JP7302878B2 - Carbon film and sliding member - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon film and a sliding member.

Sliding members that slide in lubricating oil are used in various machines, for example, in internal combustion engines such as automobiles. Such sliding members are required to be able to withstand use in harsher environments, and are required to have, for example, high wear resistance and low friction properties. As such a sliding member, a member having a diamond-like carbon (DLC) film (hereinafter also simply referred to as “carbon film”) on its surface is known. A member having a base material and a hard carbon film formed on the surface of the base material via an intermediate layer is known as the sliding member. The hard carbon film is a so-called DLC film, which is defined by a specific ratio of sp ³ bonds in carbon interatomic bonds, a specific hydrogen content, and the like (see, for example, Patent Document 1).

JP 2019-116677 A

In recent years, sliding members are required to operate stably in harsher environments. Depending on the environment in which the sliding member is expected to operate, the sliding member may be required to have even higher wear resistance and low friction. As described above, the sliding member having the carbon film has room for further study from the viewpoint of further improvement in wear resistance and low friction properties.

An object of the present invention is to provide a carbon film and a sliding member that are excellent in wear resistance and low friction in high-speed sliding at a sliding speed exceeding 1 m/s in oil.

In order to solve the above problems, a carbon film according to one aspect of the present invention is a carbon film composed of carbon atoms bonded by a bond selected from the group consisting of sp ² bonds and sp ³ bonds, The ratio of the ^sp2 bonds in all bonds between carbon atoms is 1% or more and 25% or less, the extinction coefficient at a wavelength of 632.8 nm is 0.02 or more and 0.04 or less, and the hydrogen-containing The amount is 5 atomic % or less.

Further, in order to solve the above problems, a sliding member according to an aspect of the present invention is a sliding member that slides in the presence of oil, and has a sliding portion on the surface thereof. It has the above carbon film.

According to one aspect of the present invention, it is possible to provide a carbon film and a sliding member that are excellent in wear resistance and low friction in high-speed sliding at a sliding speed exceeding 1 m/s in oil.

One embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more and B or less".

[Carbon film]
A carbon film according to an aspect of the present invention is composed of carbon atoms bonded substantially by bonds selected from the group consisting of sp ² bonds and sp ³ bonds. A carbon film is usually an amorphous carbon film in which sp ² bonds and sp ³ bonds are mixed. Bonds possessed by carbon atoms in the carbon film are substantially only sp ² bonds and sp ³ bonds.

[ratio of ^sp2 binding]
In this embodiment, the ratio of sp ² bonds in all bonds of carbon atoms constituting the carbon film is 1% or more and 25% or less. If the proportion of sp ² bonds exceeds 25%, wear resistance may become insufficient, and low friction properties may become insufficient. From the viewpoint of sufficiently exhibiting both wear resistance and low friction properties, the ratio of ^sp2 bonds in the carbon film is preferably 20% or less, more preferably 15% or less.

On the other hand, there is no problem even if the ratio of ^sp2 bonds in the carbon film is low from the viewpoint of wear resistance and low friction. On the other hand, the lower limit of the ratio can be appropriately determined from the viewpoint of realizing a carbon film that can obtain the effects of the present embodiment, for example, manufacturing reasons such as the viewpoint of film formation conditions. From this point of view, the ratio of sp ² bonds in the carbon film may be 1% or more. The ratio of ^sp2 bonds in the carbon film is preferably 5% or more, more preferably 10% or more, from the viewpoint of relatively easy control of the production conditions and production of a carbon film with sufficient performance. preferable.

The ratio of ^sp2 bonds possessed by carbon atoms in the carbon film can be measured using a known method. In this embodiment, as described later in Examples, the measurement can be performed by electron energy loss spectroscopy (TEM-EELS) using a transmission electron microscope. In this embodiment, the integrated intensity is obtained from the integrated intensity at the energy specific to graphite and the integrated intensity at the energy specific to diamond.

