WO2021140851A1

WO2021140851A1 - Sliding member and piston ring

Info

Publication number: WO2021140851A1
Application number: PCT/JP2020/046832
Authority: WO
Inventors: 正明高谷; シンルイデン; 祐司島
Original assignee: 株式会社リケン
Priority date: 2020-01-10
Filing date: 2020-12-15
Publication date: 2021-07-15
Also published as: JP6938807B1; JPWO2021140851A1

Abstract

Provided is a sliding member which has a DLC film with excellent heat resistance, by which high abrasion resistance can be achieved regardless of whether a lubricating oil contains an organic molybdenum-based compound, and by which a low friction coefficient can be achieved. A sliding member 100 according to the present disclosure has: a substrate 10; and an amorphous carbon film 20 which is formed on the substrate 10 and has a surface 20A as a sliding surface. The present disclosure is characterized in that, on the surface 20A of the amorphous carbon film, a first region 18A having a component composition which does not substantially contain hydrogen and contains 2-20 at% of silicon and 2-15 at% of boron, with the remainder consisting of carbon coexists with a second region 18B having a component composition which does not substantially contain hydrogen and consists of carbon, and when, on the surface 20A, the area of the first region 18A is defined as A, and the area of the second region 18B is defined as B, B/(A+B) is 0.05-0.40.

Description

Sliding members and piston rings

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 coefficient of friction 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. is there.

Patent Document 1 discloses a piston ring formed by coating the outer peripheral surface with a hydrogen-free DLC (ta-C: tetrahedramal aminophorus Carbon) film.

Special Table 2013-528697

As in Patent Document 1, a hydrogen-free DLC film is preferable in that it can avoid deterioration of wear resistance due to hydrogen separation in a high temperature environment. However, since the DLC film contains carbon as a main component, it generally tends to be inferior in heat resistance. That is, the conventional hydrogen-free DLC film has a problem that the hardness decreases in a high temperature environment of 400 ° C. or higher. For example, in the case of a piston ring for a downsizing turbo engine whose fuel efficiency is improved in response to environmental protection, the sliding environment becomes extremely severe due to high temperature and high surface pressure. In recent years, the sliding environment of sliding members other than piston rings has been getting hotter. Therefore, in recent years, the sliding member is desired to have high heat resistance, in which a decrease in hardness of the DLC film can be suppressed even in the above-mentioned high temperature environment. Further, the conventional hydrogen-free DLC film has a problem that when it is slid under a lubricating oil containing an organic molybdenum-based compound, the wear of the DLC film is promoted and sufficient wear resistance cannot be obtained.

As a result of studies by the present inventors to solve these problems, an amorphous carbon film (DLC film) forming a sliding surface of a sliding member is provided with a predetermined amount of silicon (Si) and boron (B). It is said that high heat resistance and high wear resistance under a lubricating oil containing an organic molybdenum-based compound can be realized by adopting a component composition that contains carbon and the balance is substantially free of hydrogen. I got the knowledge of.

However, as a result of further studies by the present inventors, in the case of the above-mentioned Si-B-containing hydrogen-free DLC film, high abrasion resistance cannot be obtained under a lubricating oil containing no organic molybdenum compound. Further, it was found that graphitization due to sliding heat is less likely to be promoted, and it is difficult to obtain a low friction coefficient.

Therefore, in view of the above problems, the present invention has a DLC film having excellent heat resistance, can obtain high wear resistance regardless of whether or not the lubricating oil contains an organic molybdenum compound, and has a lower friction coefficient. It is an object of the present invention to provide a sliding member capable of realizing the above.

As a result of diligent studies by the present inventors in order to solve the above problems, a first region containing a predetermined amount of Si and B, and Si and B were formed on the surface of a hydrogen-free amorphous carbon film (DLC film). By mixing the second region consisting of only C without containing it, and setting the area ratio of the first region and the second region on the surface within a predetermined range, it depends on the heat resistance and the type of lubricating oil. It has been found that all the properties of no high wear resistance and low friction coefficient 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 formed on the base material and whose surface is a sliding surface,
Have,
The surface of the amorphous carbon film contains silicon: 2 atomic% or more and 20 atomic% or less, and boron: 2 atomic% or more and 15 atomic% or less, and the balance is carbon, which is substantially hydrogen-free. The first region having a composition and the second region having a component composition consisting of carbon and substantially free of hydrogen are mixed.
A sliding member having a B / (A + B) of 0.05 or more and 0.40 or less, where A is the area of the first region and B is the area of the second region on the surface.

(2) When the thickness of the amorphous carbon film is 20 μm or less, the thickness of the amorphous carbon film exceeds 20 μm in the entire range in the thickness direction of the amorphous carbon film. The first region and the second region are mixed in a cross section perpendicular to the thickness direction in a range of at least 20 μm from the surface of the amorphous carbon film in the thickness direction, and the first region in the cross section. The sliding member according to (1) above, wherein B'/ (A'+ B') is 0.05 or more and 0.40 or less, where A'is the area of A'and the area of the second region is B'.

