JP2021110403A - Slide member and piston ring - Google Patents

Abstract

To provide a slide member which can materialize all of excellent heat resistance, low aggression to a mating material, high wear resistance, and a low friction coefficient.SOLUTION: A slide member 100 has a base material 10 and an amorphous carbon film 20 formed on the base material 10, and having a surface 20A being a slide surface. The amorphous carbon film 20 has a component composition containing a hydrogen content in an amount of 3 atom% or less and the remainder composed of carbon, and has a thickness of 3 μm or more. The arithmetic average roughness of the surface 20A of the amorphous carbon film is 0.10 μm or less. A hard region 18A with an indentation hardness of 25 GPa or more, and a soft region 18B with an indentation hardness of 20 GPa or less are mixedly formed on the surface 20A of the amorphous carbon film, and when an area of the hard region 18A on the surface 20A is denoted as A, and an area of the soft region 18B is denoted as B, A/(A+B) is 0.20 or more, and 0.70 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to sliding members, particularly sliding members that require high reliability, such as automobile parts such as piston rings.

In recent years, in internal combustion engines centered on automobile engines, higher output, longer life, and improved fuel efficiency have been required. Therefore, for example, it is generally practiced to form a hard carbon film known to have a low friction coefficient on the sliding surface of a sliding member used in an internal combustion engine or the like.

Examples of this hard carbon film include amorphous carbon called diamond-like carbon (DLC). The structural essence of DLC is a mixture ^{of diamond bonds (sp 3} bonds) and graphite bonds (sp ^{2 bonds) as carbon bonds.} Therefore, DLC has hardness, abrasion resistance, thermal conductivity, and chemical stability similar to diamond, while having solid lubricity similar to graphite, and is therefore suitable as a protective film for, for example, automobile parts. be.

The DLC film has different characteristics that can be advantageously exhibited depending on its hardness. In general, a hard DLC film has a ^{low sp 2} ratio, so that it is difficult to obtain a low friction coefficient, but it is excellent in wear resistance. On the other hand, the soft DLC film has a ^{high sp 2} ratio and a low friction coefficient can be obtained, but the wear resistance is not as good as that of the hard DLC film.

Therefore, a sliding member that combines a hard DLC film and a soft DLC film has been proposed. In Patent Document 1, a DLC film is formed on the outer peripheral surface of the piston ring, and this DLC film is a laminated film in which two or more layers having different hardness are laminated, and the hardness of the two layers is high. It is stated that the difference is 500 to 1700 HV, the high hardness layer has a thickness equal to or greater than the thickness of the low hardness layer, and the total thickness of the DLC film is 5.0 μm or more. ..

Japanese Unexamined Patent Publication No. 2012-202522

Patent Document 1 describes that the outermost layer of the DLC film made of a laminated film is a layer having high hardness. However, according to the study of the present inventor, the following has been found. That is, if the outermost layer of the DLC film is a layer with high hardness, the sp ² ratio of the surface of the DLC film is low at the initial stage of sliding, so even if the layer with low hardness is exposed during the sliding process, friction is performed. A low coefficient of friction could not be obtained in the early stages of motion. On the other hand, when the outermost layer of the DLC film is a layer having a low hardness, there is a problem that the heat resistance of the DLC film is insufficient, the wear resistance is low, and the aggression to the mating material is high. rice field.

Therefore, in view of the above problems, it is an object of the present invention to provide a sliding member capable of achieving all of excellent heat resistance, low aggression against a mating material, high wear resistance, and low friction coefficient. do.

As a result of diligent studies by the present inventor in order to solve the above problems, a hard region and a soft region are formed on the surface of the amorphous carbon film (DLC film) before sliding, that is, when the sliding member is not used. By setting the area ratio of the hard region and the soft region on the surface to a predetermined range, excellent heat resistance, low aggression against the mating material, high wear resistance, and low friction coefficient It was found that all the characteristics of the above can be realized.