The ratio of ^sp2 bonds in the carbon film can be adjusted by the manufacturing conditions of the carbon film. For example, the ratio of ^sp2 bonds in the carbon film tends to be higher when the arc current value in the manufacturing method described later is higher.

As described above, the carbon film of this embodiment consists essentially of sp ² bonds and sp ³ bonds. Therefore, the proportion of sp ² bonds in the carbon film can be rephrased in terms of sp ³ bonds. For example, the ratio of sp ³ bonds in all bonds possessed by the carbon atoms constituting the carbon film of the present embodiment may be any numerical value within the range of more than 75% and less than 99% for the reasons described above.

[Extinction coefficient]
The carbon film of this embodiment has an extinction coefficient of 0.02 or more and 0.04 or less at a wavelength of 632.8 nm. The extinction coefficient is the imaginary part k of the complex index of refraction, and is a value that indicates the attenuation of light in the carbon film. The smaller the extinction coefficient of the carbon film, the less likely it is to absorb light and the more transparent it tends to be. The extinction coefficient is correlated with the ratio of ^sp2 bonds in the carbon film, the content of elements other than carbon such as argon and hydrogen, and the density of defects (such as atomic vacancies). Extinction coefficient tends to be small. The extinction coefficient k, which is an optical constant, is a function of wavelength and takes different values depending on the wavelength. In the present invention, the value of the extinction coefficient at a wavelength of 632.8 nm is used as a representative value of the extinction coefficient of the carbon film of this embodiment. The extinction coefficients described below indicate the extinction coefficient of the carbon film at a wavelength of 632.8 nm, unless the wavelength is indicated. If the extinction coefficient is larger than 0.04, the wear resistance may become insufficient, and the low friction properties may become insufficient. From the viewpoint of sufficiently exhibiting both wear resistance and low friction properties, the extinction coefficient is preferably 0.035 or less, more preferably 0.03 or less.

On the other hand, from the viewpoint of wear resistance and low friction, the lower the extinction coefficient, the better. It can be determined as appropriate from manufacturing reasons such as film formation conditions. From this point of view, the carbon film may have an extinction coefficient of 0.02 or more. The extinction coefficient is preferably 0.025 or more from the viewpoint of relatively easy control of the production conditions and production of a carbon film with sufficient performance.

The extinction coefficient of the carbon film can be measured by known techniques. The extinction coefficient of a carbon film can be measured using, for example, an optical interference film thickness gauge or a spectroscopic ellipsometer.

The extinction coefficient of the carbon film can be adjusted by the manufacturing conditions of the carbon film. For example, the extinction coefficient tends to be higher when the current value of the arc discharge, the temperature of the substrate, or the supply amount of the inert gas in the manufacturing method described later is higher.

[Hydrogen content]
The hydrogen content of the carbon film of this embodiment is 5 atomic % or less. If the hydrogen content of the carbon film exceeds 5 atomic %, the number of bonds that are not used for bonding between carbon atoms in the carbon film increases, and sufficient mechanical properties such as hardness as a DLC film may not be exhibited. . From the viewpoint of sufficiently expressing the mechanical properties, the hydrogen content of the carbon film is preferably 3 atomic % or less, more preferably 2 atomic % or less.

From the viewpoint of the above mechanical properties, the hydrogen content of the carbon film is preferably as low as possible. It can be determined as appropriate. For example, the hydrogen content of the carbon film may be 1 atomic % or more from the viewpoint of relatively easily controlling the manufacturing conditions.

The hydrogen content of the carbon film can be determined by a known technique. For example, the hydrogen content of the carbon film of the present embodiment can be determined by RBS/ It can be measured by HFS analytical method.

In this embodiment, the hydrogen content of the carbon film can be adjusted by adjusting the manufacturing conditions of the carbon film. The hydrogen content of the carbon film of the present embodiment tends to increase, for example, when the initial degree of vacuum in the film-forming atmosphere in the manufacturing method described later is higher.