(3) The sliding member according to (1) or (2) above, wherein the component composition of the first region further contains at least one of nitrogen: 15 atomic% or less and oxygen: 15 atomic% or less.

(4) The sliding member according to any one of (1) to (3) above, wherein the indentation hardness of the first region is smaller than the indentation hardness of the second region.

(5) The sliding member according to any one of (1) to (4) above, wherein the thickness of the amorphous carbon film is 0.5 μm or more and 50 μm or less.

(6) 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 any one of (1) to (5) above, which has an intermediate layer made of carbide.

(7) A piston ring made of the sliding member according to any one of (1) to (6) above, the outer peripheral surface of which is the sliding surface.

The sliding member of the present invention has a DLC film having excellent heat resistance, can obtain high wear resistance regardless of whether or not the lubricating oil contains an organic molybdenum compound, and realizes a further low coefficient of friction. It is possible to do.

It is a schematic cross-sectional view of the sliding member 100 by 1st Embodiment of this invention. It is a figure which schematically explains a part of the manufacturing process of the sliding member 100 by 1st Embodiment of this invention. It is a schematic cross-sectional view of the sliding member 200 according to the 2nd Embodiment of this invention. It is sectional drawing of the piston ring 300 by one Embodiment of this invention. It is an SEM image of the surface of the DLC film in the invention example (No. 4) of Table 1. FIG. It is a schematic diagram which shows the form of the reciprocating sliding test. It is a schematic diagram explaining the calculation method of the wear depth.

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

With reference to FIG. 3, the sliding member 200 according to the second embodiment of the present invention is used under lubricating oil, and has a base material 10 and a surface 30A formed on the base material 10. It has an amorphous carbon film (DLC film) 30 as a sliding surface. Further, optionally, an intermediate layer (not shown) may be provided between the base material 10 and the amorphous carbon film 30.

The sliding

members

100 and 200 according to the present embodiment are used in the presence of a lubricating oil containing an organic molybdenum compound or in the presence of a lubricating oil containing no organic molybdenum compound. That is, the use of the sliding

members

100 and 200 in combination with a lubricating oil containing an organic molybdenum compound or a lubricating oil not containing an organic molybdenum compound also constitutes the present invention. Further, the sliding

members

100 and 200, an arbitrary mating sliding member, and a lubricating oil containing an organic molybdenum-based compound or a lubricating oil containing no organic molybdenum-based compound supplied to the sliding surfaces of both of them. A sliding structure including the above also constitutes the present invention.

The organic molybdenum-based compound is preferably one or more organic molybdenum-based compounds selected from molybdenum dithiocarbamate (Mo-DTC) and molybdenum dithiophosphate (Mo-DTP). These organic molybdenum compounds can be decomposed by heat due to sliding to form a tribo film of _{molybdenum disulfide (MoS 2) on the sliding surface of the mating material that slides with the DLC film.}

[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

members

100 and 200 of the present embodiment are used as 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

members

100 and 200 of the present embodiment are used as 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, the material of the base material 10 is an aluminum alloy or the like. Can be mentioned.

When applied to the first embodiment, the roughness of the surface of the base material 10 (the surface forming the DLC film) 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 first DLC layer 14 and the second DLC layer 16 (see FIGS. 1 and 2) having appropriate surface roughness described later are formed. Because it cannot be done. The upper limit of the surface roughness of the base material 10 applied to the first embodiment is not particularly limited, but the surface roughness of the base material 10 is 0.15 μm or less in Ra in consideration of the polishing allowance of the final surface polishing. Is preferable. 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. When applied to the second embodiment, the surface roughness of the base material 10 is not particularly limited, but it can be the same as when applied to the first embodiment.

"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 by being formed between the base material 10 and the

DLC films

20 and 30, and enhancing the adhesion of the

DLC films

20 and 30. 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 films

20 and 30, 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 films

20 and 30, the thickness of the intermediate layer 12 is preferably 0.6 μm or less, and is 0. More preferably, it is 5.5 μm or less.

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]
With reference to FIG. 1, the DLC film 20 applied to the first embodiment is formed on the surface of the base material 10 when the intermediate layer 12 is not formed, and when the intermediate layer 12 is formed, the DLC film 20 is formed on the surface of the base material 10. , Formed on the surface of the intermediate layer 12. As shown in FIG. 1, the DLC film 20 is composed of a first DLC layer (Si—B-containing H-free DLC layer) 14 containing a predetermined amount of Si and B, and a second DLC containing only C without containing Si and B. The layers (H-free DLC layer) 16 are alternately laminated a plurality of times while having a predetermined surface roughness. Then, referring to FIG. 2 in addition to FIG. 1, the surface of the uppermost second DLC layer (H-free DLC layer) 16 having a predetermined surface roughness is polished by a predetermined amount to form the DLC film 20. The first DLC layer (Si—B-containing H-free DLC layer) 14 is exposed on the surface 20A, and the first region (Si—B-containing region) 18A and the second DLC layer (H-free DLC layer) 16 remain. The second region (ta-C region) 18B is mixed.