The abstract structure of the present invention completed based on the above findings is as follows.
(1) Base material and
An amorphous carbon film having a hydrogen content of 3 atomic% or less and a component composition in which the balance is composed of carbon and having a thickness of 3 μm or more, which is formed on the base material and whose surface is a sliding surface.
Have,
The surface of the amorphous carbon film has an arithmetic mean roughness Ra of 0.10 μm or less.
On the surface of the amorphous carbon film, a hard region having an indentation hardness of 25 GPa or more and a soft region having an indentation hardness of 20 GPa or less are mixed.
A sliding member having an A / (A + B) of 0.20 or more and 0.70 or less, where A is an area of a hard region and B is an area of a soft region on the surface.

(2) In the amorphous carbon film,
In the portion of the hard region of the surface, only the hard portion exists in the depth direction from the surface.
The sliding member according to (1) above, wherein in the portion of the soft region of the surface, the soft portion is first located in the depth direction from the surface, and then the hard portion is located.

(3) One or more elements selected from the group consisting of Cr, Ti, Co, V, Mo, Si and W, or carbides and nitrides thereof, between the base material and the amorphous carbon film. The sliding member according to (1) or (2) above, which has an intermediate layer made of carbide.

(4) A piston ring made of the sliding member according to any one of (1) to (3) above, wherein the outer peripheral surface thereof is the sliding surface.

The sliding member of the present invention can realize all of excellent heat resistance, low aggression against the mating material, high wear resistance, and low friction coefficient.

It is a schematic cross-sectional view of the sliding member 100 by one Embodiment of this invention. It is a figure which schematically explains a part of the manufacturing process of the sliding member 100 by one Embodiment of this invention. It is sectional drawing of the piston ring 200 by one Embodiment of this invention.

(Sliding member)
With reference to FIG. 1, the sliding member 100 according to the embodiment of the present invention is used under lubricating oil, and is formed on the base material 10 and the base material 10, and the surface 20A slides on the base material 10. It has an amorphous carbon film (DLC film) 20 as a surface. Further, optionally, an intermediate layer 12 may be provided between the base material 10 and the amorphous carbon film 20.

[Base material]
The material of the base material 10 is not particularly limited as long as it has the strength required as the base material of the sliding member. When the sliding member 100 of the present embodiment is a piston ring, preferred materials for the base material 10 include steel, martensitic stainless steel, austenitic stainless steel, and high-grade cast iron. When the sliding member 100 of the present embodiment is a seal ring such as a CVT, resin is mentioned as the material of the base material 10, and when it is used as a vane of a compressor or the like, aluminum alloy or the like is mentioned as the material of the base material 10. Be done.

The roughness of the surface of the base material 10 (the surface on which the DLC film is formed) is preferably 0.01 μm or more in arithmetic average roughness Ra. When the surface roughness of the base material 10 is less than 0.01 μm in Ra, the surface becomes almost a mirror surface, and the hard DLC layer 14 (see FIGS. 1 and 2) having an appropriate surface roughness described later cannot be formed. Is. The upper limit of the surface roughness of the base material 10 is not particularly limited, but from the viewpoint of facilitating the formation of the DLC film 20, the surface roughness of the base material 10 is preferably 1.3 μm or less in Ra. The surface roughness of the base material 10 can be controlled by adjusting the degree of polishing of the base material surface. Further, the surface of the base material can be honed to intentionally form the surface roughness.

"Ra on the surface of the base material" shall be measured by the following method. That is, at an arbitrary position on the surface of the base material, according to JIS B0601 (2001), the base material has a reference length of 1.25 mm, a cutoff value of λc: 0.25 mm, and a cutoff ratio of λc / λs = 100. The roughness curve is measured to obtain the arithmetic mean roughness Ra. The measurement shall be performed three times, and the average value of the three times shall be adopted.