[hardness]
The hardness of the carbon film can be appropriately determined within the range in which the effects of the present embodiment can be obtained. If the hardness of the carbon film is too low, it may become impossible to use it for the intended purpose. From the viewpoint of being used for the sliding member that slides in the presence of oil, the hardness of the carbon film is preferably 40 GPa or more, more preferably 45 GPa or more, and even more preferably 50 GPa or more. .

Further, the hardness of the carbon film may be high from the viewpoint of expressing the desired mechanical properties, but it can be determined within a range that can be realized in the form of the film. For example, the hardness of the carbon film may be 80 GPa or less, 70 GPa or less, or 60 GPa or less from the viewpoint of relatively easy control of manufacturing conditions.

The hardness of the carbon film can be measured by a known method for measuring film hardness. For example, the hardness of a carbon film can be measured by nanoindentation, as described later in Examples.

The hardness of the carbon film can be adjusted by the manufacturing conditions of the carbon film. For example, the hardness of the carbon film tends to decrease as the temperature of the base material increases in the production of the carbon film.

[Thickness]
The film thickness of the carbon film can be appropriately determined within the range in which the effects of the present embodiment can be obtained. If the film thickness of the carbon film is too thin, the effects of the present embodiment, including the mechanical properties, may not be fully exhibited to the desired extent. If the film thickness of the carbon film is too thick, excessive internal stress is applied when it is formed on the sliding portion of the sliding member, which may cause breakage of the carbon film or malfunction of the sliding member.

From the viewpoint of sufficiently expressing the desired characteristics in the intended use, the film thickness of the carbon film is preferably 0.03 μm or more, more preferably 0.5 μm or more, and 1 μm or more. is more preferred. From the same viewpoint, the film thickness of the carbon film is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

The film thickness of the carbon film can be measured by a known method. Also, the film thickness of the carbon film can be adjusted by the manufacturing conditions of the carbon film. For example, the film thickness of the carbon film can be increased by lengthening the film formation time in manufacturing, which will be described later.

[Membrane structure]
The carbon film of this embodiment may have various forms as long as the effects of this embodiment can be obtained. For example, the carbon film of this embodiment may have a single-layer structure or a multi-layer structure. When the carbon film has a multi-layered structure, the carbon film as a whole should have the physical properties described above, and may include layers outside the numerical ranges described above. Moreover, as long as the carbon film as a whole has the physical properties described above, the physical properties may be uneven in the film thickness direction of the carbon film. For example, the hydrogen content may differ between one side and the other side of the carbon film.

[Method for producing carbon film]
The carbon membrane of this embodiment can be produced by a known method as described in Patent Document 1. For example, carbon films can be produced by depositing carbon atoms from a carbon source onto a substrate by cathodic arc discharge in a vacuum environment. Such a manufacturing method can be carried out using a vacuum arc vapor deposition apparatus (arc ion plating apparatus). A carbon electrode is preferably used as the carbon source.

The vacuum arc vapor deposition apparatus preferably has a magnetic filter from the viewpoint of suppressing adhesion of macroparticles (coarse particles) of the cathode material of about several μm to several tens of μm to the substrate.

In the manufacturing method, an inert gas such as argon gas and helium gas may be introduced from the viewpoint of stabilizing the arc discharge. The supply amount of the inert gas can be appropriately determined in the range of 0 to 5 sccm from the viewpoint of stabilizing the arc discharge and achieving the desired degree of vacuum in the film forming atmosphere.

From the viewpoint of preventing incorporation of inert gas elements into the film and obtaining a carbon film having the aforementioned extinction coefficient, the amount of inert gas introduced is preferably as small as possible. In addition, from the viewpoint of reducing the ratio of the ^sp2 component and obtaining a film with high hardness, it is preferable to introduce less inert gas.