Although FIGS. 1 and 2 show an example in which the uppermost layer is the second DLC layer 16, the present invention is not limited to this, and the uppermost layer may be the first DLC layer 14. In that case, a DLC film 20 is formed by polishing the surface of the uppermost first DLC layer 14 having a predetermined surface roughness by a predetermined amount, and the first DLC layer (Si—B-containing H) is formed on the surface 20A. The first region (Si—B-containing region) 18A in which the free DLC layer (14) remains and the second region (ta-C region) 18B in which the second DLC layer (H-free DLC layer) 16 is exposed are mixed. Become.

The lowermost layer is not particularly limited, and may be the first DLC layer 14 or the second DLC layer 16.

With reference to FIG. 3, the DLC film 30 applied to the second embodiment is formed on the surface of the base material 10 when the intermediate layer is not formed, and is intermediate when the intermediate layer is formed. Formed on the surface of the layer. As shown in FIG. 3, the DLC film 30 is composed of only C without containing Si and B, using the first DLC portion (Si—B-containing H-free DLC portion) 24 containing a predetermined amount of Si and B as a matrix. The second DLC part (H-free DLC part) 26 has a film structure dispersed in the matrix. The surface of the DLC film 30 has been polished by a predetermined amount, and as a result, the first region (Si-) in which the first DLC portion (Si—B-containing H-free DLC portion) 24 is exposed on the surface 30A of the DLC film 30. The B-containing region) 28A and the second region (ta-C region) 28B where the second DLC portion (H-free DLC portion) 26 is exposed are mixed.

<Component composition of 1st DLC layer / 1st DLC part>
The first DLC layer 14 and the first DLC part 24 contain silicon: 2 atomic% or more and 20 atomic% or less, and boron: 2 atomic% or more and 15 atomic% or less, and the balance is carbon and is substantially hydrogen-free. Has. The first DLC layer 14 and the first DLC unit 24 preferably further contain a predetermined amount of one or both of nitrogen (N) and oxygen (O). The fact that it is amorphous carbon can be confirmed by Raman spectrum measurement using a Raman spectrophotometer (Ar laser). By having such a component composition, the first DLC layer 14 and the first DLC part 24 are improved in the heat resistance of the

DLC films

20 and 30 and the wear resistance under the lubricating oil containing the organic molybdenum compound. Contribute. The present inventors consider the action of obtaining such an effect as follows.

Generally, in the presence of a lubricating oil containing an organic molybdenum compound, the carbon dangling bond in the DLC film and Mo in the lubricating oil combine to form hard molybdenum carbide (MoC) particles. The MoC particles accelerate the wear of the DLC film. On the other hand, in the present embodiment, since the first DLC layer 14 and the first DLC part 24 contain a predetermined amount of Si and B, the dangling bond density of carbon in the first DLC layer 14 and the first DLC part 24 is reduced. As a result, the formation of hard MoC particles is suppressed. As a result, high wear resistance can be obtained under a lubricating oil containing an organic molybdenum compound.

Further, when the first DLC layer 14 and the first DLC unit 24 contain a predetermined amount of Si and B, the first DLC layer 14 is exposed as a sliding surface due to the reaction of Si and B with oxygen in a high temperature environment. _{It is considered that a dense SiO 2} film and a B ₂ O ₃ film are formed on the surface of the first DLC portion 24, and these films function as protective films to improve heat resistance.

When the Si content is less than 2 atomic%, or when the B content is less than 2 atomic%, the effect of improving heat resistance due to the above action and improving wear resistance under lubricating oil containing an organic molybdenum compound is effective. Cannot be obtained sufficiently. Therefore, the Si content is preferably 2 atomic% or more and 5 atomic% or more, the B content is preferably 2 atomic% or more and 5 atomic% or more, and the Si content and B content. The total of is preferably 10 atomic% or more.

When the Si content exceeds 20 atomic%, the sp ³ bond of carbon is significantly reduced, so that a DLC film having a desired hardness cannot be obtained, and both heat resistance and wear resistance deteriorate. When the B content exceeds 15 atomic%, the discharge of the C / B alloy cathode becomes very unstable, so that a DLC film having a desired hardness cannot be obtained, and both heat resistance and wear resistance deteriorate. .. Therefore, the Si content is preferably 20 atomic% or less and preferably 15 atomic% or less, and the B content is preferably 15 atomic% or less and preferably 12 atomic% or less, and is preferably 10 atomic% or less. Is more preferable. The total of the Si content and the B content is preferably 30 atomic% or less.

When the first DLC layer 14 and the first DLC part 24 contain hydrogen, when the temperature of the first DLC layer 14 and the first DLC part 24 becomes high due to sliding, hydrogen is desorbed and the first DLC layer 14 and the first DLC part 24 deteriorate. As a result, wear of the first DLC layer 14 and the first DLC portion 24 is promoted. Therefore, it is assumed that the first DLC layer 14 and the first DLC unit 24 do not substantially contain hydrogen. This makes it possible to avoid deterioration of wear resistance due to the release of hydrogen in a high temperature environment. Here, "substantially free of hydrogen" as used herein means that the hydrogen content in the first DLC layer 14 and the first DLC unit 24 is 3 atomic% or less.