[Middle class]
The intermediate layer 12 has a function of relaxing the stress at the interface with the base material 10 and enhancing the adhesion of the DLC film 20 by being formed between the base material 10 and the DLC film 20. From the viewpoint of demonstrating this function, the intermediate layer 12 is composed of one or more elements selected from the group consisting of Cr, Ti, Co, V, Mo, Si and W or their carbides, nitrides and carbonitrides. It is preferable to use the above. From the viewpoint of sufficiently enhancing the adhesion of the DLC film 20, the thickness of the intermediate layer 12 is preferably 0.1 μm or more, and more preferably 0.2 μm or more. Further, from the viewpoint of sufficiently suppressing the intermediate layer 12 from causing plastic flow during sliding and peeling off the DLC film 20, the thickness of the intermediate layer 12 is preferably 0.6 μm or less, preferably 0.5 μm. It is more preferable that it is as follows.

As a method for forming the intermediate layer 12, for example, a sputtering method can be mentioned. The washed base material 10 is placed in the vacuum chamber of the PVD film forming apparatus, and the intermediate layer 12 is formed by sputter discharge of the target with Ar gas introduced. The target may be selected from Cr, Ti, Co, V, Mo, Si and W. The thickness of the intermediate layer 12 can be adjusted by adjusting the discharge time of the target.

[DLC film]
<Component composition of DLC film>
The DLC film 20 has a component composition in which the hydrogen content is 3 atomic% or less and the balance is carbon. The amorphous carbon can be confirmed by Raman spectrum measurement using a Raman spectrophotometer (Ar laser).

When the DLC film contains hydrogen, when the temperature of the DLC film becomes high due to sliding, the hydrogen is desorbed and the DLC film is deteriorated, so that the wear of the DLC film is promoted. Therefore, in the present embodiment, it is assumed that the DLC film 20 does not substantially contain hydrogen, that is, the hydrogen content is 3 atomic% or less. This makes it possible to avoid deterioration of wear resistance due to the release of hydrogen in a high temperature environment.

<Measurement method of hydrogen content of DLC film>
The hydrogen content of the DLC film is evaluated by RBS (Rutherford Backscattering Spectrometry) / HFS (Hydrogen Forward Scattering Spectroscopy) for the DLC film formed on a flat surface or a surface having a sufficiently large curvature. be able to. On the other hand, the DLC film formed on an uneven sliding surface such as the outer peripheral surface of the piston ring is evaluated by combining RBS / HFS and SIMS (Secondary Ion Mass Spectrometry). Although RBS / HFS is a known method for analyzing a film composition, it cannot be applied to the analysis of uneven surfaces. Therefore, RBS / HFS and SIMS are combined as follows.

First, as a reference sample having a flat surface, a mirror-polished flat test piece (hardened SKH51 disk, φ25 × thickness 5 mm, hardness HRC60 to 63) is subjected to carbon to be measured as a reference value. Form a film.

The film is formed on the reference sample by introducing _{C 2} H ₂ , Ar, and H _{2 as atmospheric gases using a reactive sputtering method.} Then, by varying the flow rate of H ₂ and / or C ₂ H ₂ flow rate is introduced to adjust the amount of hydrogen contained in the carbon film. In this way, carbon films composed of hydrogen and carbon and having different hydrogen contents are formed, and the hydrogen content and carbon content of these are evaluated by RBS / HFS.

Next, the above sample is analyzed by SIMS to measure the secondary ionic strength of hydrogen and carbon. Here, SIMS analysis can also measure a film formed on an uneven surface, for example, the outer peripheral surface of a piston ring. Therefore, for the same film of the reference sample with the carbon film, the hydrogen content and carbon content (unit: atomic%) obtained by RBS / HFS and the secondary ions of hydrogen and carbon obtained by SIMS. Obtain an empirical formula (calibration curve) showing the relationship with the strength ratio. By doing so, the hydrogen content and the carbon content can be calculated from the secondary ionic strengths of hydrogen and carbon of SIMS measured on the outer peripheral surface of the actual piston ring. As the value of the secondary ionic strength by SIMS, the average value of the secondary ionic strength of each element observed at least at a depth of 20 nm or more from the surface of the carbon film and in the range of 50 nm square is adopted.

