阅读说明：本技术 滑动构件及包覆膜 (Sliding member and coating film ) 是由 冈崎孝弘 伊东义洋 杉浦宏幸 金泽信哉 森口秀树 柴田明宣 大城竹彦 于 2018-06-15 设计创作，主要内容包括：本发明的课题是提供具有示出一定且稳定的抗削性和耐磨损性、并且耐剥离性(密合性)优异的包覆膜的滑动构件、及该包覆膜。其解决方法是滑动构件(10),其在基材(11)的滑动面(16)具有由硬质碳层形成的包覆膜(1),上述包覆膜(1)如下所述地构成：通过明视野TEM图像观察包覆膜(1)的剖面时,包含相对地由黑色表示的黑色硬质碳层(B)和相对地由白色表示的白色硬质碳层(W)的重复单元在厚度方向上层叠,且具有1μm～50μm的范围内的厚度,包覆膜(1)具有设置于基材侧的倾斜区域(2)和设置于滑动构件(10)的表面侧的均质区域(3),在上述倾斜区域(2),重复单元中的白色硬质碳层(W)的厚度在厚度方向上逐渐变大,在上述均质区域(3),重复单元中的白色硬质碳层(W)的厚度在厚度方向上相同或大致相同,从而解决了上述问题。(The present invention addresses the problem of providing a sliding member having a coating film that exhibits constant and stable chipping resistance and wear resistance and that has excellent peeling resistance (adhesion), and also providing such a coating film. The sliding member (10) is provided with a coating film (1) formed by a hard carbon layer on a sliding surface (16) of a substrate (11), wherein the coating film (1) is composed of the following components: when a cross section of a coating film (1) is observed through a bright field TEM image, repeating units comprising a black hard carbon layer (B) relatively represented by black and a white hard carbon layer (W) relatively represented by white are laminated in the thickness direction, and have a thickness within the range of 1-50 [ mu ] m, the coating film (1) has an inclined region (2) arranged on the substrate side and a homogeneous region (3) arranged on the surface side of a sliding member (10), the thickness of the white hard carbon layer (W) in the repeating units is gradually increased in the thickness direction in the inclined region (2), and the thickness of the white hard carbon layer (W) in the repeating units is the same or approximately the same in the thickness direction in the homogeneous region (3), thereby solving the problems.)

1. A sliding member having a coating film formed of a hard carbon layer on a sliding surface,

when a cross section of the coating film is observed by a bright field TEM image, repeating units comprising a black hard carbon layer relatively represented by black and a white hard carbon layer relatively represented by white are laminated in a thickness direction, and have a thickness in a range of 1 to 50 [ mu ] m,

the coating film has an inclined region provided on the substrate side and a homogeneous region provided on the surface side, the white hard carbon layer in the repeating unit has a thickness that gradually increases in the thickness direction in the inclined region, the white hard carbon layer in the repeating unit has the same or substantially the same thickness in the thickness direction in the homogeneous region, the inclined region has a form that grows in a V-shape or a radial shape in the thickness direction, and the homogeneous region does not have a form that grows in a V-shape or a radial shape in the thickness direction.

2. The slide member according to claim 1,

the ratio of the thickness of the black hard carbon layer to the thickness of the white hard carbon layer in the homogeneous region (black thickness/white thickness) is 0.01 to 0.3.

3. The sliding member according to claim 1 or 2,

sp of the white hard carbon layer²/sp³A sp ratio of 0.2 to 0.7, the black hard carbon layer²/sp³Sp ratio smaller than the white hard carbon layer²/sp³The ratio is 0.05 to 0.3。

4. The sliding member according to any one of claims 1 to 3,

when a cross section is observed by a bright field TEM image, a hard carbon base film indicated by white is provided between the base material or a base film provided on the base material and the coating film so as to be opposed to each other.

5. The sliding member according to any one of claims 1 to 4,

when a cross section is observed by a bright field TEM image, a hard carbon surface film relatively indicated by white is provided on the coating film.

6. The sliding member according to any one of claims 1 to 5,

the sliding member is a piston ring.

7. A coating film in which repeating units comprising a black hard carbon layer represented by black and a white hard carbon layer represented by white are laminated in the thickness direction when the cross section thereof is observed by a bright field TEM image, and which has a thickness in the range of 1 to 50 [ mu ] m,

the coating film has an inclined region in which the thickness of the white hard carbon layer in the repeating unit gradually increases in the thickness direction, and a homogeneous region provided on the inclined region in which the thickness of the white hard carbon layer in the repeating unit is the same or substantially the same in the thickness direction, the inclined region has a form of V-shaped or radial growth in the thickness direction, and the homogeneous region does not have a form of V-shaped or radial growth in the thickness direction.

Technical Field

The present invention relates to a sliding member and a coating film. More specifically, the present invention relates to a sliding member having a coating film exhibiting constant and stable chipping resistance and wear resistance and excellent peeling resistance (adhesion), and to the coating film.