The first DLC layer 14 and the first DLC unit 24 may contain nitrogen (N). By containing N, a BN bond and a Si—N bond are formed. Since BN has a layered lattice structure with low shear resistance, it exhibits a friction reducing effect, and Si ₃ N ₄ has excellent fracture toughness, which contributes to improvement of wear resistance. From this viewpoint, the N content is preferably 5 atomic% or more. However, when the N content exceeds 15 atomic%, ^{the formation of the sp 3} bond of carbon is inhibited, so that the first DLC layer and the first DLC portion having the desired hardness cannot be obtained, and the heat resistance and wear resistance Both deteriorate. Therefore, when the first DLC layer 14 and the first DLC unit 24 contain nitrogen, the N content thereof is 15 atomic% or less, preferably 12 atomic% or less.

The first DLC layer 14 and the first DLC unit 24 may contain oxygen (O). By containing O, when the surfaces of the first DLC layer 14 and the first DLC portion 24 become hot due to sliding, oxide layers of SiO ₂ and B ₂ O ₃ are likely to be formed, and the oxide layers of SiO 2 and B 2 O 3 are easily formed in the lubricating oil. _{As a result of promoting the production of MoS 2} by the decomposition / sulfurization reaction of the organic molybdenum compound, the lubricity is improved, and low friction and high wear resistance can be realized. From this point of view, the O content is preferably 2 atomic% or more. However, when the O content exceeds 15 atomic%, the COC bond and the C = O bond increase, the densities of the first DLC layer and the first DLC portion decrease, and both heat resistance and abrasion resistance deteriorate. Therefore, when the first DLC layer 14 and the first DLC unit 24 contain oxygen, the O content thereof is set to 15 atomic% or less.

Further, from the viewpoint of achieving high wear resistance while maintaining a low friction coefficient, the total content of nitrogen and oxygen is preferably 15 atomic% or less.

<Component composition of 2nd DLC layer / 2nd DLC part>
The second DLC layer 16 and the second DLC portion 26 have a substantially hydrogen-free component composition composed of carbon. The fact that it is amorphous carbon can be confirmed by Raman spectrum measurement using a Raman spectrophotometer (Ar laser). By having such a component composition, the second DLC layer 16 and the second DLC portion 26 contribute to the improvement of the wear resistance under the lubricating oil containing no organic molybdenum compound and the reduction of the friction coefficient. The present inventors consider the action of obtaining such an effect as follows.

Since the second DLC layer 16 and the second DLC portion 26 are substantially composed of carbon only, graphitization due to sliding heat is promoted, which contributes to a decrease in the friction coefficient. Further, by reducing the friction coefficient, the sliding load is reduced, and the amount of wear is suppressed under the lubricating oil containing no organic molybdenum compound.

Similar to the first DLC layer 14 and the first DLC section 24, the second DLC layer 16 and the second DLC section 26 are also substantially free of hydrogen. This makes it possible to avoid deterioration of wear resistance due to the release of hydrogen in a high temperature environment. Here, "substantially free of hydrogen" as used herein means that the hydrogen content in the second DLC layer 16 and the second DLC section 26 is 3 atomic% or less.

<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.

<Measuring method of Si, B, N and O contents of the first DLC layer / first DLC part>
The Si, B, N and O contents of the first DLC layer and the first DLC part shall be measured by X-ray photoelectron spectroscopy (XPS) under the following conditions. Quantitative analysis of elements in XPS is performed based on the photoelectron peak area. Since the peak area is proportional to the atomic concentration and the sensitivity of the electron of interest, the value obtained by dividing the peak area by the relative sensitivity coefficient is proportional to the atomic concentration. Therefore, relative quantification can be performed with the sum of the quantified values of each element as 100 atomic%.
-Measuring device: QuanteraSXM manufactured by PHI
-X-ray source: Monochromatic Al (1486.6 eV)
・ Detection area: 100 μmφ
-Detection depth: Approximately 4 to 5 nm (extraction angle 45 °)
-Measurement spectrum: wide, C1s, Si2p, B1s, N1s, O1s

<Composite ratio of first region and second region on the surface of DLC film>
With reference to FIGS. 1 and 2, in the first embodiment, the first region (Si—B-containing region) 18A and the second region (ta-C region) 18B are mixed on the surface 20A of the DLC film 20. deep. Further, referring to FIG. 3, also in the second embodiment, the first region (Si—B containing region) 28A and the second region (taC region) 28B are mixed on the surface 30A of the DLC film 30. .. Then, assuming that the area of the first region on the

surfaces

20A and 30A is A and the area of the second region is B, B / (A + B) is 0.05 or more and 0.40 or less, that is, the first region (Si−). It is important to combine the second region (ta-C region) 18B and 28A at a predetermined ratio while mainly containing the B-containing region) 18A and 28A.