<Thickness of DLC film>
In the present embodiment, the thickness of the DLC film 20 is 3 μm or more. This is because when the thickness is less than 3 μm, the effect of the present invention expected by the DLC film 20 is not sufficiently exhibited. The upper limit of the thickness of the DLC film is not particularly limited, but the thickness of the DLC film 20 is preferably 40 μm or less from the viewpoint of ensuring adhesion to the substrate and preventing peeling. In the present invention, the thickness of the DLC film is determined by observing a resin-embedded sample including a cross section along the thickness direction of the DLC film, and in the cross section, from the recess of the base material or the intermediate layer to the surface of the DLC film. It shall be obtained by measuring the length.

<Surface morphology of DLC film>
With reference to FIGS. 1 and 2, in the present embodiment, the hard region 18A and the soft region 18B are formed on the surface 20A of the DLC film 20 before sliding, that is, when the sliding member 100 is not used. Keep mixed. Further, it is important that A / (A + B) is 0.20 or more and 0.70 or less, where A is the area of the hard region and B is the area of the soft region on the surface 20A.

The “hard region” means a DLC region having an indentation hardness of 25 GPa or more, and the indentation hardness of the hard region is preferably 30 GPa or more. The upper limit of the indentation hardness of the hard region is not particularly limited, but from the viewpoint of post-workability of the DLC film, the indentation hardness of the hard region is preferably 60 GPa or less.

The “soft region” means a DLC region having an indentation hardness of 20 GPa or less, and the indentation hardness of the soft region is preferably 15 GPa or less. The lower limit of the indentation hardness of the soft region is not particularly limited, but from the viewpoint of heat resistance, the indentation hardness of the soft region is preferably 5 GPa or more.

When A / (A + B) is less than 0.20, the hard region 18A is too small and the soft region 18B is too large on the surface 20A of the DLC film. In this case, there are the following three disadvantages. First, since the soft region 18B tends to be inferior in heat resistance to the hard region 18A, the heat resistance of the DLC film 20 becomes insufficient. Secondly, since the soft region 18B tends to be inferior in wear resistance to the hard region 18A, the wear resistance of the DLC film 20 becomes insufficient. Thirdly, the aggression to the partner material is increased. This is considered to be due to the following mechanism. With reference to FIG. 2, when the soft region 18B is excessive on the surface 20A of the DLC film, the hard DLC layer 14 is present inside the DLC film 20 while maintaining the surface roughness. Then, in the process of sliding, a large number of convex portions of the hard DLC layer 14 come into contact with the mating material, and as a result, the aggression to the mating material becomes high.

On the other hand, when A / (A + B) is 0.20 or more, the hard region 18A having excellent heat resistance and wear resistance is sufficiently present, so that the heat resistance and wear resistance of the DLC film 20 can be ensured. can. It is also possible to reduce the aggression to the partner material. This is because if the hard DLC layer 14 is exposed to some extent on the surface 20A of the DLC film and forms the hard region 18A at the stage before sliding, the convex portion of the hard DLC layer 14 will be formed with reference to FIG. This is because it has been removed to form a flat surface. That is, even if the exposure ratio of the hard DLC layer 14 increases in the sliding process, the protrusion does not attack the mating material. Therefore, A / (A + B) is set to 0.20 or more, preferably 0.25 or more.

When A / (A + B) exceeds 0.70, the hard region 18A is excessive and the soft region 18B is excessive on the surface 20A of the DLC film. In this case, since the ^{soft region 18B having a high sp 2} ratio and contributing to low friction is hardly exposed on the surface 20A of the DLC film at the initial stage of sliding, the friction coefficient becomes high at the initial stage of sliding. ..

On the other hand, when A / (A + B) is 0.70 or less, the soft region 18B is exposed to some extent on the surface 20A of the DLC film at the initial stage of sliding, so that the friction coefficient is low at the initial stage of sliding. Can be obtained. In the process of sliding, a ^{large amount of the hard DLC layer 14 which has a low sp 2} ratio and is disadvantageous for low friction is exposed. However, since the sliding is progressing, the surface of the hard DLC layer is exposed by frictional heat. The low coefficient of friction is maintained because the ^{sp 3} component is continuously ^{changed to the sp 2 component.} Therefore, A / (A + B) is set to 0.70 or less, preferably 0.65 or less.