The temperature of the substrate during film formation is usually determined according to the arc discharge current, and tends to increase as the current increases. Also, if the temperature of the substrate during film formation is too high, a carbon film having desired physical properties may not be produced. From the viewpoint of realizing the desired physical properties of the carbon film, the temperature of the substrate during film formation may be appropriately determined so as not to exceed 100°C. In addition, a cooling step may be performed to interrupt the film formation and lower the temperature of the substrate so that the temperature of the substrate does not exceed 100°C.

Similarly, the arc discharge current may be appropriately determined from the range of 30 to 80 A from the viewpoint of realizing the desired physical properties of the carbon film. If the current is large, it is necessary to lengthen the cooling process or repeat film formation and cooling in a short period of time in order to maintain the substrate temperature within the above temperature range. Also, the pressure of the film-forming atmosphere can be appropriately determined within a range in which vacuum vapor deposition of carbon by arc discharge can be realized, and may be appropriately determined within the range of 0.001 to 0.01 Pa, for example.

[Sliding member]
A sliding member according to one embodiment of the present invention is a sliding member that slides in the presence of oil, and has the carbon film of this embodiment on the sliding portion of the surface thereof. The sliding member can be composed of the carbon film of the present embodiment and a substrate carrying the carbon film on its surface.

The base material may be any member as long as it is used as a sliding member. The material and shape of the base material can be appropriately determined within the range of use as the sliding member. In addition, at least the portion of the substrate supporting the carbon film preferably has conductivity from the viewpoint of directly forming the carbon film. Examples of substrate materials include iron, cast iron, cemented carbide, chrome molybdenum steel, stainless steel and aluminum alloys.

In addition, the base material may be subjected to a treatment for increasing hardness, at least at the portion supporting the carbon film. For example, the base material may have a hard coating or a plated layer at least on the portion supporting the carbon film. Examples of hard coatings include metal nitride coatings, metal carbonitride coatings, and metal carbide coatings; examples of metal nitrides include chromium nitride and titanium nitride. Alternatively, when the base material is a ferrous material, the portion of the base material may be subjected to hardening treatment such as quenching and tempering, carburizing treatment, or nitriding treatment.

Further, the substrate may have an intermediate layer between the substrate and the carbon film for increasing interlayer adhesion strength from the viewpoint of supporting the carbon film more firmly. Examples of intermediate layer materials include one or more elements selected from the group consisting of Cr, Ti, Co, V, Mo and W, their carbides, nitrides and carbonitrides, and SiC. One or more ingredients selected from the group are included.

The intermediate layer can be formed on the surface of the substrate by known methods such as arc ion plating, sputtering and plasma CVD. The thickness of the intermediate layer can be appropriately determined within a range that exhibits sufficient adhesion to both the surface of the base material and the carbon film. You can decide.

The sliding member of this embodiment exhibits excellent slidability and durability as a member that slides at high speed in the presence of oil. The sliding member of the present embodiment is preferably a member used for applications that slide at high speed in the presence of oil, and examples of the sliding member include automobile parts and machine parts. Examples of automotive parts include cams, shims, valve lifters, plungers and piston rings. Examples of mechanical parts include shafts, bearings and gears.

The oil that intervenes when the sliding member is used is not limited, but is usually lubricating oil. The oil may be liquid or solid, and its composition is not limited. The oil can be appropriately determined according to the use of the sliding member. For example, if the sliding member is a component within an internal combustion engine, the oil is engine oil.

[Effect]
In the carbon film of the present embodiment, the ratio of ^sp2 bonds is 1% or more and 25% or less, the extinction coefficient at a wavelength of 632.8 nm is 0.02 or more and 0.04 or less, and the hydrogen content is 5 atomic %. It is below. As will be described later in Examples, the carbon film of the present embodiment exhibits excellent low friction and wear resistance, especially in high-speed sliding in the presence of oil, because of the physical properties described above.

In addition, the carbon film of the present embodiment has sufficiently high hardness and sufficient film thickness, so that it can be applied to various mechanical parts that slide during use.