When B / (A + B) is less than 0.05, the second regions (ta-C regions) 18B and 28B are too small on the

surfaces

20A and 30A of the DLC film, and the first regions (Si-B-containing regions) 18A, 28A is excessive. In this case, the wear resistance under the lubricating oil containing no organic molybdenum compound becomes insufficient, and a low coefficient of friction cannot be obtained. Therefore, B / (A + B) is set to 0.05 or more, preferably 0.10 or more.

When B / (A + B) exceeds 0.40, the first region (Si—B-containing region) 18A and 28A is too small on the

surfaces

20A and 30A of the DLC film, and the second region (ta-C region) 18B, 28B is excessive. In this case, the heat resistance and the wear resistance under the lubricating oil containing the organic molybdenum compound become insufficient. Therefore, B / (A + B) is set to 0.40 or less, preferably 0.35 or less.

B / (A + B) shall be calculated by the following method. As illustrated in FIG. 5, the first region (Si-B-containing region) and the second region (Ta-C region) are different in the scanning electron microscope (SEM) due to the presence or absence of Si and B. It can be observed as a contrast. Therefore, the area of each region in the field of view can be calculated by analyzing the obtained image and binarizing it. Specifically, any three places on the surface of the DLC film are observed by FE-SEM, and a secondary electron image is taken. The observation conditions are an acceleration voltage of 5 kV and a magnification of 10,000 times. The captured image is binarized by image analysis software, the area of the first region is V1, the area of the second region is V2, V2 / (V1 + V2) is obtained for each captured image, and the obtained three values are countable. On average, it is B / (A + B).

The fact that the

first regions

18A and 28A and the

second regions

18B and 28B are "mixed" on the

surfaces

20A and 30A of the DLC film means that the

first regions

18A and 28A and the second regions 18B are on the

surfaces

20A and 30A of the DLC film. , 28B are distributed and exist.

<Indentation hardness of the first region and the second region>
The indentation hardness of the

first regions

18A and 28A is smaller than the indentation hardness of the

second regions

18B and 28B.

The indentation hardness of the

first regions

18A and 28A is preferably 15 GPa or more and 35 GPa or less. When the indentation hardness is 15 GPa or more, the wear resistance of the DLC film is not insufficient. On the other hand, when the indentation hardness is 35 GPa or less, the toughness of the DLC film is not insufficient, and chipping and peeling are unlikely to occur.

The indentation hardness of the

second regions

18B and 28B is preferably 25 GPa or more and 50 GPa or less. If the indentation hardness is 25 GPa or more, the wear resistance and heat resistance of the DLC film will not be insufficient. On the other hand, when the indentation hardness is 50 GPa or less, the load of finishing is not increased, so that the cost increase can be suppressed.

<Thickness of DLC film>
The thickness of the

DLC films

20 and 30 is not particularly limited, but is preferably 0.5 μm or more and 50 μm or less. This is because if the thickness is 0.5 μm or more, the durability of the DLC film is not insufficient, and if it is 50 μm or less, the adhesion to the base material is insufficient and peeling does not occur. In the present invention, the thickness of the DLC film shall be measured by carotest or by observing the cross section of the resin-embedded film.

<Morphology of DLC film in the thickness direction>
From the viewpoint of maintaining the effect of the present invention in the sliding process, when the thickness of the

DLC films

20 and 30 is 20 μm or less, the entire range of the

DLC films

20 and 30 in the thickness direction and the

DLC films

20 and 30 When the thickness of the DLC film exceeds 20 μm, the

first regions

18A and 28A and the

second regions

18B and 28B are formed in a cross section perpendicular to the thickness direction in a range of at least 20 μm in the thickness direction from the

surfaces

20A and 30A of the DLC film. It is mixed, and the state where B'/ (A'+ B') is 0.05 or more and 0.40 or less is maintained, where A'is the area of the first region and B'is the area of the second region in the cross section. It is preferable to be done.

Note that B'/ (A'+ B') shall be obtained according to the above-mentioned method for obtaining B / (A + B). Specifically, when the thickness of the DLC film is 20 μm or less, the DLC film is polished to form a first sample having a polished surface in which 45 to 55% of the thickness is exposed from the surface of the DLC film. Prepare a second sample with a polished surface that is 80-90% exposed from the surface of the DLC film. The polished surface of the first sample and the polished surface of the second sample are each observed by FE-SEM, and a secondary electron image is taken. The captured image is binarized by image analysis software, the area of the first region is V1', the area of the second region is V2', and V2'/ (V1'+ V2') is obtained in each captured image and obtained. The three values are countably averaged to obtain B'/ (A'+ B'). If B'/ (A'+ B') is 0.05 or more and 0.40 or less in both the first sample and the second sample, B'/ (A) in the entire range in the thickness direction of the DLC film. It is considered that the state in which'+ B') is 0.05 or more and 0.40 or less is maintained.