Background

In recent years, in various industrial fields, particularly in the automotive field, studies have been extensively conducted on a hard carbon layer as a coating film on the surface of a sliding member requiring slidability, such as an engine base material and other machine base materials. The hard carbon layer is generally referred to by various names such as a diamond-like carbon (DLC) film, an amorphous carbon layer, an i-carbon film, and a diamond-like carbon layer. Such a hard carbon layer is structurally classified as amorphous.

It is considered that a single bond as seen in diamond crystals and a double bond as seen in graphite crystals are mixedly present in the hard carbon layer. The hard carbon layer has high hardness and high wear resistance as well as excellent chemical stability, etc. like diamond crystals, and also has low hardness, high lubricity, excellent target adaptability, etc. like graphite crystals. Further, since the hard carbon layer is amorphous, it is excellent in flatness, and also has low friction (i.e., a small friction coefficient) in direct contact with a target material and excellent target adaptability.

Chipping resistance (chipping resistance) and wear resistance are important characteristics for a sliding surface of a sliding member. However, since the chipping resistance (chipping resistance) and the wear resistance are in a trade-off relationship, it is difficult to provide a coating film satisfying these characteristics. As a means for solving the problem, it has been studied to provide a hard carbon layer having a low hardness or a film in which a hard carbon having a low hardness and a hard carbon having a high hardness are mixed, thereby achieving both chipping resistance and wear resistance.

However, it is still insufficient to achieve both chipping resistance and wear resistance. In addition to chipping resistance and wear resistance, low friction properties and peeling resistance are required for a coating film provided on a sliding member to which a high load is applied, such as a piston ring, but improvement of these properties is not sufficient at present.

As for the improvement of the properties of the hard carbon layer, hard carbon layers formed by CVD methods described in patent documents 1 to 3 and hard carbon layers formed by PVD methods described in patent documents 4 and 5 have been proposed. Specifically, patent document 1 proposes a hard carbon layer having high hardness, low friction coefficient, and excellent sliding properties. The surface roughness of the hard carbon layer is less than Rmax500nm, and the ratio of diamond structure cluster with 100-2000 carbon atoms to graphite structure cluster with 100-2000 carbon atoms is 0.3-3.

Patent document 2 proposes a conductive hard carbon coating that has excellent wear resistance, oxidation resistance, and food resistance and is used in applications and processes in which conductive members are in contact with each other, or in corrosive environments, and a coating member thereof. The conductive hard carbon coating film has sp²And a structure in which at least a part of the bonded crystals are continuously connected in the film thickness direction.

Patent document 3 proposes an oriented amorphous carbon layer having a new structure and exhibiting high conductivity, and a method for forming the same. The amorphous carbon layer is an oriented amorphous carbon layer which contains C as a main component, contains N3-20 atomic%, has H of more than 0 atomic% and 20 atomic% or less, and has sp when the total amount of C is 100 atomic%²Carbon of hybrid orbital (Csp)²) Is 70 atomic% or more and less than 100 atomic%, and the (002) plane of the graphite is oriented in the thickness direction. It is also proposed that the amorphous carbon layer can be formed by a direct current plasma CVD method in which a reaction gas containing a compound selected from the group consisting of Csp and a compound having a refractive index of-1500V or less is discharged²And a gas containing Csp²And nitrogen and/or silicon, and nitrogen.

Patent document 4 discloses a DLC film as a coating film having excellent wear resistance, a low friction coefficient, and excellent sliding properties, and a member having excellent equivalent properties. The coating film is an amorphous structure mainly composed of carbon, and is a DLC hard multilayer film in which a low-hardness hard carbon layer containing graphite clusters having an average diameter of 2nm or more and a high-hardness hard carbon layer containing graphite clusters having an average diameter of 1nm or less are alternately laminated.

Patent document 5 proposes a sliding element, particularly a piston ring, comprising a metal-containing adhesive layer and a coating layer having a ta-C DLC layer with a thickness of at least 10 μm from the inside to the outside on at least 1 sliding surface.

Disclosure of Invention

Problems to be solved by the invention

The above-mentioned technique by the CVD method is not sufficient in terms of both chipping resistance and wear resistance, nor is it sufficient in terms of improvement of low friction property and peeling resistance. That is, the film forming method by the CVD method has a high film forming temperature, and uses a gas material containing hydrogen, so that hydrogen is contained in the hard carbon layer after film formation. The hard carbon layer has low hardness, excellent chipping resistance, and excellent durability because a thick film can be easily formed. However, the hard carbon layer has low hardness and thus insufficient wear resistance, and the hard carbon layer contains hydrogen, so that the hard carbon layer has lower friction in oil than the hard carbon layer formed by the PVD method.

On the other hand, in the PVD method, since the cathode uses a solid carbon material, the hydrogen content in the hard carbon layer may be 10 atomic% or less, and the hard carbon having excellent low friction property in oil may be formed into a film with high hardness without containing hydrogen or impurity metal. In the case of forming a hard carbon layer by PVD method, sp is generated when the substrate temperature is increased³Bonded carbon (diamond structure) becomes difficult to generate, and sp is generated²A low-hardness hard carbon layer rich in binding carbon (graphite structure) is formed. Therefore, conventionally, film formation has been carried out at a substrate temperature of 200 ℃ or lower, sp³The hard carbon layer has a high binding carbon ratio and excellent wear resistance.

