JP2006250348A - Sliding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sliding member having an amorphous hard carbon film having hydrogen content of 5 at% or less and superior in adhesiveness with a base material and abrasion resistance, with high hardness. <P>SOLUTION: This sliding member has the base material, an intermediate layer formed on a surface of the base material, and the amorphous hard carbon film having hydrogen content of 5 at% or less, formed on a surface of the intermediate layer and including carbon as its main component. Oxygen concentration of the intermediate layer is increased from a surface side toward the inside of intermediate layer, and carbon concentration is decreased from the surface side toward the inside of intermediate layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sliding member in which an amorphous hard carbon film is coated on the surface of a sliding portion used under severe sliding conditions such as automobile parts.

An amorphous hard carbon film containing a relatively large number of carbon atoms in the same bonding state as diamond is generally called diamond-like carbon (DLC), and it is known that the properties of the film differ depending on the raw material used and the film formation method. ing.
1) A DLC film formed by a CVD method (plasma CVD method or the like) using a hydrocarbon gas such as methane or acetylene as a raw material contains about 30 to 40 at% hydrogen in the film, and the film hardness is The Vickers hardness is about Hv 1000 to 2000.
2) The DLC film formed by PVD method (sputtering method, vacuum arc deposition method, etc.) using graphite as a raw material has a hydrogen content of 5 at% or less, and the film hardness should be Hv 3000 or more in terms of Vickers hardness. It has a high hardness and very excellent wear resistance as compared with the film of 1). This is probably because the film according to 2) has a higher proportion of sp3 type bonds (diamond structure bonds) than the film with a high hydrogen content according to 1).

As described above, since the DLC film has a feature of a low friction coefficient and excellent wear resistance, application to a sliding member has been attempted. In recent years, the DLC film has been applied to surface treatments such as molds and tools. However, the application of DLC coatings to sliding members used in harsh sliding environments such as automobile parts has not progressed much.
This is because it is difficult to ensure the adhesion of the DLC film to the substrate. In general, cemented carbide is often used as a base material for molds and tools. This cemented carbide is a composite alloy composed of a stable carbide such as tungsten carbide and cobalt and has a high hardness, so that a DLC film can be coated on the surface with good adhesion. On the other hand, most of general machine parts and automobile parts use iron-based materials, and the adhesion of the DLC film to these iron-based materials is not sufficient, and there is a problem that the film peels off during use of the sliding member. is there.

Then, the technique of forming an intermediate | middle layer between a DLC film and a base material is disclosed as a method of improving the adhesiveness of a DLC film and the base material which consists of iron-type materials. For example, a technique is disclosed in which the intermediate layer is composed of a plurality of metal layers, and the outermost intermediate layer is an amorphous layer of metal and carbon, thereby improving the adhesion to the DLC film (patent) Reference 1). In this technique, a gradient composition in which the carbon concentration of the amorphous layer is increased from the substrate side toward the surface side can be obtained. In addition, a technique of providing a carbide layer of a metal such as Ti, Cr, Si as an intermediate layer is disclosed (see Patent Document 2).
Furthermore, a technique for forming a mixed layer of carbon atoms and implanted atoms between the DLC film and the substrate is disclosed (see Patent Document 3). This mixed layer is formed by injecting nitrogen ions or the like after forming a DLC film on the substrate.

JP2003-171758 (paragraphs 0025 and 0027) Japanese Patent Laid-Open No. 2001-316800 Japanese Unexamined Patent Publication No. 7-90553

However, even if the above-described conventional technique is used, the adhesion between the substrate and the DLC film is not sufficient. The reason for this is thought to be that an oxide film is easily formed on the surface of the iron-based metal substrate, and this oxide film reduces the adhesion of the DLC film. Although it is desirable to remove the oxide film in advance before forming the DLC film, it is actually difficult to completely remove the oxide film.
In particular, since the DLC film formed by the PVD method of 1) is thin and the film hardness is high, the surface pressure applied during sliding is transmitted as it is to the interface with the base material, so that peeling is more likely to occur. Therefore, when the coating according to the above 1) is used under severe sliding conditions such as automobile parts, especially when it is used for a sliding member whose sliding direction changes, such as an internal combustion engine or a valve operating system component, It was difficult to ensure the adhesion.
Accordingly, an object of the present invention is to provide a sliding member having an amorphous hard carbon film having a hydrogen content of 5 at% or less, which has excellent adhesion to a substrate, high hardness and excellent wear resistance. is there.