In addition, A / (A + B) shall be obtained by the following method. The ratio ID / IG of the peak intensity of the D band to the peak intensity of the G band in the Raman spectroscopic spectrum obtained by measuring the DLC film by Raman spectroscopy correlates with the hardness of the DLC film. / IG becomes low. Therefore, it is possible to determine whether the measurement point is a hard region or a soft region from the ID / IG value obtained at a certain measurement point. Specifically, ID / IG separates the Raman spectroscopic spectrum into a D band ^{having a peak near 1350 cm -1} and a G band having a peak near ^{1550 cm -1 by curve fitting by a Gaussian function.} It is obtained by determining the ratio of the peak intensity of the D band to the peak intensity. The ID / IG used in the present invention is a ratio of peak intensities. Specifically, three measurement regions of 25 mm × 25 mm are set at arbitrary positions on the surface of the DLC film, and ID / IG in the measurement region is measured using an inViaReflex Raman spectrophotometer manufactured by Renishaw Co., Ltd. do. The measurement conditions are an Ar ion-excited laser wavelength: 532.0 nm, a laser output: 50 mW, an objective lens: 100 times, and a dimmer. Of all the measurement points in each measurement region, V1 was determined as the hard region and V2 was determined as the soft region, and V1 / (V1 + V2) was obtained in each measurement region. The three values are countably averaged to obtain A / (A + B).

The fact that the hard region 18A and the soft region 18B are "mixed" on the surface 20A of the DLC film means that the hard region 18A and the soft region 18B are dispersed and exist on the surface 20A of the DLC film.

<Method of forming DLC film>
A method of forming the DLC film 20 will be described with reference to FIGS. 1 and 2. The DLC film 20 can be formed, for example, by using a PVD method such as ion plating by vacuum arc discharge (VA method) using a carbon target. The PVD method can form a DLC film having high hardness and excellent wear resistance containing almost no hydrogen. When a DLC film is formed using the ion plating method by vacuum arc discharge, the hardness is (i) the discharge amount of the cathode, (ii) the arc current value, and (iii) the bias voltage applied to the substrate. Can be adjusted by. The higher the index, the lower the hardness of the DLC film. Further, the film thickness of the DLC film can be adjusted by changing conditions such as the discharge time of the target. The filter type cathode vacuum arc method (FCVA method) may be used.

First, a base material 10 having a surface roughness of Ra of 0.01 μm or more is prepared, and an intermediate layer 12 is optionally formed on the surface. After that, the hard DLC layer 14 is formed on the surface of the base material 10 or the surface of the intermediate layer 12 under the first condition in which the above (i) to (iii) are set to predetermined values. The surface of the hard DLC layer 14 is provided with a predetermined surface roughness due to the fact that the surface of the base material 10 is provided with a predetermined surface roughness and that dust and the like are taken into the film in the process of film formation. Be done.

Here, the surface roughness of the hard DLC layer 14 is preferably 0.1 μm or more and 0.8 μm or less in terms of arithmetic average roughness Ra. This is because by controlling the surface roughness within this range, it becomes easier to achieve the desired A / (A + B) as a result of the polishing process described later. The "Ra on the surface of the hard DLC layer" shall be measured by the following method. That is, at an arbitrary position on the surface of the hard DLC layer, according to JIS B0601 (2001), the hard DLC is under the conditions of a reference length: 1.25 mm, a cutoff value of λc: 0.25 mm, and a cutoff ratio of λc / λs = 100. The roughness curve of the layer is measured to obtain the arithmetic mean roughness Ra. The measurement shall be performed three times, and the average value of the three times shall be adopted.

The thickness of the hard DLC layer 14 may be appropriately determined in consideration of the target thickness of the DLC film 20, and may be substantially equal to the target thickness of the DLC film 20.

Next, the soft DLC layer 16 is formed on the surface of the hard DLC layer 14 under the second condition in which the above (i) to (iii) are changed. The surface roughness of the soft DLC layer 16 inherits the surface roughness of the hard DLC layer 14 to almost the same extent. The thickness of the soft DLC layer 14 is not particularly limited, but is preferably 0.1 μm or more and 5.0 μm or less. If it is less than 0.1 μm, it may be difficult to adjust the polishing amount described later, and if it exceeds 5.0 μm, the polishing amount required to achieve the desired A / (A + B) increases, resulting in cost and cost. It is not preferable from the viewpoint of productivity.