By having such a carbon film on at least the sliding portion, it is possible to construct a sliding member suitable for the above-described mechanical component.

〔summary〕
The carbon film in the embodiment of the present invention is composed of carbon atoms bonded by bonds selected from the group consisting of sp ² bonds and sp ³ bonds. The ratio of ^sp2 bonds in all bonds of the carbon atoms constituting the carbon film is 1% or more and 25% or less, and the extinction coefficient at a wavelength of 632.8 nm is 0.02 or more and 0.04 or less. and the hydrogen content is 5 atomic % or less. Therefore, the embodiment of the present invention can provide a carbon film that is excellent in wear resistance and low friction in high-speed sliding at a sliding speed exceeding 1 m/s in oil.

In the carbon film of the embodiment of the present invention, the hydrogen content of 3 atomic % or less is more effective from the viewpoint of sufficiently expressing the mechanical properties of the carbon film.

In the carbon film of the embodiment of the present invention, a hardness of 40 GPa or more and 80 GPa or less is more effective from the viewpoint of sufficiently expressing the mechanical properties according to the intended use of the carbon film.

In the carbon film of the embodiment of the present invention, the film thickness of 0.03 μm or more and 50 μm or less is more effective from the viewpoint of applying the carbon film to the intended use.

The sliding member in the embodiment of the present invention is a sliding member that slides in the presence of oil, and has the carbon film on the sliding portion of its surface. Therefore, the embodiments of the present invention can provide carbon films and sliding members that are excellent in wear resistance and low friction.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

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

[Preparation of base material]
A substrate (disc-shaped, material SCM415, diameter: 32 mm, thickness: 3 mm) was prepared as the base material described above.

[Example 1]
The substrate was washed to remove stains such as rust preventive oil adhering to the substrate. The cleaned substrate was attached to a film forming jig, and the film forming jig was placed on one axis of a rotating/revolving turntable installed in a film forming chamber of a vacuum arc vapor deposition apparatus. After the chamber was evacuated to a pressure of 0.05 Pa, the substrate was heated at 180° C. for 30 minutes with a heater in the chamber. After that, heating by the heater was stopped, and the inside of the chamber was evacuated until the chamber pressure reached 0.002 Pa.

Argon gas was flowed into the chamber at 5 sccm, and a bias voltage of -700 V was applied to the substrate, and an arc current of 45 A was passed through the chromium cathode for 3 minutes to etch the surface of the substrate with chromium ions.

After evacuating the chamber to a pressure of 0.001 Pa or less, the discharge current of the arc discharge is set to 40 A, and the carbon film 1 is formed on the surface of the substrate while evaporating the carbon cathode (98 atomic % or more of carbon) by arc discharge. formed. The bias of the substrate during the production of the carbon film 1 was −50 V, and the film formation was interrupted halfway so that the temperature of the substrate did not exceed 100° C., and the film thickness was reduced to about 1 μm while repeating film formation and cooling. A carbon film was formed so as to

[Example 2]
A carbon film 2 was formed on the surface of the substrate in the same manner as in Example 1, except that the film formation and cooling were repeated so that the temperature of the substrate during the carbon film formation did not exceed 70°C.

[Example 3]
A carbon film 3 was formed on the surface of the substrate in the same manner as in Example 1, except that the film formation and cooling were repeated so that the temperature of the substrate during the carbon film formation did not exceed 55°C.

[Example 4]
A carbon film 4 was formed on the surface of the substrate in the same manner as in Example 1, except that argon gas was introduced into the chamber at a flow rate of 2 sccm during arc discharge during carbon film formation, and the substrate bias voltage was set to 0V.

[Comparative Example 1]
Carbon was deposited on the surface of the substrate in the same manner as in Example 1, except that argon gas was introduced into the chamber at a flow rate of 8 sccm during arc discharge during the formation of the carbon film, and the film was continuously formed without interruption for cooling the substrate. A film C1 was formed. The maximum temperature of the substrate during the production of the carbon film C1 was 178°C.