In order to solve the above problems, the present inventors can reduce the oxygen concentration on the surface of the intermediate layer and improve the adhesion to the DLC film by forming a large amount of oxide near the interface between the base material and the intermediate layer. Focused on.
That is, the sliding member of the present invention includes a base material, an intermediate layer formed on the surface of the base material, and an amorphous hard carbon formed on the surface of the intermediate layer and mainly containing carbon and having a hydrogen content of 5 at% or less. The intermediate layer has an oxygen concentration that increases from the surface side toward the inside of the intermediate layer, and a carbon concentration that decreases from the surface side toward the inside of the intermediate layer.

The amorphous hard carbon film preferably has a Young's modulus of 60 GPa or more, and the intermediate layer and the amorphous hard carbon film are preferably formed by a vacuum arc deposition method.
The intermediate layer is preferably composed of a metal layer having a standard free energy of formation of oxide at 100 ° C. of −600 kJ or less, and the intermediate layer includes one or more selected from the group consisting of Si, Ti, and Cr. It is preferable to consist of a metal layer containing.

  According to the present invention, it is possible to obtain a sliding member having an amorphous hard carbon film having a hydrogen content of 5 at% or less, which has excellent adhesion to a substrate, high hardness and excellent wear resistance. For this reason, for example, valve lifters and shims that are valve parts of internal combustion engines such as automobiles, piston rings and compressors that are parts of internal combustion engines, and vanes for hydraulic pumps, etc. are used under high surface pressure and require durability. The present invention can be suitably applied to the sliding member.

A preferred embodiment of the present invention will be described.
FIG. 1 is a schematic view showing a cross section of a sliding member according to an embodiment of the present invention. An intermediate layer 2 is formed on the surface of the substrate 1, and an amorphous hard carbon film (DLC film) 3 is formed on the surface of the intermediate layer 2.

<Base material>
Although the base material of the sliding member of the present invention is not particularly limited, for example, various metals and alloys can be used. In particular, the present invention is more effective when an iron-based material on which an oxide film is easily formed is used as a substrate as described later. As the iron-based material, for example, steel, stainless steel, various alloy steels, and the like can be used. For example, ferrous materials such as SKD11, SKH51, and SUJ-2 can be used in addition to carburized materials such as SCM415 according to JIS standards.

<Intermediate layer>
The intermediate layer is formed between the substrate and the amorphous hard carbon film.
(Oxygen concentration in the intermediate layer)
When various metals and alloys are used as the substrate (especially when an iron-based material is used), the surface is oxidized and an oxide film is formed when the substrate is left in the atmosphere. Since this oxide film lowers the adhesion of the DLC film, it is desirable to remove the oxide film in advance before forming the DLC film, but it is actually difficult to completely remove the oxide film. .
Therefore, the oxygen concentration of the intermediate layer surface is increased by increasing the oxygen concentration of the intermediate layer from the surface side (DLC film side) toward the inside of the intermediate layer and forming a large amount of oxide near the interface between the base material and the intermediate layer. It can reduce and can improve adhesiveness with a DLC film. That is, in this way, the oxide derived from the oxide film on the surface of the base material is fixed near the interface between the base material and the intermediate layer, so that the oxygen concentration on the surface of the intermediate layer is reduced.

The oxygen concentration on the surface of the intermediate layer is preferably 5 at% or less. The oxygen concentration on the surface of the intermediate layer can be measured from a depth profile by Auger analysis or SIMS (secondary ion mass spectrometry).
In addition, it is preferable to set it as the gradient composition which changed the oxygen concentration of the intermediate | middle layer stepwise or continuously in the layer direction. In this way, the film characteristics of the intermediate layer do not change suddenly, and peeling due to stress concentration is prevented.