Next, the surface of the soft DLC layer 14 is polished to form the DLC film 20. By adjusting the polishing amount at that time, A / (A + B) is controlled in the range of 0.20 or more and 0.70 or less. That is, as the amount of polishing increases, the exposed portion (hard region 18A) of the hard DLC layer increases, so that A / (A + B) becomes large.

In such a method, the hard region 18A and the soft region 18B can be mixed on the surface 20A of the DLC film 20.

<Surface roughness of DLC film>
As a result of the polishing as described above, the surface roughness of the DLC film 20 becomes 0.10 μm or less in arithmetic average roughness Ra. The "Ra of the DLC film" shall be measured by the following method. That is, at an arbitrary position of the DLC film, according to JIS B0601 (2001), the rough DLC film is provided under the conditions of a reference length: 1.25 mm, a cutoff value of λc: 0.25 mm, and a cutoff ratio of λc / λs = 100. The radius curve is measured to obtain the arithmetic mean roughness Ra. The measurement shall be performed three times, and the average value of the three times shall be adopted.

<Morphology of DLC film in the thickness direction>
As shown in FIGS. 1 and 2, in the DLC film 20, only the hard portion (hard DLC layer 14) is present in the portion of the hard region 18A of the surface 20A in the depth direction from the surface, and the surface 20A is soft. In the region 18B, the soft portion (remaining portion of the soft DLC layer 14) is first located in the depth direction from the surface, and then the hard portion (hard DLC layer 14) is located. With this configuration, excellent heat resistance, low aggression against the mating material, high wear resistance, and low friction coefficient can all be realized.

(Manufacturing method of sliding member)
The method for manufacturing the sliding member 100 according to the embodiment of the present invention is as follows.
The process of preparing the base material 10 and
Optionally, a step of forming the intermediate layer 12 on the surface of the base material 10 and
A step of forming a hard DLC layer 14 having a predetermined surface roughness on the surface of the base material 10 or the surface of the intermediate layer 12.
The step of forming the soft DLC layer 16 on the hard DLC layer 14 and
A step of polishing the soft DLC layer 16 to form a DLC film 20 and
The hard region 18A where the hard DLC layer 14 is exposed and the soft region 18B where the soft DLC layer 16 remains are mixed on the surface 20A of the DLC film 20 by adjusting the polishing amount thereof, and the surface is It is characterized in that A / (A + B) is controlled to 0.20 or more and 0.70 or less, where A is the area of the hard region 18A and B is the area of the soft region 18B in 20A.

The sliding member 100 according to the embodiment of the present invention includes a piston ring, a piston, a piston pin, a tappet, a valve lifter, a shim, a rocker arm, and a cam used for a sliding portion of an internal combustion engine in which lubricating oil such as engine oil is interposed. , Camshafts, timing gears, timing chains, etc., vanes, injectors, plungers, cylinders, etc. used in fuel supply systems, etc. can be applied to various products.

(piston ring)
With reference to FIG. 3, the piston ring 200 according to the embodiment of the present invention has a ring shape with four surfaces of an outer peripheral surface 22, an inner peripheral surface 24, and upper and lower surfaces 26A and 26B, and the outer peripheral surface 22 is shown in FIG. It is formed by the DLC film 20 shown. That is, the piston ring 200 of the present embodiment is made of the sliding member 100, and the outer peripheral surface 22 thereof is the surface 20A of the DLC film shown in FIG. As a result, excellent heat resistance can be obtained on the outer peripheral surface 22 which is the sliding surface, the aggression against the inner peripheral surface of the cylinder which is the mating material is low, and further high wear resistance and low friction coefficient are realized. It is possible.