[Comparative Example 2]
The discharge current of the arc discharge during the carbon film formation was set to 80 A, argon gas was introduced into the chamber at a flow rate of 8 sccm during the arc discharge, the bias of the substrate was set to -150 V, and the substrate was cooled continuously without interruption. A carbon film C2 was formed on the surface of the substrate in the same manner as in Example 1 except that the film was formed. The maximum temperature of the substrate during the production of the carbon film C2 was 250.degree.

[Comparative Example 3]
A carbon film C3 was formed on the surface of the substrate in the same manner as in Example 1 except that the bias voltage of the substrate during the carbon film formation was set to 0 V and the film was formed continuously without interruption for cooling the substrate. The maximum temperature of the substrate during the production of the carbon film C3 was 150.degree.

〔evaluation〕
The following items were evaluated for the carbon films 1 to 4 and C1 to C3 obtained in Examples 1 to 4 and Comparative Examples 1 to 3.

(1) sp ² bond ratio The ratio of sp ² bonds to sp ³ bonds in carbon films was measured by electron energy loss spectroscopy (TEM-EELS) using a scanning transmission electron microscope.

More specifically, for the carbon film, electron energy loss spectrum data was obtained at an energy interval of 0.3 eV or less, and the integrated intensity (Sπ) of 284.1 to 285.6 eV and 292.8 to 294.3 eV The integrated intensity (Sσ) was determined.

Separately, electron energy loss spectrum data was similarly obtained for graphite and diamond. Then, the integrated intensity of graphite from 284.1 to 285.6 eV (Sgπ) and the integrated intensity from 292.8 to 294.3 eV (Sgσ) were obtained. Also, the integrated intensity (Sdπ) of 284.1 to 285.6 eV and the integrated intensity (Sdσ) of 292.8 to 294.3 eV of diamond were obtained.

From the integrated intensity obtained above, the ratio of sp ³ bonds in the carbon film was calculated from the following formula (1).
Ratio of sp ³ bonds [%]=[(Sgπ/Sgσ)−(Sπ/Sσ)]/[(Sgπ/Sgσ)−(Sdπ/Sdσ)]×100 (1)
Also, the ratio of sp ² bonds in the carbon film was calculated from the following formula (2).
Proportion of sp ² bonds [%] = 100-ratio of sp ³ bonds [%] (2)
(2) Extinction Coefficient of Carbon Film For measuring the extinction coefficient of the carbon film, an optical interferometric thickness gauge manufactured by FILMETRICS Co., Ltd. was used. Cauchy is used as the model of the optical constants of the carbon film, the measurement type is reflectance measurement, the incident angle is 0 degrees, and the polarization is TE. An extinction coefficient at a wavelength of 632.8 nm was obtained.

(3) Hydrogen content of carbon film The RBS/HFS analysis method was applied to the carbon film formed on the smooth surface of the substrate to measure the hydrogen content of the carbon film. The hydrogen content of the carbon film was calculated by calculating the average value of the measured values at three points from the carbon film formed on the same smooth surface of the substrate.

(4) Hardness of Carbon Film The hardness of the carbon film was measured using a nanoindenter ENT1100a manufactured by Elionix Co., Ltd. under the conditions of a load of 300 mgf (2.94 mN), a load division number of 500 steps, and a load application time of 1 second.

(5) Friction coefficient and wear depth Using a substrate having a carbon film, a friction wear test was performed under the following test conditions, and the carbon film on the substrate was slid under low speed (10 rpm) and The friction coefficient and wear depth of the carbon film under high-speed sliding (600 rpm) were measured. Table 2 shows the friction coefficient and wear depth at 600 rpm. The coefficient of friction is the average value during the 60 minute test. The moving speed of the substrate in the low-speed sliding is 21 mm/sec, and the moving speed of the substrate in the high-speed sliding is 1257 mm/sec. If the coefficient of friction at 600 rpm is 0.030 or less, it can be judged to have excellent low friction properties in high-speed sliding in the presence of engine oil.