When the thickness of the DLC film exceeds 20 μm, the DLC film is polished to have a first sample having a polished surface where a position of 10 μm from the surface of the DLC film is exposed in the thickness direction, and a first sample having a polished surface and a thickness direction from the surface of the DLC film. Prepare a second sample with a polished surface exposed at a position of 20 μm. The polished surface of the first sample and the polished surface of the second sample are each observed by FE-SEM, and a secondary electron image is taken. The captured image is binarized by image analysis software, the area of the first region is V1', the area of the second region is V2', and V2'/ (V1'+ V2') is obtained in each captured image and obtained. The three values are countably averaged to obtain B'/ (A'+ B'). If B'/ (A'+ B') is 0.05 or more and 0.40 or less in both the first sample and the second sample, B is in the range of at least 20 μm in the thickness direction from the surface of the DLC film. It is considered that the state in which'/ (A'+ B') is 0.05 or more and 0.40 or less is maintained.

<Surface roughness and thickness of the first DLC layer and the second DLC layer>
In the first embodiment, with reference to FIG. 1, as described above, B / (A + B) on the surface 20A of the DLC film satisfies 0.05 or more and 0.40 or less, and in the thickness direction of the DLC film. In order to maintain the state where B'/ (A'+ B') is 0.05 or more and 0.40 or less, the first DLC layer 14 and the second DLC layer 16 to be laminated have a predetermined surface roughness and , Must have a predetermined thickness.

From this point of view, the surface roughness of each of the first DLC layer 14 and the second DLC layer 16 is preferably 0.01 μm or more and 0.15 μm or less in terms of arithmetic mean roughness Ra. By controlling the surface roughness within this range, as a result of the polishing process described later, it becomes easy to realize the desired B / (A + B), and it becomes easy to maintain the desired B'/ (A'+ B'). Because. "Ra on the surface of each DLC layer" shall be measured by the following method. That is, a cross-sectional sample in the thickness direction of the DLC film is produced by focused ion beam (FIB) processing, a transmission electron microscope image (TEM image) is observed, and the adjacent TEM image is adjacent based on the change in brightness of the obtained TEM image. Determine the boundary between layers. Specifically, the surface shape (cross-sectional shape) of each DLC layer is defined as the boundary between adjacent layers where the change in brightness is halved. Based on the cross-sectional shape of each DLC layer obtained, the arithmetic average roughness Ra is obtained according to JIS B0601 (2001) using surface roughness measurement software or the like. The measurement shall be performed three times, and the average value of the three times shall be adopted.

Further, the thickness and the thickness ratio of each of the first DLC layer 14 and the second DLC layer 16 are not particularly limited, but a desired B / (A + B) is realized and a desired B'/ (A'+ B') is realized. ) Can be maintained as appropriate.

<Mixing ratio of 1st DLC part / 2nd DLC part>
In the second embodiment, with reference to FIG. 3, as described above, B / (A + B) on the surface 30A of the DLC film satisfies 0.05 or more and 0.40 or less, and in the thickness direction of the DLC film. In order to maintain the state where B'/ (A'+ B') is 0.05 or more and 0.40 or less, the first DLC part 24 and the second DLC part 26 in the DLC film 30 are controlled by controlling the manufacturing conditions described later. The mixing ratio of the above may be adjusted as appropriate.

<Surface roughness of DLC film>
The surface roughness of the

DLC films

20 and 30 is preferably 0.1 μm or less in terms of arithmetic mean roughness Ra. As a result, the aggression of the DLC film to the mating material can be reduced. 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 dimension 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.

<Method of forming DLC film>
The

DLC films

20 and 30 can be formed by using a PVD method such as ion plating by vacuum arc discharge (VA method) using a carbon target, for example. 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 by using the ion plating method by vacuum arc discharge, its hardness can be adjusted by a bias voltage applied to the base material or the like. 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.

A carbon alloy target containing Si and B can be used for film formation of the first DLC layer (Si—B-containing H-free DLC layer) 14 and the first DLC portion (Si—B-containing H-free DLC portion) 24. That is, in order for the first DLC layer 14 and the first DLC portion 24 to contain a predetermined amount of Si and B, for example, _{graphite containing silicon carbide (SiC) and boron carbide (B 4} C) is used as the cathode material. By adjusting these contents in the cathode material, the Si content and the B content in the first DLC layer 14 and the first DLC unit 24 can be controlled. Further, in order to contain a predetermined amount of N and O in the first DLC layer 14 and the first DLC unit 24, N and O may be added to the carbon alloy target.

A carbon target containing no Si and B can be used for film formation of the second DLC layer (H-free DLC layer) 16 and the second DLC part (H-free DLC part) 26.

In the first embodiment, when forming the DLC film 20 having a laminated structure, first, a base material 10 having a surface roughness of 0.01 μm or more is prepared, and an intermediate layer 12 is optionally formed on the surface. To do. After that, a plurality of sets of a first DLC layer (Si—B-containing H-free DLC layer) 14 and a second DLC layer (H-free DLC layer) 16 are alternately arranged on the surface of the base material 10 or the surface of the intermediate layer 12. Laminate. At that time, the surface of the base material 10 is provided with a predetermined surface roughness, and carbon fine particles (droplets) and the like are incorporated into the film in the process of film formation, so that the first DLC layer 14 and the first DLC layer 14 A predetermined surface roughness is provided on each surface of the 2DLC layer 16.