A Cr layer with a thickness of about 3 μm is provided as an intermediate layer on the outer peripheral surface (surface roughness Ra: 0.1 μm) of a silicon chrome steel piston ring having dimensions of a nominal diameter of 80 mm, a thickness of 2.5 mm, and a width of 1.2 mm. Formed. Then, DLC films of various levels shown in Table 1 were formed on the intermediate layer to obtain a sliding member. The DLC film was formed by the following procedure. First, using a film forming apparatus by a vacuum arc method, various conditions of arc current value and bias voltage are set using graphite as a cathode, and the surface of the intermediate layer has the "hard region hardness" shown in Table 1. A hard DLC layer was formed. At this time, the surface roughness Ra of the hard DLC layer was in the range of 0.2 to 0.5 μm at all levels. Subsequently, a soft DLC layer having the "soft region hardness" shown in Table 1 was formed on the surface of the hard DLC layer under the condition that the arc current value and the bias voltage were changed to high. Then, the soft DLC layer was polished to obtain a DLC film. At that time, by adjusting the polishing amount of the soft DLC layer, the value of A / (A + B) was controlled when the area of the hard region on the surface of the DLC film was A and the area of the soft region was B. However, the level No. In No. 1, only the soft DLC layer was formed, and the level No. In No. 11, only the hard DLC layer was formed. Table 1 shows the hydrogen content, thickness, surface Ra, indentation hardness of the hard region, indentation hardness of the soft region, and A / (A + B) of the DLC film. The indentation hardness was measured using an ultrafine indentation hardness tester manufactured by Elionix Inc. As a condition, the test was carried out using a Belkovic indenter under a load such that the indentation depth was about 1/10 of the thickness of the DLC film. In the measurement area of 1.0 mm × 1.0 mm, the load-unload hardness test was performed at multiple points of 100 × 100 points at 10 μm intervals, and the load-unload curve was judged to exclude abnormal values. Two levels of numbers are detected. Among them, the one with low hardness is defined as the hardness in the soft region, and the one with high hardness is defined as the hardness in the hard region. The hydrogen content, thickness, surface Ra, and A / (A + B) of the DLC film were measured by the methods described above.

The level No. of A / (A + B) = 0.00. In No. 2, the hard DLC layer is not exposed on the surface of the DLC film, the entire surface is composed of the soft DLC layer, and the hard DLC layer exists below the soft DLC layer. Level No. of A / (A + B) = 1.00. In 11, the DLC film consists only of a hard DLC layer. Other levels No. In 3 to 10, hard regions and soft regions are mixed on the surface of the DLC film, and in the hard region portion, only the hard region exists in the depth direction from the surface, and in the soft region portion, from the surface. The film form is such that the soft part is first located in the depth direction of the, and then the hard part is located.

[Evaluation of heat resistance]
The test pieces obtained by cutting from the piston rings of each level were put into an electric furnace and heat-treated at an atmospheric temperature of 250 ° C. for 100 hours. Then, the surface of the DLC film of the test piece was observed with an optical microscope. At that time, the level at which partial peeling, shedding, or disappearance was observed in the DLC film was marked with "x", and the level at which no peeling, shedding, or disappearing was observed was marked with "〇". The results are shown in Table 1.

[Evaluation of wear resistance and friction coefficient]
A rolling slip fatigue test was conducted under the following test conditions using test pieces obtained by cutting from piston rings of each level. In this test, a load is repeatedly applied to a test piece that slides with a rotating drum, and the wear resistance of the DLC film is evaluated from the amount of wear of the test piece.
Load: 20-50N, sine curve 50Hz
Mating material (drum): SUJ2 material with a diameter of 80 mm Sliding speed: Forward / reverse rotation pattern operation (± 10 m / s), holding for 20 seconds at a speed of ± 10 m / s Acceleration: 0.23 m / s ²
Lubricating oil: Additive-free motor oil, 0.1cc / min
Drum surface temperature: 80 ° C
Test time: After 10 cycles of 10 cycles with forward / reverse pattern operation as one cycle, the wear amount of the test piece is measured with a contact type shape measuring machine, and the wear amount is "◎" when the wear amount is 1.0 μm or less, and the wear amount is 1. The level of more than 0.0 μm and less than 2.0 μm was designated as “◯”, and the level of wear amount exceeding 2.0 μm was designated as “x”. Further, the friction coefficient up to 5 cycles was measured, and the level where the friction coefficient was 0.16 or less was set as "◯" and the level where the friction coefficient exceeded 0.16 was set as "x". The results are shown in Table 1.