However, when the hard carbon layer is formed by the PVD method, if the hard carbon layer is formed to have a thickness of more than 1 μm in order to ensure sufficient durability, compressive residual stress in the hard carbon layer becomes large, and the film breaks itself. Even if the self-destruction does not occur, the compressive residual stress is large and the strain is accumulated, and therefore, the chipping resistance is low. As described above, it is difficult to stably form a thick hard carbon layer by the PVD method, and it is difficult to secure sufficient durability.

A sliding member provided with a coating film having a thickness of several μm or more, such as a sliding member to which a high load is applied, particularly a piston ring, is required to have excellent adhesion between the coating film and a base material. Further, the coating film on the surface side is required to exhibit chipping resistance and wear resistance in a stable and constant state even when wear gradually progresses.

The present invention has been made to solve the above problems, and an object thereof is to provide a sliding member having a coating film exhibiting constant and stable chipping resistance and abrasion resistance and excellent peeling resistance (adhesion), and the coating film.

Means for solving the problems

The sliding member of the present invention has a coating film formed of a hard carbon layer on a sliding surface,

when a cross section of the coating film is observed by a bright field TEM image, repeating units comprising a black hard carbon layer relatively represented by black and a white hard carbon layer relatively represented by white are laminated in the thickness direction, and have a thickness in the range of 1 μm to 50 μm,

the coating film has an inclined region provided on the substrate side, in which the thickness of the white hard carbon layer in the repeating unit gradually increases in the thickness direction, and a homogeneous region provided on the surface side, in which the thickness of the white hard carbon layer in the repeating unit is the same or substantially the same in the thickness direction, the inclined region has a form of growing in a V-shape or a radial shape in the thickness direction, and the homogeneous region does not have a form of growing in a V-shape or a radial shape in the thickness direction.

The relatively white hard carbon layer has a low density, sp²/sp³Large ratio, low friction and excellent chipping resistance. Relatively black hard carbon layerIs of high density, sp²/sp³Small ratio and excellent strength. According to the present invention, since the coating film has, on the substrate side, the inclined region in which the thickness of the white hard carbon layer in the repeating unit gradually increases (becomes thicker) in the thickness direction and the thickness of the black hard carbon layer gradually decreases (becomes thinner) in the thickness direction, it is possible to strongly adhere to the substrate and improve the adhesion particularly in the inclined region in which the high-strength black hard carbon layer is present in a large amount on the substrate side. In particular, since the inclined region has a form of V-shaped or radial growth in the thickness direction, which is not observed in the homogeneous region, the V-shaped or radial structure is entangled with the black hard carbon layer, the adhesion is increased, and the peeling resistance (adhesion) can be improved. Further, since the coating film has a homogeneous region on the surface side thereof, in which the thicknesses of the white hard carbon layers in the repeating units are the same or substantially the same in the thickness direction, even when the coating film is gradually worn, the shaving resistance and the wear resistance can be exhibited in a stable and constant state due to the presence of the homogeneous region of the white hard carbon layer, which is particularly excellent in the low friction property and the shaving resistance.

In the sliding member of the present invention, the ratio of the thickness of the black hard carbon layer to the thickness of the white hard carbon layer (black thickness/white thickness) in the homogeneous region is 0.01 to 0.3. According to the present invention, since the black hard carbon layer is laminated as a film rich in the white hard carbon layer with the thickness ratio of the black hard carbon layer being within the above range in the homogeneous region, even when the wear of the coating film progresses, the chipping resistance and the wear resistance are constant and stable.

In the sliding member of the present invention, sp of the white hard carbon layer²/sp³Sp ratio of the black hard carbon layer of 0.2 to 0.7²/sp³Sp ratio smaller than the above white hard carbon layer²/sp³And the ratio is 0.05 to 0.3. According to the present invention, the hard carbon layer has sp within the above range between the white hard carbon layer having a low density and excellent chipping resistance and the black hard carbon layer having a high density and high strength²/sp³In contrast, the inclined region and the homogeneity are formed by the white hard carbon layer and the black hard carbon layerTherefore, the resin composition shows constant and stable chipping resistance and abrasion resistance, and is excellent in peeling resistance (adhesion).

In the sliding member of the present invention, when a cross section is observed by a bright field TEM image, a hard carbon base film indicated by white is provided between the base material or a base film provided on the base material and the coating film.

In the sliding member according to the present invention, when a cross section is observed by a bright field TEM image, a hard carbon surface film relatively indicated by white is provided on the coating film.

In the sliding member according to the present invention, the sliding member is preferably a piston ring.