(Intermediate carbon concentration)
Further, the carbon concentration of the intermediate layer is decreased from the surface side (DLC film side) toward the inside of the intermediate layer. In this case, the carbon concentration on the surface side of the intermediate layer is preferably maintained at 1 × 10 ¹⁷ atoms / cm ³ to 1 × 10 ²⁰ atoms / cm ³ to increase the affinity between the DLC film and the intermediate layer, Adhesion can be improved. Further, since a carbide or amorphous carbon layer is formed on the surface of the intermediate layer, the surface hardness is increased. Therefore, the difference in hardness from the high-hardness DLC film formed on the surface of the intermediate layer is reduced, which contributes to improving the adhesion between them.
As a method for controlling the carbon concentration in the intermediate layer, for example, carbon ions can be irradiated (ion implantation) from the surface side of the intermediate layer toward the inside after the intermediate layer is formed. Thereby, carbon ions enter the inside from the surface of the intermediate layer, and a portion having a high carbon concentration is formed in the vicinity of the surface of the intermediate layer.

  The distribution of oxygen concentration and carbon concentration in the intermediate layer can be measured by SIMS (secondary ion mass spectrometry) method or the like.

(Formation of intermediate layer)

An intermediate | middle layer can be formed from the layer of various metals or an alloy, for example. In particular, in order to form a stable oxide by reacting with the oxide layer on the surface of the base material, a layer made of a metal having a standard free energy of formation (G) of oxide of −600 kJ or less at 100 ° C. is used as the intermediate layer. It is preferable to use a layer composed of one or more components selected from the group consisting of Si, Ti, and Cr. Since such a metal or element easily forms an oxide, a stable oxide can be formed at the interface with the substrate, and oxygen can be immobilized in the vicinity of the substrate surface.
The intermediate layer can be formed using a known method such as a vacuum deposition method, a sputter deposition method, a vacuum arc deposition method, an ion plating method, and various CVD methods. Among these, it is preferable to use an ion plating method and a sputter deposition method. Particularly, when a vacuum arc deposition method is used, the ionization rate of the raw material is high, and the intermediate layer and the substrate It is most preferable because the adhesion between the two is improved.

The thickness of the intermediate layer can be set to, for example, 5 nm to 300 nm.
Moreover, it is preferable that the density of an intermediate | middle layer metal is smaller than the density of a base material. For example, in the case of an iron-based base material, the density of iron is 7.86. However, if a material having a lower density is used as the intermediate layer material, it becomes easier to obtain an implantation effect due to carbon ion irradiation, which will be described later. It becomes easy to raise the carbon concentration of.

There are the following methods for increasing the oxygen concentration of the intermediate layer from the surface side toward the inside of the intermediate layer. For example, when sputter deposition or vacuum arc deposition is used to form the intermediate layer, the final vacuum in the vacuum chamber in which the substrate is installed is reduced to a low vacuum before the intermediate layer is formed, and the residual moisture is increased. Makes it easier to oxidize. Thereby, the oxygen concentration at the interface between the substrate and the intermediate layer can be increased. At this time, oxygen present at the interface between the base material and the intermediate layer reacts with components of the intermediate layer (metal or the like) to form a stable oxide. Thereafter, as the intermediate layer is formed, oxygen in the vacuum chamber is consumed, and the oxygen concentration in the intermediate layer decreases.
Further, by setting the pressure of the atmospheric gas (Ar gas or the like) during the cleaning process of the base material before forming the intermediate layer to be low, it is possible to make the influence of residual moisture noticeable. Furthermore, the oxygen concentration can also be controlled by adjusting the pressure of the atmospheric gas in the vacuum chamber and the power applied to the cathode when forming the intermediate layer.

  By defining the distribution of oxygen concentration and carbon concentration in the intermediate layer as described above, first, oxygen on the surface of the base material reacts with the intermediate layer to form an oxide, and therefore the adhesion between the base material and the intermediate layer. Will improve. Secondly, oxygen on the surface of the substrate is fixed at the interface with the intermediate layer, and since there is little oxide on the surface of the intermediate layer, the adhesion between the intermediate layer and the DLC film is improved. Third, since a carbide or amorphous carbon layer having a high affinity with the DLC film is formed on the surface of the intermediate layer, the adhesion between the intermediate layer and the DLC film is further improved.

