JP2006124806A - Hard carbon film sliding member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hard carbon film sliding member which can obtain a low friction coefficient even in lubricant such as engine oil and transmission oil, can be produced by a simple process, and has reduced restriction in the kinds of lubricants. <P>SOLUTION: Regarding a sliding member obtained by providing a hard carbon film at least on the sliding part with a mating member, magnesium is incorporated into the hard carbon film, and the content thereof is controlled to the range of 2 to 41 atomic%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sliding member provided with a hard carbon coating excellent in low friction characteristics, and in particular, a low-friction hard carbon coating sliding member suitable for use in lubricating oil such as engine oil and truss mission oil. It is about.

  The hard carbon film is a film made of amorphous carbon or hydrogenated carbon, and includes aC: H (amorphous carbon or hydrogenated amorphous carbon), iC (eye carbon), DLC (diamond-like carbon or dee carbon). Elsie).

In order to form such a hard carbon film, a gas phase synthesis method such as a plasma CVD method in which a hydrocarbon gas is plasma-decomposed or an ion beam evaporation method using carbon or hydrocarbon ions is used. This hard carbon coating has a high hardness, a smooth surface, excellent wear resistance, and a low friction coefficient due to its solid lubricity, and has excellent sliding characteristics.
For example, the friction coefficient of non-lubricated surface of a normal smooth steel material is 0.5 to 1.0, whereas in the hard carbon film, the friction coefficient of non-lubricated is about 0.1. is there.

  Hard carbon coatings take advantage of the above-mentioned excellent characteristics, and are non-lubricated such as cutting tools such as drill blades and grinding tools, plastic working dies, valve cocks and capstan rollers. It is applied to sliding parts below.

  On the other hand, in mechanical parts such as internal combustion engines that slide in lubricating oil, there is a desire to reduce mechanical loss as much as possible from the viewpoint of energy consumption and environmental problems. In addition to providing a hard carbon coating on the sliding member and controlling its composition and surface condition, the friction coefficient is not only in a non-lubricated state but also in the presence of sufficient lubricating oil. Several attempts have been made to lower

For example, a method of adding one or more of IVa, Va, VIa group elements and Si to such a hard carbon coating is shown, and this method reduces the friction coefficient compared to the case where these elements are not added. (See Patent Document 1).
In addition, a method of providing Ag clusters on such a hard carbon coating is also shown (see Patent Document 2).
In addition, a low friction coefficient is obtained by adding an appropriate metal element to such a hard carbon film and further controlling the oxygen content in the film (see Patent Document 3).
JP 2003-247060 A JP 2004-099963 A JP 2004-115826 A

However, in the method described in Patent Document 1, there is a demand for a further reduction in the friction coefficient from 0.06, which is the friction coefficient in the motoring test, despite the influence of the difference in the measurement method. Also, in the method described in Patent Document 2, since the friction coefficient is measured by a reciprocating test, a direct comparison is not possible, but the friction coefficient is 0.04 at the minimum, and similarly, another friction coefficient. Reduction is desired. Moreover, since it is necessary to provide an Ag cluster by controlling the size and number on the hard carbon film, there is a complicated aspect in terms of process control.
Furthermore, in Patent Document 3, since it is necessary to control both the content of the metal element and the content of oxygen, a simpler process is desired. Further, in this case, since an extreme pressure additive such as molybdenum dithiocarbamate (MoDTC) is required in the lubricating oil, there is a problem that the types of lubricating oil that can exert the effect are limited.

  In view of the above-described problems, the present invention provides a hard carbon film sliding member that can be manufactured by a simple process and the type of lubricating oil that is effective is not limited while further reducing the friction coefficient. It is aimed.

  In order to achieve the above object, the inventors of the present invention have made extensive studies on the types and methods of film formation of hard carbon films, and methods for doping hard carbon films with metal elements as additive components. In order to maximize the effect of friction reduction, various knowledge about the optimum addition amount and the composition of the carbon coating as a base material was obtained, and the present invention was developed. It came to completion.

  That is, the present invention is based on the above knowledge, and the hard carbon film sliding member of the present invention is included in the hard carbon film of the sliding member provided with a hard carbon film at least at a sliding portion with a counterpart material. It is characterized by containing 2 atomic% or more and 41 atomic% or less of magnesium, and can be suitably used particularly in lubricating oils such as automobile engine oil and transmission oil.

  According to the present invention, in a hard carbon film sliding member having a hard carbon film at least at a sliding portion with a counterpart material, magnesium is added to the hard carbon film, and the range of the magnesium content is optimized. Therefore, the friction coefficient can be greatly reduced, and the effect can be remarkably exhibited particularly when used in lubricating oil such as engine oil and transmission oil for automobiles.