The coating film of the present invention is characterized in that when a cross section is observed by a bright field TEM image, repeating units including a black hard carbon layer represented by black and a white hard carbon layer represented by white are laminated in a thickness direction, and have a thickness in a range of 1 to 50 [ mu ] m,

the coating film has an inclined region in which the thickness of the white hard carbon layer in the repeating unit gradually increases in the thickness direction, and a homogeneous region provided on the inclined region in which the thickness of the white hard carbon layer in the repeating unit is the same or substantially the same in the thickness direction, the inclined region has a form of growing in a V-shape or a radial shape in the thickness direction, and the homogeneous region does not have a form of growing in a V-shape or a radial shape in the thickness direction.

According to the present invention, as described above, since the hard white carbon layer in the repeating unit has the inclined region in which the thickness thereof gradually increases (becomes thicker) in the thickness direction, the existence of the inclined region can strongly adhere to the base material of the sliding member, thereby improving the adhesion. In particular, since the inclined region has a form of V-shaped or radial growth in the thickness direction, which cannot be observed in the homogeneous region, the V-shaped or radial structure is entangled with the black hard carbon layer, the adhesion is increased, and the peeling resistance (adhesion) can be improved. In addition, since the inclined region has a homogeneous region in which the thicknesses of the white hard carbon layers in the repeating units are the same or substantially the same in the thickness direction, even when the wear of the coating film gradually progresses, the chipping resistance and the wear resistance can be exhibited in a stable and constant state due to the presence of the homogeneous region. Such a coating film can be suitably used for a coating film having a thickness of, for example, several μm or more, particularly, a sliding member to which a high load is applied, such as a piston ring.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a sliding member having a coating film which exhibits constant and stable chipping resistance and wear resistance and is excellent in peeling resistance (adhesion), and the coating film can be used as a sliding member and a coating film to which a high load is applied, particularly a piston ring or the like.

Drawings

Fig. 1 is a schematic cross-sectional view showing an example of a coating film provided on a sliding member of the present invention.

Fig. 2 is an explanatory view of an inclined region and a homogeneous region constituting the clad layer.

Fig. 3 is a bright field TEM image showing a cross section of an example of the clad film.

Fig. 4 is a bright field TEM image of the tilted area.

Fig. 5 is a schematic cross-sectional view showing an example of a piston ring having a coating film.

Fig. 6 is a graph showing changes in the substrate temperature during the formation of the hard carbon layer.

Fig. 7 is a schematic diagram of a frictional wear test method using an SRV tester.

Fig. 8 is a photomicrograph showing the results of the frictional wear test of example 1.

Description of the symbols

1 coating film

2 inclined area

3 homogeneous region

11 base material (piston ring base material)

11a base layer

12 intermediate layer

16 sliding surface

20 frictional wear test specimen

21 sliding object

120 SRV testing machine

B black hard carbon layer

W white hard carbon layer

Y thickness direction

Detailed Description

The coating film and the piston ring of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following description and drawings, and includes modifications within the spirit and scope thereof.

[ coating film ]

For example, as shown in an example of a piston ring in fig. 5, a sliding member 10 of the present invention has a coating film 1 formed of a hard carbon layer on a sliding surface 16. as shown in fig. 1 to 3, when a cross section of the coating film 1 is observed by a bright field TEM image, a repeating unit (indicated by reference numeral ＊ in fig. 2) including a black hard carbon layer B indicated by black and a white hard carbon layer W indicated by white is laminated in a thickness direction Y and has a thickness in a range of 1 μm to 50 μm. the coating film 1 has an inclined region 2 provided on a substrate side and a homogeneous region 3 provided on a surface side, the thickness of the white hard carbon layer W in the repeating unit is gradually increased in the thickness direction Y in the inclined region 2 (may also be referred to as "thickened". the same as in the present application), and the thickness of the white hard carbon layer W in the repeating unit is the same or substantially the same in the thickness direction Y in the homogeneous region 3, and the inclined region 2 has a form of V-shaped or radial type growth in the thickness direction Y-shaped homogeneous region 3.

In the sliding member 10, the hard carbon layer W having a relatively white color has a low density sp²/sp³Large specific gravity, low friction and excellent chipping resistance, and the black hard carbon layer B has high density sp²/sp³Small ratio and excellent strength. According to the sliding member 10, since the coating film 1 has the inclined region 2 on the substrate side, the thickness of the white hard carbon layer W in the repeating unit is increased in the inclined region 2Since the degree of hardness gradually increases in the thickness direction Y and the thickness of the black hard carbon layer B gradually decreases in the thickness direction Y, particularly, the black hard carbon layer B having high strength is present in a large amount in the inclined region 2 on the substrate side, and thus strong adhesion to the substrate can be achieved, and adhesion can be improved. In particular, since the inclined region 2 has a V-shaped or radial growth form in the thickness direction Y, which cannot be observed in the homogeneous region 3, a V-shaped or radial structure is entangled with the black hard carbon layer B, so that the adhesion is high, and the peeling resistance (adhesion) can be improved. Further, since the homogeneous region 3 is provided on the surface side of the coating film 1, and the thicknesses of the white hard carbon layers W in the repeating units are the same or substantially the same in the thickness direction Y in the homogeneous region 3, the shaving resistance and the wear resistance can be exhibited in a stable and constant state even when the coating film 1 is gradually worn due to the presence of the homogeneous region 3 of the white hard carbon layer W having excellent friction properties and shaving resistance in particular. Thus, the sliding member 10 having the coating film 1 exhibiting constant and stable chipping resistance and wear resistance and excellent peeling resistance (adhesion) is obtained.