<Amorphous hard carbon film (DLC film)>
The DLC film is formed on the surface of the intermediate layer, and the hydrogen content is 5 at% or less. The hydrogen content of the DLC film is preferably 2 at% or less. The DLC film is preferably formed by the PVD method, more preferably by the vacuum arc deposition method. Since the DLC film formed by the CVD method has a hydrogen content exceeding 5 at%, the hardness may be low and the wear resistance may be insufficient.
It is possible to form a DLC film having a hydrogen content of 5 at% or less by a sputtering method (sputter deposition method). However, since this method has a lower ionization rate and lower carbon ion irradiation efficiency than the vacuum arc vapor deposition method, it is preferable to use a vacuum arc vapor deposition method with a high ionization rate as the carbon ion source. About 70% of the carbon from the vacuum arc is ionized, and 96 to 98% of the ionized carbon is monovalent ions, while the rest are divalent ions. It is also known that the ratio of divalent ions is further increased in a pulsed vacuum arc source. By using such a carbon ion source having a high polyvalent ion ratio, a high irradiation effect can be obtained even at a low bias voltage.

The hydrogen concentration in the DLC film can be determined by the HFS (Hydrogen Forward Scattering) method. Further, the hardness (nanoindenter hardness) and Young's modulus of the DLC film can be determined using a nanoindentation method (for example, nanoindenter manufactured by Toyo Technica Co., Ltd.).
Preferably, when the Young's modulus of the DLC film is 60 GPa or more, distortion of the film when stress is applied can be reduced, and chipping and peeling of the film are less likely to occur, thereby obtaining higher adhesion. Can do.

  The nanoindentation hardness of the DLC film is preferably 20 GPa to 70 GPa, and the thickness of the DLC film is preferably 0.5 μm to 5 μm.

  Hereinafter, examples of the present invention will be described in more detail, but the present invention is not limited thereto.

<Example 1-1>
SUS440C was used as the base material 1 of the sliding member, and the film structure shown in FIG. 1 was formed. After the substrate 1 was ultrasonically cleaned with acetone and isopropyl alcohol in advance, the substrate was attached to the substrate holder in the vacuum chamber. Next, the inside of the vacuum chamber was evacuated to a predetermined degree of vacuum while heating the substrate 1, and then a cleaning process with Ar gas was performed to clean the substrate surface. At this time, the ultimate vacuum was set to a low vacuum, and the oxygen concentration at the interface between the base material and the intermediate layer was increased by making it easily affected by residual moisture in the vacuum chamber. In addition, the Ar gas pressure during the cleaning process was set to be low, and the influence of residual moisture was remarkable.
Next, a Cr intermediate layer 2 was formed by sputtering a Cr target on the surface of the substrate 1. During the formation of the intermediate layer, oxygen was not supplied into the vacuum chamber.
Next, a negative bias voltage of several hundred volts was applied to the base material 1 on which the Cr intermediate layer 2 was formed, and a high concentration carbon layer was formed on the surface of the Cr intermediate layer 2 by carbon ion irradiation (carbon bombardment). Subsequently, the bias voltage was lowered to about several tens of volts to form an amorphous hard carbon film 3, and a sample of Example 1-1 was obtained. It was separately confirmed that when a high bias voltage of several hundred volts was applied, a part of the carbon ions entered the surface of the intermediate layer to form a high concentration carbon layer. It was also confirmed that when a low bias voltage was applied, carbon ions did not enter the intermediate layer and deposited on the intermediate layer surface to form a DLC film.
When the hydrogen content in the amorphous hard carbon film 3 was measured by HFS analysis, it was about 4 at% on the outermost surface and 1 at% or less inside the film.

<Example 1-2>
A sample of Example 1-2 was produced in the same manner as Example 1-1 except that Ti was used as a target for forming the intermediate layer.

<Example 1-3>
A sample of Example 1-2 was manufactured in exactly the same manner as Example 1-1 except that Si was used as a target for forming the intermediate layer.