[Evaluation of aggression against partner material]
Prepare a SUJ2 material (JIS G 4805) disc (φ25 mm x t8 mm) as the sliding partner material, and perform the following test conditions for the sliding members of each level by vibration friction wear test (Optimor: SRV tester). A reciprocating motion test was conducted at. After the test, the amount of wear of the mating material is measured, and the level of wear of 1.0 μm or less is “◎”, the level of wear of more than 1.0 μm and less than 2.0 μm is “○”, and the amount of wear is 2.0 μm. The level exceeding is set as "x". The results are shown in Table 1.
Test time: 10 min
Load: 100N
Reciprocating frequency: 50Hz
Amplitude: 3.0 mm
Lubricating oil: Engine oil 5W-30 (ester)
Lubricating oil temperature: 80 ° C

As is clear from Table 1, Comparative Example No. in which A / (A + B) is less than 0.20. In Nos. 1 to 3, the hard region was too small and the soft region was too large, so that they were inferior in terms of heat resistance and wear resistance. Among these comparative examples, No. 2 and No. In No. 3, the hard DLC layer existing inside the DLC film while maintaining the surface roughness is exposed in the process of sliding and comes into contact with the mating material, so that the aggression to the mating material is increased. Further, Comparative Example No. in which A / (A + B) exceeds 0.70. 10 and No. In No. 11, the soft region was too small and the hard region was too large, so that it was inferior in terms of friction coefficient. Of these comparative examples, No. In No. 11, since the hard DLC layer having a surface Ra of more than 0.10 μm comes into contact with the mating material from the initial stage of sliding, the aggression to the mating material is high.

On the other hand, Invention Example No. in which A / (A + B) is 0.20 or more and 0.70 or less. In 4 to 9, since the area ratio of the hard region to the soft region on the surface of the DLC film was optimized, good results were obtained in all aspects of heat resistance, aggression against the mating material, wear resistance, and friction coefficient. Was done.

The sliding member of the present invention can realize all of excellent heat resistance, low aggression against the mating material, high wear resistance, and low friction coefficient.

100 Sliding member 10 Base material 12 Intermediate layer 14 Hard DLC layer 16 Soft DLC layer 18A Hard region 18B Soft region 20 Amorphous carbon film (DLC film)
20A Amorphous carbon film surface (sliding surface)
200 Piston ring 22 Outer peripheral surface of piston ring 24 Inner peripheral surface of piston ring 26A Upper surface (upper side surface) of piston ring
26B Piston ring lower surface (lower side surface)

Claims (4)

With the base material
An amorphous carbon film having a hydrogen content of 3 atomic% or less and a component composition in which the balance is composed of carbon and having a thickness of 3 μm or more, which is formed on the base material and whose surface is a sliding surface.
Have,
The surface of the amorphous carbon film has an arithmetic mean roughness Ra of 0.10 μm or less.
On the surface of the amorphous carbon film, a hard region having an indentation hardness of 25 GPa or more and a soft region having an indentation hardness of 20 GPa or less are mixed.
A sliding member having an A / (A + B) of 0.20 or more and 0.70 or less, where A is an area of a hard region and B is an area of a soft region on the surface. In the amorphous carbon film,
In the portion of the hard region of the surface, only the hard portion exists in the depth direction from the surface.
The sliding member according to claim 1, wherein in the portion of the soft region of the surface, the soft portion is first located in the depth direction from the surface, and then the hard portion is located. One or more elements selected from the group consisting of Cr, Ti, Co, V, Mo, Si and W or carbides, nitrides and carbonitrides thereof between the base material and the amorphous carbon film. The sliding member according to claim 1 or 2, which has an intermediate layer made of. A piston ring made of the sliding member according to any one of claims 1 to 3, wherein the outer peripheral surface thereof is the sliding surface.

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