The bright field TEM image can be obtained by observing the coating film 1 formed into a thin film by using fib (focused Ion beam) at an acceleration voltage of 300kV by TEM (transmission electron Microscope). The thickness direction Y is a direction in which the coating films 1 are sequentially stacked on the substrate 11.

Hereinafter, the components of the sliding member will be described in detail. In the following description, a piston ring is given as an example of a sliding member in many cases, but the sliding member of the present invention is not limited to the piston ring.

(substrate)

As shown in fig. 1 and 2, the substrate 11 is a target member on which the coating film 1 is provided. The substrate 11 is not particularly limited, and examples thereof include iron-based metals, nonferrous metals, ceramics, and hard composite materials. Examples thereof include: carbon steel, alloy steel, hardened steel, high speed tool steel, cast iron, aluminum alloy, magnesium alloy, super hard alloy, and the like. Considering the film formation temperature of the coating film 1, a substrate whose characteristics do not significantly deteriorate at a temperature exceeding 200 ℃ is preferable.

When the coating film 1 is applied to the piston ring 10, the piston ring base material 11 may be made of various materials that can be used as a base material of the piston ring 10, and is not particularly limited. For example, various steel materials, stainless steel materials, casting materials, cast steel materials, and the like can be applied. Among these, martensitic stainless steel, chromium manganese steel (SUP9 material), chromium vanadium steel (SUP10 material), silicon chromium steel (SWOSC-V material), and the like are exemplified. The substrate 11 may have a base layer 11a shown in fig. 1 as needed. The base layer 11a is not particularly limited, and may be made of a material that improves adhesion to the intermediate layer 12, which will be described later.

The piston ring base material 11 may be provided with at least 1 nitride, carbonitride, carbide, or the like layer of Cr, Ti, Si, Al, or the like as the underlying layer 11 a. Examples of such a compound layer include CrN, TiN, CrAlN, TiC, TiCN, TiAlSiN, and the like. Among these, a nitride layer (not shown), a Cr-N type, Cr-B-N type, Ti-N type or other wear-resistant coating (not shown) formed by nitriding treatment is preferable. Among them, it is preferable to form a wear-resistant coating such as Cr-N type, Cr-B-N type, Ti-N type, etc. Since the piston ring 10 exhibits excellent wear resistance without providing such nitriding treatment or Cr-based or Ti-based wear-resistant coating, the nitriding treatment or the formation of Cr-based or Ti-based wear-resistant coating is not an essential configuration.

The piston ring base material 11 may be pretreated as necessary. As the pretreatment, surface polishing is preferably performed to adjust the surface roughness. The adjustment of the surface roughness is preferably performed by, for example, a method of polishing the surface of the piston ring base material 11 with a diamond abrasive to perform surface grinding. Such a piston ring base material 11 can be preferably applied as a pretreatment before forming an intermediate layer 12 or the like described later, or a pretreatment before forming a foundation layer 11a or the like provided in advance before forming the intermediate layer 12 or the like.

(intermediate layer)

As shown in fig. 1 and 2, an intermediate layer 12 is preferably provided between the base material 11 and the cover film 1 as needed. The intermediate layer 12 can further improve the adhesion between the base material 11 and the coating film 1, and can allow the exposed intermediate layer 12 to exhibit an abrasion resistance function when the coating film 1 is abraded.

The intermediate layer 12 may be a layer containing at least 1 or 2 or more of elements such as Cr, Ti, Si, W, and B. The underlayer 11a formed of a compound such as a nitride, carbonitride, carbide, or the like containing at least 1 or 2 or more elements of Cr, Ti, Si, Al, or the like may be provided in the lower layer of the intermediate layer 12 (between the base material 11 and the intermediate layer 12). Examples of such compounds include: CrN, TiN, CrAlN, TiC, TiCN, TiAlSiN and the like. The formation of the base layer 11a provided with the intermediate layer 12 as necessary can be performed as follows: for example, the substrate 11 is placed in a chamber, the chamber is evacuated, then, an inert gas is introduced by preheating, ion cleaning, or the like, and the process is performed by a method such as vacuum deposition or ion plating.

When the coating film 1 is applied to the piston ring 10, the intermediate layer 12 may be a titanium film, a chromium film, or the like. The intermediate layer 12 in this case is not necessarily provided, and the formation thereof is arbitrary. The intermediate layer 12 such as a titanium film or a chromium film can be formed by various film forming methods such as a vacuum deposition method, a sputtering method, and an ion plating method. For example, the piston ring base material 11 may be installed in a chamber, the chamber may be evacuated, and then, the chamber may be preheated, ion-cleaned, or the like, and an inert gas may be introduced. The thickness of the intermediate layer 12 is not particularly limited, but is preferably in the range of 0.05 μm to 2 μm. The intermediate layer 12 is preferably formed at least on an outer peripheral sliding surface 16 on which the piston ring 10 slides in contact with a cylinder liner (not shown), but may be formed on other surfaces, for example, an upper surface, a lower surface, and an inner peripheral surface of the piston ring 10.

