gas as a raw material at an atmospheric pressure of I x 10-” Torr and a material bias voltage of 1.
000V, material temperature 800°C, ion current 3m^/c
+d for 10 minutes, and carburization was performed. As a result, a graphite film about 0.09 μm thick was deposited on the surface of the base material simultaneously with carburization. Due to the high base material temperature, approximately 0.0 mm is removed from the interface.
It was confirmed by analyzing the cross section of the sample with an electron beam probe microanalyzer that the carburization was extending into the cobalt over a depth of 6 mm.

Next, the atmospheric pressure IX I is applied to this sample surface using hydrogen gas as a raw material.
Hydrogen plasma irradiation was performed for 60 minutes under the following conditions: O-'' Torr, substrate bias voltage -1000V, substrate temperature 300°C, and ion current 3mA/c+d.As a result, the surface carbon was modified to hard carbon by Raman scattering spectroscopy. It was found that 7 to 2 atom% of hydrogen was present at a depth of approximately 0.05 μm from the surface using Saraban-5N resonance nuclear reaction method.
It has been confirmed that it exists.

Thereafter, the ionization vapor deposition method was performed using methane gas as a raw material at an atmospheric pressure of I x 10-2 Torr, a base material bias voltage of -800 cm, a base material temperature of 300'C, and an ion conductor. A
The hard carbon film was coated for 60 minutes under the conditions of 3 m/a+1. The hydrogen content of this film is 25 atoms
%, and the electron beam diffraction image showed a halo pattern.

In the Raman spectrum, it is around 1580 cm-' and 1360 cm-'.
A broad peak was observed near c+n-'.

This sample has a smooth surface equal to the base material surface, and -
It was coated like that. Even when this surface was scratched with a 9H pencil, no peeling or scratching of the film occurred. When scratched with the same stainless steel bottle set, grooves were formed. This is because the cobalt base material was plastically deformed and recessed in the shape of a groove, and even in this case, no peeling of the hard carbon film was observed.

Example 4 The mirror-finished surface of a fJ-12% cobalt-15% molybdenum alloy plate with a thickness of 10 mm was coated with an air pressure of I x 10-zTorr using methane gas as a raw material by ion carburizing.
Base material bias voltage -1000V, base material temperature 700°C,
Vapor deposition was performed for 10 minutes at an ionic current of 2 mA/cni,
Carburizing was performed. As a result, a graphite film about 0.08 μm thick was deposited on the surface of the base material simultaneously with carburization. It was confirmed by analyzing the cross section of the sample with an electron beam probe microanalyzer that carburization progressed into the alloy to a depth of approximately 0.6 mm from the interface due to the high base material temperature.

Next, the sample surface is heated to an atmospheric pressure of IX 10 using hydrogen gas as a raw material.
Hydrogen plasma irradiation was performed for 60 minutes under the following conditions: -3 Torr, substrate bias voltage -too much V, substrate temperature 300"C, and ion current 3 mA/c+fl. As a result, the surface carbon was modified into hard carbon by Raman scattering spectroscopy. It was found that approximately 0
．． It was confirmed that 8 to 2 atom% of hydrogen existed over a depth of 0.05 μm.

Thereafter, using methane gas as a raw material, an atmospheric pressure of I x 10-''Torr, a substrate bias voltage of -800V, a substrate temperature of 300'C, and an ion current of 3
mA/co! The hard carbon film was coated for 60 minutes under the following conditions. The hydrogen content of this film is 26 atom%
The electron diffraction image showed a halo pattern.

In the Raman spectrum, it is around 1580 cm-' and 1360 cm-'.
A broad peak was observed near c+n-'.

This sample has a smooth surface equal to the base material surface, and -
It was coated like that. Even when this surface was scratched with a 9H pencil, no peeling or scratching of the film occurred. When scratched with tweezers also made of zirconia ceramics, a groove was created. This is because the base alloy was plastically deformed and recessed in the shape of a groove, and even in this case, no peeling of the hard carbon film was observed.

In addition, in Examples 1.2.3 and 4, when carburization and hydrogen plasma treatment were not performed, all films peeled off.

[Effect of the invention 1] The present invention enables a hard carbon film with excellent lubricity, wear resistance, and corrosion resistance to be applied to various materials such as iron, cobalt, or alloys thereof, which have been difficult to coat directly. It has become possible to coat metal materials with strong adhesion, opening up applications as lubricious coatings and anti-wear coatings.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of an ionization vapor deposition apparatus. ■ is the base material,
2 is a grid, 3 is a filament, 4 is an electromagnet, and 5 is a raw material gas introduction pipe.

Claims (2)

[Claims] (1) A method for coating a hard carbon film, which comprises carburizing a metal base material, then subjecting the surface of the base material to hydrogen plasma treatment, and then coating the base material with a hard carbon film. (2) The method of coating a hard carbon film according to claim 1, wherein the method of carburizing the metal substrate is an ion carburizing method.