<Example 2>
The same base material as in Example 1-1 was washed and placed in a vacuum chamber in the same procedure, and the inside of the vacuum chamber was evacuated to a predetermined degree of vacuum while heating the base material. Thereafter, a negative bias voltage of several hundred volts was applied to the substrate, and the substrate surface was cleaned by Cr ion bombardment by a vacuum arc source equipped with a Cr cathode. Thereafter, the bias voltage was lowered to form a Cr intermediate layer on the substrate.
Next, in the same manner as in Example 1-1, the surface of the intermediate layer was irradiated with carbon ions, an amorphous hard carbon film was formed, and the sample of Example 2 was produced.

<Comparative Example 1-1>
A sample of Comparative Example 1-1 was produced in the same manner as Example 1-1 except that the surface of the Cr intermediate layer 2 was not irradiated with carbon ions.

<Comparative Example 1-2>
A sample of Comparative Example 1-2 was produced in exactly the same manner as Example 1-2 except that the surface of the Ti intermediate layer 2 was not irradiated with carbon ions.

<Comparative Example 1-3>
A sample of Comparative Example 1-3 was produced in exactly the same manner as Example 1-3 except that the surface of the Si intermediate layer 2 was not irradiated with carbon ions.

<Comparative Example 1-4>
A sample of Comparative Example 1-4 was prepared in exactly the same manner as Example 1-1, except that Fe was used as a target for forming the intermediate layer, and the surface of intermediate layer 2 was not irradiated with carbon ions. .

<Comparative Example 1-5>
A sample of Comparative Example 1-5 was produced in exactly the same manner as Example 1-2, except that oxygen was added to the atmosphere during the formation of the intermediate layer.

<Comparative Example 2-1>
The sample of Comparative Example 2-1 was prepared in exactly the same manner as in Example 2 except that the intermediate layer was formed using a W cathode instead of the Cr cathode and the surface of the intermediate layer 2 was not irradiated with carbon ions. Produced.

<Comparative Example 2-2>
A sample of Comparative Example 2-2 was produced in exactly the same manner as Example 2 except that oxygen was added to the atmosphere during the formation of the intermediate layer.

<Comparative Example 3>
Using a SCM420 carburized material (surface carbon concentration of about 1 to 2 at%) as a base material, cleaning in the same procedure as in Example 1-1, placing in a vacuum chamber, and heating the base material in the vacuum chamber Was evacuated to a predetermined vacuum. Thereafter, a negative bias voltage of several hundred volts was applied to the substrate, and the substrate surface was cleaned by Cr ion bombardment by a vacuum arc source equipped with a Cr cathode. Thereafter, a sample of Comparative Example 3 was produced in the same manner as Example 1-1 except that the intermediate layer was not formed and carbon ion irradiation was not performed.

<Evaluation>
1. Measurement of oxygen concentration and carbon concentration of intermediate layer The depth profile of the sample was measured by SIMS analysis. 2 and 3 show the depth profile of the film of the sample of Example 1-1. As is clear from FIG. 2, it was confirmed that the oxygen concentration of the intermediate layer increased from the surface toward the inside, and reached the maximum concentration on the inner side (base material side). On the other hand, it was confirmed that the carbon concentration in the intermediate layer was maximum on the surface side and decreased toward the inside.
Moreover, when the vertical axis | shaft (oxygen concentration) of the depth profile of the sample of Example 1-1 corresponding to FIG. 3 and Comparative Example 1-5 was compared relatively, compared with Example 1-1, Comparative Example 1-5. It was found that the oxygen concentration on the surface of the intermediate layer was about 5 times higher.