The intermediate layer 12 may be formed directly on the piston ring base material 11, or may be formed on the surface after the nitriding treatment, i.e., on the underlying layer 11a including the wear-resistant coating film. The intermediate layer 12 improves the adhesion between the piston ring base material 11 and the coating film 1. If necessary, another layer may be provided between the intermediate layer 12 and the cover film 1 for the purpose of improving the adhesion therebetween. For example, a film having the same or substantially the same composition as that of the coating film 1 described later may be formed.

(coating film)

As shown in fig. 2 to 4, when bright field TEM images of the cross section of the coating film 1 are observed, 2 hard carbon layers (W, B) are provided, which are indicated by 2 colors of white and black. The white hard carbon layers W and the black hard carbon layers B are alternately laminated. The coating film 1 has an inclined region 2 provided on the substrate side and a homogeneous region 3 provided on the front side, and the thickness of the white hard carbon layer W in the repeating unit is gradually increased in the thickness direction Y in the inclined region 2, and the thickness of the white hard carbon layer W in the repeating unit is the same or substantially the same in the thickness direction Y in the homogeneous region 3.

When the coating film 1 is applied to the piston ring 10, as shown in fig. 5, the coating film 1 is formed on at least an outer peripheral sliding surface 16 on which the piston ring 10 slides in contact with a cylinder liner (not shown). The surface may be formed on any other surface, for example, the upper surface, the lower surface, or the inner circumferential surface of the piston ring 10.

Sp of relatively white hard carbon layer W²/sp³The ratio is large. sp²/sp³The ratio is preferably 0.2 to 0.7, and more preferably 0.3 to 0.6. The hard carbon layer W appeared relatively white due to sp²/sp³The ratio is large. By setting sp to this range²/sp³In contrast, the density can be low and the friction and chip resistance are excellent. In this specification, sp is²And sp³The measurement can be carried out by a Transmission Electron Microscope (TEM) combined with Electron Energy Loss Spectroscopy (EELS). The black hard carbon layer B can be measured in the same manner. The low density means that the density is relatively low compared to the density of the black hard carbon layer B, which is relatively black.

The hard carbon layer B which is relatively black is less than sp of the hard carbon layer B which is white²/sp³The ratio is 0.05 to 0.3, preferably 0.1 to 0.25. The hard carbon layer B appeared relatively black due to sp²/sp³The ratio is large. By setting sp to this range²/sp³In this case, the density can be high and the strength is excellent. The high density means that the density is relatively high compared to the density of the white hard carbon layer W which is relatively white.

The inclined region 2 is sp having the above range in the repeating unit²/sp³The thickness of the white hard carbon layer W is gradually increased in the thickness direction Y of the cover film 1, and sp within the above range²/sp³The black hard carbon layer B is smaller in the thickness direction Y of the cover film 1. For example, as shown in fig. 4, when the hard carbon layer initially provided on the intermediate layer 12 has a repeating unit thickness of 1, a white hard carbon layer W having a thickness of about 0.3 is provided on a black hard carbon layer B having a thickness of about 0.7. The repeating unit thereon was provided with a white hard carbon layer W having a thickness of about 0.6 on a black hard carbon layer B having a thickness of about 0.4. Further, the above repeating unit was provided with a white hard carbon layer W having a thickness of about 0.8 on the black hard carbon layer B having a thickness of about 0.2. Thus, the ratio of the thicknesses of the black hard carbon layer B and the white hard carbon layer W in the inclined region 2 changes in the thickness direction Y of the cover film 1, and the ratio of the thicknesses of the black hard carbon layer B gradually decreases and the ratio of the thicknesses of the white hard carbon layer W gradually increases as the repeating units are stacked. In such a gradient region 2, since a large amount of the high-strength black hard carbon layer B is present on the substrate side in particular, adhesion to the substrate 11 (these layers in the case where the base layer 11a and the intermediate layer 12 are provided) can be improved.

In the inclined region 2, the boundary between the white hard carbon layer W and the black hard carbon layer B in each repeating unit is not parallel to the flat surface of the cover film 1 or the substrate 11, but is wavy or triangular wavy. The reason for this is that when the hard carbon layer of the repeating unit is formed, the growth rate of the black hard carbon layer B formed first is different over the entire surface, and the black hard carbon layer B is likely to grow in a wavy or triangular wavy form. As a result, the boundary between the black hard carbon layer B and the white hard carbon layer W is considered to have a wavy shape or a triangular wavy shape as shown in fig. 2 to 4.