The laminated structure of the first DLC layer 14 and the second DLC layer 16 is a group that rotates a Si—B-containing carbon alloy target for forming the first DLC layer 14 and a carbon target for forming the second DLC layer 16. It can be obtained by arranging the base material in a concentric circle around the material. For example, if the Si—B-containing carbon alloy target and the carbon target are arranged so as to be offset by 180 °, a laminated structure of the first DLC layer 14 and the second DLC layer 16 can be obtained. The thickness ratio of the first DLC layer 14 and the second DLC layer 16 can be controlled by adjusting the rotation speed of the base material and the target discharge current.

Next, the surface of the uppermost second DLC layer 16 or the first DLC layer 14 is polished to form the DLC film 20. By adjusting the polishing amount at that time, B / (A + B) is controlled in the range of 0.05 or more and 0.40 or less.

In the second embodiment, when the DLC film 30 having a dispersed structure is formed, a Si—B-containing carbon alloy target for forming the first DLC portion 24 and a carbon target for forming the second DLC portion 26 are used. , It can be obtained by arranging the rotating base material in a concentric circle around the base material. At that time, if the Si—B-containing carbon alloy target and the carbon target are arranged close to each other, a film structure in which the second DLC portion 26 is dispersed in the matrix of the first DLC portion 24 can be obtained. The dispersion ratio of the first DLC unit 24 and the second DLC unit 26 can be controlled by adjusting the rotation speed of the base material and the target discharge current.

In this way, the

hard regions

18A and 28A and the

soft regions

18B and 28B can be mixed on the

surfaces

20A and 30A of the

DLC coatings

20 and 30, and B' The state in which / (A'+ B') is 0.05 or more and 0.40 or less can be maintained.

[Application of sliding members]
The sliding

members

100 and 200 according to one embodiment of the present invention include a piston ring, a piston, a piston pin, a tappet, a valve lifter, a shim, and a rocker arm used for a sliding portion of an internal combustion engine in which lubricating oil such as engine oil is interposed. , Cams, 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. 4, the piston ring 300 according to the embodiment of the present invention has a ring shape with four surfaces of an outer peripheral surface 32, an inner peripheral surface 34, and upper and

lower surfaces

36A and 36B, and the outer peripheral surface 32 is shown in FIG. It is formed by the DLC film 20 shown or the DLC film 30 shown in FIG. That is, the piston ring 300 of the present embodiment is composed of the sliding member 100 or the sliding member 200, and its outer peripheral surface 22 is the surface 20A of the DLC film shown in FIG. 1 or the surface of the DLC film shown in FIG. It becomes 30A. As a result, excellent heat resistance can be obtained on the outer peripheral surface 22 which is a sliding surface, and high wear resistance can be obtained regardless of whether or not the lubricating oil contains an organic molybdenum compound, which is even lower. It is possible to achieve a coefficient of friction.

[Production of sample]
DLC films of various examples shown in Table 1 were formed on the surface of a base material (surface roughness Ra: 0.01 μm) which is a columnar body (φ6 mm × height 14 mm) of SUJ2 material (JIS G 4805). A sliding member was obtained. In Nos. 4 and 5, the intermediate layer shown in Table 1 was formed on the surface of the base material, and the DLC film shown in Table 1 was formed on the intermediate layer to obtain a sliding member. For the formation of the DLC film, a film forming apparatus by a vacuum arc method was used. Specifically, containing silicon carbide (SiC) and boron carbide (B ₄ C), and Si-B-containing carbon alloy target made of graphite, was prepared a carbon target containing no Si and B. The Si—B-containing carbon alloy target and the carbon target were arranged around the rotating base material in a concentric circle centered on the base material, shifted by 180 °. In this way, a DLC film having a laminated structure of a first DLC layer and a second DLC layer was formed. The surface of the DLC film was polished by a predetermined amount to reduce Ra to 0.1 μm or less. The thickness ratio of the first DLC layer and the second DLC layer is controlled by adjusting the target discharge current, and by variously changing this thickness ratio, B / (A + B) and B'/ ( A'+ B') was controlled. In some examples (Nos. 11 to 13), one or both of nitrogen and oxygen were further contained in the Si—B-containing carbon alloy target for forming the first DLC layer. No. In No. 14, a first DLC layer was formed using a B-containing carbon alloy target containing boron carbide (B _{4 C) and made of graphite.} In No. 15, a first DLC layer was formed using a Si-containing carbon alloy target containing silicon carbide (SiC) and made of graphite.