2. 2. Evaluation of adhesion 2-1. Rockwell Indentation Test Using a Rockwell hardness meter (C scale, diamond indenter, load: 1.47 × 10 ⁷ Pa (150 kgf)), an indentation was made on the surface of each sample. The peeled state around the indentation was observed with an optical microscope and evaluated according to the following criteria.
○: No peeling of the film is observed ×: The peeling of the film is observed 2-2. Scratch test Using a diamond indenter (tip diameter 200 μm), the surface of each sample was scratched at a load speed of 100 N / min and a scratch speed of 10 mm / min, and the peeling start load of the film was measured. The measuring machine used was REVETEST manufactured by CSEM.
2-3. Actual machine test As the sliding member of the present invention, the coating structure of each of the above examples and comparative examples is formed on the piston ring and the valve lifter of the actual engine, and the sliding test (engine operation) is performed by incorporating it into the actual engine. went. In the case of a piston ring, the test was performed for 10 hours with an actual engine. In the case of a valve lifter, a 100-hour endurance test was performed using an actual head, and evaluation was performed according to the following criteria.
○: No peeling of the film is observed after the test ×: peeling of the film is observed after the test

3. Measurement of hardness Nano indentation (Diamond-type triangular pyramid type indenter (Barkovitch indenter) is an ultra-micro hardness meter that measures the amount of indentation when the indenter is indented under ultra-low load. The film hardness (nanoindenter hardness) and Young's modulus in the thickness direction of each sample were measured. As the nano indenter, NanoIndenter manufactured by MTS Systems was used.
FIG. 4 is a graph obtained by measuring the relationship between indentation depth and hardness by nanoindentation for the samples of Example 1-1 and Comparative Example 2-1. In the case of Example 1-1, it was confirmed that the hardness of the interface region between the DLC film and the intermediate layer was increased by the effect of irradiating the surface of the Cr intermediate layer with carbon ions.

  The results are shown in Table 1.

  As is clear from Table 1, in each case, the adhesion was excellent, and the film was not peeled even when an actual engine was used.

On the other hand, since carbon ion irradiation was not performed, in the case of Comparative Examples 1-1 to 1-3 and Comparative Example 2-1, in which carbide was not formed on the intermediate layer surface, the evaluation of adhesion with an actual machine was inferior.
Moreover, since the same material (Fe) as the base material was used as the intermediate layer and no carbon ion irradiation was performed, in the case of Comparative Example 1-4 where no carbide was formed on the surface of the intermediate layer, the adhesion evaluation was Also inferior.
In the case of Comparative Example 1-4 in which carbide was not formed on the intermediate layer surface because the same material (Fe) as that of the base material was used as the intermediate layer and carbon ion irradiation was not performed, the evaluation of adhesion was a laboratory evaluation. All of the actual machine evaluations were inferior.

Since oxygen was added to the atmosphere during the formation of the intermediate layer, in the case of Comparative Example 1-5 and Comparative Example 2-2 in which the oxygen concentration on the surface of the intermediate layer was higher than that of the example, the evaluation of adhesion was a laboratory evaluation. And the actual machine evaluation were inferior.
In the case of Comparative Example 3 in which no intermediate layer was formed, the adhesion evaluation was inferior in both the laboratory evaluation and the actual machine evaluation.

It is a schematic diagram which shows the cross section of the sliding member which concerns on embodiment of this invention. It is a figure which shows the depth profile of the film | membrane of the sample of Example 1-1. It is another figure which shows the depth profile of the film | membrane of the sample of Example 1-1. It is a figure which shows the graph which measured the relationship of the indentation depth by the nanoindentation of the sample of an Example, and hardness.

Explanation of symbols

1 Base material 2 Intermediate layer 3 Amorphous hard carbon film

Claims (5)

A base material, an intermediate layer formed on the surface of the base material, and an amorphous hard carbon film formed on the surface of the intermediate layer and containing hydrogen as a main component and having a hydrogen content of 5 at% or less,
A sliding member in which the oxygen concentration of the intermediate layer increases from the surface side toward the inside of the intermediate layer, and the carbon concentration decreases from the surface side toward the inside of the intermediate layer.   The sliding member according to claim 1, wherein Young's modulus of the amorphous hard carbon film is 60 GPa or more.   The sliding member according to claim 1 or 2, wherein the intermediate layer and the amorphous hard carbon film are formed by a vacuum arc deposition method.   The sliding member according to any one of claims 1 to 3, wherein the intermediate layer is made of a metal layer having a standard free energy of formation of oxide at 100 ° C of -600 kJ or less.   The sliding member according to any one of claims 1 to 4, wherein the intermediate layer is made of a metal layer including one or more selected from the group consisting of Si, Ti, and Cr.

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