In the inclined region 2, the white hard carbon layer W may have a mesh-like, scaly, dendritic or lamellar and shapeable three-dimensional growth form. In such a growth form, the white hard carbon layer W may contain black hard carbon. The white hard carbon layer W has a triangular wave-like form (a form in which the layer gradually expands from the position of the fan rib (fan axis)) or a radial form with respect to the film growth direction.

When a bright field TEM image of the cross section of the laminated film is observed by a bright field TEM at an acceleration voltage of 200 to 300kV, which is a commonly used condition, in the inclined region 2, the white hard carbon layer W grows in a V-shape or a radial shape on the black hard carbon layer B in the thickness direction Y of the laminated film. The V-shaped or radial structure is entangled with the black hard carbon layer B, and the adhesion is increased. Such morphological structure is hardly observed in the homogeneous region 3 provided on the front surface side.

The homogeneous region 3 is sp having the above range in the repeating unit²/sp³A thickness of the white hard carbon layer W in proportion to sp having the above range²/sp³The thickness of the black hard carbon layer B is the same or substantially the same in the thickness direction Y of the cover film 1. For example, as shown in fig. 3, when the thickness of the repeating unit is 1, the white hard carbon layer W having a thickness of about 0.9 is provided on the black hard carbon layer B having a thickness of about 0.1 for any repeating unit among the repeating units provided on the inclined region 2. Thus, the ratio of the thicknesses of the black hard carbon layer B and the white hard carbon layer W in the homogeneous region 3 is the same or substantially the same in the thickness direction Y of the cover film 1. In such a homogeneous region 3, particularly, since the white hard carbon layer W excellent in low friction property and chipping resistance is present in the same manner in each repeating unit, even when the wear of the coating film 1 gradually progresses, chipping resistance and wear resistance can be exhibited in a stable and constant state.

In the homogeneous region 3, the ratio of the thicknesses of the black hard carbon layer B and the white hard carbon layer W (black thickness/white thickness) is substantially constant, and is preferably in the range of 0.01 to 0.3 in terms of chipping resistance and wear resistance. In the homogeneous region 3, the black hard carbon layer B has a small thickness ratio within the above range, and is stacked as a film rich in the white hard carbon layer W.

In the homogeneous region 3, the boundary between the white hard carbon layer W and the black hard carbon layer B in each repeating unit is a relatively parallel and flat surface with respect to the surface of the coating film 1 or the substrate 11, and the wavy or triangular wavy shape of the inclined region 2 is not conspicuous. The reason for this is considered that, unlike the case of the inclined region 2, the thickness of the black hard carbon layer B formed first is small, and therefore, the white hard carbon layer W starts to be formed before growing in a wavy or triangular wavy manner.

In the homogeneous region 3, as shown in fig. 2 and 3, the black hard carbon layer B has a smaller proportion than the white hard carbon layer W, and when a cross section is observed by a bright field TEM image, the black hard carbon layer B may not be observed in the in-plane direction (width direction) at a constant or substantially constant thickness. However, the black hard carbon layer B was intermittently observed in the in-plane direction to at least the extent that the repeating units could be distinguished.

The ratio of the homogeneous region 3 to the total thickness of the laminated film ("thickness of the homogeneous region 3 + thickness of the inclined region 2") is preferably 0.5 to 0.9. By making the homogeneous region 3 occupy most of the thickness of the entire laminated film, even when the wear of the clad film 1 gradually progresses, the shaving resistance and the wear resistance can be exhibited in a stable and constant state by the homogeneous region 3. The inclined region 2 can strongly adhere the homogeneous region 3 having stable characteristics to the base material (which may include the base layer 11a and the intermediate layer 12), thereby improving adhesion. As a result, the peeling resistance (adhesion) of the inclined region 2, which exhibits constant and stable chipping resistance and wear resistance, can be made excellent. Such characteristics are desired for a sliding member and a coating film, particularly for a piston ring or the like, and a sliding member exhibiting constant and stable chipping resistance and wear resistance and excellent peeling resistance (adhesion) can be produced as compared with a sliding member not having the characteristics of the present invention.

The clad film 1 may be formed larger thanA thickness within a range of 1 μm to 50 μm. The formation of the coating film 1 having a thickness in the above range in which the white hard carbon layer W and the black hard carbon layer B are laminated can be achieved by the following method: as a film formation temperature (substrate temperature) in the PVD method, a film formation at 200 ℃ or lower and a film formation at more than 200 ℃ are alternately performed. When the film is formed at a temperature exceeding 200 ℃, it becomes sp²/sp³A slightly larger white hard carbon layer W. On the other hand, when the film is formed at 200 ℃ or lower, it becomes sp²/sp³A small black hard carbon layer B. The cover film 1 can be formed into a thick film in the above range by alternately laminating these films. As a result, the coating film 1 exhibiting constant and stable chipping resistance and abrasion resistance and excellent peeling resistance (adhesion) can be formed.

The thickness of each repeating unit of the hard carbon layer (the thickness of the laminated film 1 layer) is preferably in the range of 0.1 to 4 μm. In the repeating unit, the thicknesses of the black hard carbon layer B and the white hard carbon layer W in the inclined region 2 are changed in an inclined manner within the above-described range, and the thicknesses of the black hard carbon layer B and the white hard carbon layer W in the homogeneous region 3 are constant or substantially constant within the above-described range. The thickness is more preferably in the range of 0.3 to 1 μm.