In each example, the Si content, B content, N content, and O content of the first DLC layer were determined by the methods described above and are shown in Table 1. The thickness of the DLC film was measured by the Carotest and is shown in Table 1. The B / (A + B) on the surface of the DLC film was determined by the method described above and is shown in Table 1. For B'/ (A'+ B'), the values of the first sample and the second sample were obtained by the method described above, and are shown in Table 1. In addition, the indentation hardness of the first region and the second region was measured and shown in Table 1. The indentation hardness was measured using an ultra-fine 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.

[Evaluation of heat resistance]
Two samples were prepared for each example in Table 1. The first sample was heat-treated in an atmosphere of 400 ° C. for 5 hours, and the second sample was heat-treated in an atmosphere of 500 ° C. for 5 hours. For each sample, the indentation hardness of the DLC film was measured before and after the heat treatment. The indentation hardness was measured using an ultra-fine indentation hardness tester manufactured by Elionix Inc. As a condition, using a Belkovic indenter, the pushing region is the first region (Si-B containing region) and the second region (ta-) under a load such that the pushing depth is about 1/10 of the thickness of the DLC film. The test was carried out under the condition including both of C region). The results are shown in Table 2. Table 2 shows the reduction rate of the hardness after the heat treatment with respect to the hardness before the heat treatment.

[Evaluation of wear resistance and friction coefficient]
A SUJ2 material (JIS G 4805) disc (φ25 mm × t8 mm) was prepared as the sliding mating material, and the sliding members of each example were subjected to the vibration friction and wear test (Optimor: SRV test) whose schematic diagram is shown in FIG. The reciprocating test was conducted under the following test conditions.
Test time: 60 min
Load: 500N
Reciprocating frequency: 50Hz
Amplitude: 3 mm
Lubricating oil: (1) Base oil PAO
(2) Engine oil 0W-8 (Mo-DTC additive-free oil)
(3) Engine oil 0W-8 (Mo-DTC added oil)
(4) Engine oil 0W-20 (Mo-DTC additive-free oil)
(5) Engine oil 0W-20 (Mo-DTC added oil)
Lubricating oil temperature: 80 ° C

For each example shown in Table 1, the coefficient of friction at the end of the test was read from the SRV tester. Further, for each example shown in Table 1, the sliding mark width a is measured with an optical microscope for the sliding member after the test is completed with reference to FIG. 7, and the wear depth d is calculated based on the following formula. did. The results are shown in Table 2. The wear depth in Table 2 is based on Comparative Example No. It is shown as a relative ratio with 13.
Wear depth d = r- (r ^2- a ² ) ^1/2

100 Sliding member 10 Base material 12 Intermediate layer 14 First DLC layer (Si-B-containing H-free DLC layer)
16 Second DLC layer (H-free DLC layer)
18A 1st region (Si-B containing region)
18B second region (ta-C region)
20 Amorphous carbon film (DLC film)
20A Amorphous carbon film surface (sliding surface)
200 Sliding member 24 1st DLC part (Si-B-containing H-free DLC part)
26 Second DLC section (H-free DLC section)
28A 1st region (Si-B containing region)
28B second region (ta-C region)
30 Amorphous carbon film (DLC film)
30A Amorphous carbon film surface (sliding surface)
300 Piston ring 32 Outer peripheral surface of piston ring 34 Inner peripheral surface of piston ring 36A Upper surface (upper side surface) of piston ring
36B Piston ring lower surface (lower side surface)

Claims

With the base material
An amorphous carbon film formed on the base material and whose surface is a sliding surface,
Have,
The surface of the amorphous carbon film contains silicon: 2 atomic% or more and 20 atomic% or less, and boron: 2 atomic% or more and 15 atomic% or less, and the balance is carbon, which is substantially hydrogen-free. The first region having a composition and the second region having a component composition consisting of carbon and substantially free of hydrogen are mixed.
A sliding member having a B / (A + B) of 0.05 or more and 0.40 or less, where A is the area of the first region and B is the area of the second region on the surface.
When the thickness of the amorphous carbon film is 20 μm or less, the amorphous carbon film is in the entire thickness direction of the thickness direction, and when the thickness of the amorphous carbon film is more than 20 μm, the amorphous carbon film is said to be amorphous. In the range of at least 20 μm in the thickness direction from the surface of the quality carbon film, the first region and the second region are mixed in the cross section perpendicular to the thickness direction, and the area of the first region in the cross section is defined. The sliding member according to claim 1, wherein A', the area of the second region is B', and B'/ (A'+ B') is 0.05 or more and 0.40 or less.
The sliding member according to claim 1 or 2, wherein the component composition of the first region further contains at least one of nitrogen: 15 atomic% or less and oxygen: 15 atomic% or less.
The sliding member according to any one of claims 1 to 3, wherein the indentation hardness of the first region is smaller than the indentation hardness of the second region.
The sliding member according to any one of claims 1 to 4, wherein the thickness of the amorphous carbon film is 0.5 μm or more and 50 μm or less.
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 any one of claims 1 to 5, which has an intermediate layer made of.
A piston ring made of the sliding member according to any one of claims 1 to 6, wherein the outer peripheral surface thereof is the sliding surface.