(Test condition)
Test equipment: Block-on-ring type rotary sliding test equipment (ring rotates in one direction)
Ring: Material FCD600 (JIS G 5502 compliant spheroidal graphite cast iron), outer diameter 40 mm, inner diameter 30 mm, width 20 mm
Rotation speed: 10rpm and 600rpm
Test time: 60 minutes Test temperature: 40-50°C
Surface pressure: 0.23 MPa
Lubricating oil: Lubricating oil (0W-20, containing MoDTC) is dropped on the surface of the carbon film on the substrate at a rate of 1 drop per 5 seconds. The needle of the stylus type surface roughness meter is scanned from the non-sliding part to the sliding part and again to the non-sliding part so as to vertically cross the sliding mark with a ring width of 20 mm formed on the surface of the non-sliding surface. The step between the moving part and the sliding part was measured. The measurement was performed at three points for one sliding mark, and the average value of the steps was taken as the wear depth of the carbon film. If the wear depth is 0.04 μm or less, it can be judged to have excellent wear resistance in high-speed sliding in the presence of engine oil.

Table 1 shows the manufacturing conditions of carbon films 1 to 4 and C1 to C3. Table 2 shows the physical properties of carbon films 1 to 4 and C1 to C3, and the results of high-speed friction and wear tests. Furthermore, Table 3 shows the friction coefficients of carbon film 1 and carbon film C1 under low-speed sliding and high-speed sliding.

[Discussion]
As is clear from Table 1, all of carbon films 1 to 4 have excellent low friction properties and wear resistance in high-speed sliding in the presence of engine oil.

Among them, the carbon film 3 is superior in both low wear and wear resistance. It is considered that this is because the sp2 binding ratio is small and the extinction coefficient is low.

Furthermore, as is clear from Table 3, carbon film 1 and carbon film C1 exhibit substantially the same coefficient of friction in low-speed sliding, but the friction coefficient of carbon film 1 in high-speed sliding is Clearly lower than that of C1. Therefore, it can be seen that the carbon film 1 is superior to the conventional carbon film in low-friction properties particularly in high-speed sliding.

On the other hand, the carbon films C1 and C3 had good wear resistance, but insufficient low friction properties. This is probably because the ratio of sp ² bonds and the extinction coefficient of the carbon film C1 are both too high. This is probably because the carbon film C3 has a low extinction coefficient but a high ratio of sp ² bonds. From these results, it is believed that both the ratio of sp ² bonds and the extinction coefficient need to satisfy the low values within the range of the present invention in order to exhibit good low-friction properties.

Moreover, the carbon film C2 was insufficient in both low friction properties and wear resistance. This is probably because both the ratio of sp ² bonds in the carbon film and the extinction coefficient in the carbon film C2 were too high, and the film hardness was too low.

INDUSTRIAL APPLICABILITY The present invention is suitable for parts that require high low friction and high durability in high-speed sliding in the presence of oil, and can contribute to further expansion and development of technical fields using such parts. Be expected.

Claims (5)

A carbon film composed of carbon atoms bonded by a bond selected from the group consisting of sp ² bonds and sp ³ bonds,
The ratio of the sp ² bonds in all the bonds of the carbon atoms constituting the carbon film is 1% or more and 25% or less,
An extinction coefficient at a wavelength of 632.8 nm is 0.02 or more and 0.04 or less,
A carbon film having a hydrogen content of 5 atomic % or less. 2. The carbon film according to claim 1, wherein the hydrogen content is 3 atomic % or less. 3. The carbon film according to claim 1, which has a hardness of 40 GPa or more and 80 GPa or less. The carbon film according to any one of claims 1 to 3, wherein the film thickness is 0.03 µm or more and 50 µm or less. A sliding member that slides in the presence of oil, the sliding member having the carbon film according to any one of claims 1 to 4 on the sliding portion of its surface.