The obtained coating film 1 is an amorphous carbon layer or an amorphous carbon layer partially containing graphite, and has a low friction coefficient against a target material and good abrasion resistance against the target material.

As shown in fig. 3, the cover film 1 may have a raised shape extending over at least 2 or more stacked layers. The raised shape is a portion that looks like a raised formation, and is a portion that looks like a particle or a balloon. The layered state in the case where the raised shape is present is not similarly layered so as to be aligned in the thickness direction Y, but is easily expressed mainly in the upper half portion, and appears to be disordered, but does not greatly affect the properties such as wear resistance and chipping resistance. The mechanism of formation of the ridge shape is not yet clarified, but it is considered that large particles probably form a starting point in film formation.

The hard carbon layer constituting the coating film 1 contains hydrogen in the range of 0.1 atomic% or more and 10 atomic% or less, preferably 8 atomic% or less, of any of the white hard carbon layer W and the black hard carbon layer B, excluding carbon. The hydrogen content can be determined by hfs (hydrogen Forward scattering) analysis, the remainder consisting essentially of carbon only, and preferably not containing elements other than N, B, Si and other unavoidable impurities. Even if these elements are contained in the white hard carbon layer W, the chipping resistance can be improved. On the other hand, in the black hard carbon layer B, if the remaining portion is substantially composed of only carbon, hardness is increased, and abrasion resistance is improved, which is preferable. "consisting essentially of only carbon" means that the element other than N, B, Si and other unavoidable impurities is not contained.

(film formation of coating film)

The coating film 1 can be formed by a PVD method such as an arc PVD method or a sputtering PVD method. Among these, it is preferable to use a carbon target and form the film by arc ion plating in which hydrogen atoms are not contained in the film forming raw material.

When the coating film 1 is formed by the arc ion plating method, it is preferable to adjust a bias voltage and an arc current, heat the substrate by a heater, introduce a cooling device into a jig (holder) for fixing the substrate, and forcibly cool the substrate. For example, as shown in FIG. 6, sp is measured by controlling the temperature of the substrate and the pressure in the furnace, for example²/sp³The coating film 1 in which different hard carbon layers (white hard carbon layer W and black hard carbon layer B) are alternately laminated is formed.

To sp²/sp³The black hard carbon layer B is formed at a ratio of 0.05 to 0.3, and is formed at a substrate temperature of more than 50 ℃ and not more than 200 ℃. In order to alternately laminate the black hard carbon layer B and the white hard carbon layer W, the following method may be employed: after the white hard carbon layer W is formed, a cooling step is performed, the substrate temperature is lowered to 200 ℃ or lower, and then the black hard carbon layer B is formed.

To sp²/sp³Forming a white hard carbon layer W with a ratio of 0.2-0.7, and controlling the substrate temperature to be more than 200 DEGAt 300 ℃ or lower, more preferably 220 to 275 ℃. The substrate temperature is preferably controlled by controlling the bias voltage to-50V to-400V, but the substrate temperature can be controlled by changing the arc current, heating by a heater, and cooling by a jig. Therefore, the control is not particularly limited to the bias control.

The substrate temperature may be adjusted by adjusting an arc current, a heater temperature, a furnace pressure, or the like in addition to the bias voltage, and therefore, the bias voltage is not particularly limited. However, it is considered that if it exceeds-50V, it becomes difficult to form a mesh-like hard carbon layer, and on the other hand, if it is less than-400V, it becomes difficult to form a mesh-like hard carbon layer, and it is preferably-50 to-400V. Further, the pressure in the furnace was set to 10^-4～5×10^-1In the case of a vacuum atmosphere of Pa, a hard carbon layer having low friction and high abrasion resistance can be obtained as compared with the case of introducing hydrogen gas or nitrogen gas, and therefore, this is preferable.

(sp²/sp³Than)

The hard carbon layer is a carbon bond sp represented by graphite²Bond and carbon bond sp represented by diamond³A membrane in which bonds are present in mixture. Here, 1s → π is determined by EELS analysis (Electron Energy-Loss Spectroscopy)^＊Intensity sum 1s → σ^＊Intensity, 1s → pi^＊Intensity as sp²Intensity, 1s → σ^＊Intensity as sp³Intensity, the ratio of which is 1s → π^＊Intensity sum 1s → σ^＊Ratio of intensities as sp²/sp³And (4) the ratio. Thus, sp as described in the present invention²/sp³The ratio refers precisely to the pi/sigma intensity ratio. Specifically, a spectral imaging method in STEM (scanning TEM) mode is applied, and the sample absorption current is 10 at an acceleration voltage of 200kv^-9A. EELS obtained at a 1nm pitch under a beam spot size of 1nm were integrated, and a C-K absorption spectrum was extracted as average information from a region of about 10nm to calculate sp²/sp³And (4) the ratio.