Hereinafter, the hard carbon film sliding member of the present invention will be described in more detail.
The hard carbon film sliding member of the present invention is provided with the hard carbon film containing 2 atomic% or more and 41 atomic% or less of magnesium as described above, which can greatly reduce the friction coefficient. Although it is possible, the reason why the hard carbon film exhibits a low coefficient of friction can be estimated as follows, although it is not always clear at the present time.
That is, by adding magnesium to the coating, the surface of the hard carbon coating is improved in the ability to adsorb the base (base oil) component in the lubricant and the additive component contained in the lubricant. A thin film of base oil or additive is formed. As a result, even under conditions where the surface pressure is high or the sliding speed is low, so-called boundary lubrication conditions, it is thought that a low coefficient of friction is manifested by the mechanism in which the formed film prevents direct contact with the mating material. It is done.

  At this time, it is not always necessary to contain magnesium from the surface to the deep part of the hard carbon vat. It is sufficient to contain magnesium to the sliding surface and at least the part corresponding to the reduction due to wear.

  When the amount of magnesium added is less than 2 atomic%, the above adsorption effect is not sufficiently exhibited. On the other hand, if it exceeds 41 atomic%, the low friction performance inherently possessed by the hard carbon coating is impaired because the network structure of carbon atoms is disturbed by the presence of magnesium atoms.

The hard carbon film sliding member of the present invention can be used even under conditions where no lubricant is used (so-called dry conditions). However, as described above, adsorption with the base (base oil) and additives of the lubricant is not possible. Since it is the essence of lowering the friction coefficient, the effect is further exhibited by using it in the lubricant.
Therefore, it is preferably used in a lubricant. Examples of such a lubricant include automobile engine oil and transmission oil.

In order to obtain a low coefficient of friction in such a lubricating oil, it is preferable to reduce the amount of hydrogen atoms in the coating. The specific range is preferably 6 atomic% or less, more preferably 1 atomic% or less.
Note that such a hard carbon film having a low hydrogen content is formed by a PVD method (physical vapor deposition method) that does not substantially use hydrogen or a hydrogen-containing compound, such as a sputtering method or an ion plating method. Can be obtained by:

  Examples of the present invention will be described below together with comparative examples. Needless to say, the embodiment described below is not necessarily required as long as it satisfies the claims of the present invention.

Example 1
A 30 mm diameter and 3 mm thick disk made of carburized steel (Japanese Industrial Standard SCM415) was prepared as a base material, and after superfinishing the surface to Ra 0.020 μm, the surface of the base material was hardened by magnetron sputtering. A carbon film was coated.
As the sputtering target, a disk made of graphite and having a radius of 80 mm is used. By placing a metal magnesium plate on the carbon target, a certain amount of magnesium is contained in the hard carbon film simultaneously with the sputtering of carbon. I made it. At this time, the magnesium plate had a sector shape with a radius of 80 mm and an apex angle of 7.5 °, and the magnesium plate occupied 1/48 of the entire target. Argon was used as the atmosphere gas for sputtering.

As for the process time, the film formation rate is obtained without using a magnesium plate in advance, and this is applied to the case with a magnesium plate to estimate the film formation rate so that the film thickness is 1.0 ± 0.3 μm. Set to.
After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.016 μm.

Next, the element in the film was analyzed for the obtained hard carbon coating.
With respect to magnesium, X-ray photoelectron spectroscopy (XPS) was used, taking into account impurity adsorption on the outermost surface, and the magnesium content at a position of 3 nm from the sample surface was taken as a representative value. As a result of the measurement, the magnesium content was 24 atomic%.
On the other hand, the amount of hydrogen atoms was measured using a secondary ion mass spectrometry (SIMS) while digging up to a position of 5 nm from the sample surface, and the hydrogen content at a position of depth of 3 nm was taken as a representative value. As a result, the amount of hydrogen was 0.1 atomic% or less.

Next, the friction characteristics of the sample were evaluated by a ball-on-disk method. In the test, automotive engine oil 5W-30SL was used as a lubricant.
The sample was rotated in the engine oil, a 6 mm diameter ball made of bearing steel (Japanese Industrial Standard SUJ2) was pressed, and the friction coefficient was calculated by measuring the torque applied to the arm holding the ball. The diameter of the sliding mark was 8 mm, and the oil temperature was 80 ° C. Further, the vertical load applied to the ball is 10N. The ball was fixed so that it would not roll by sliding. The sliding speed was 2.6 cm per second.

  Regarding the calculation of the friction coefficient, taking into account the familiar effect immediately after the start of sliding, the measured value at the time when 5 minutes had elapsed from the start of the test was regarded as the friction coefficient of the material. The friction coefficient of the hard carbon coating of this example was 0.022. These results are shown together in Table 1 together with the film forming conditions.

(Example 2)
Similar to Example 1, a hard carbon film was coated on the same base material surface by magnetron sputtering using carbon as a target.
As a sputtering target, a fan-shaped magnesium oxide plate having a radius of 80 mm and an apex angle of 3.75 ° is placed on a disk-like carbon target having a radius of 80 mm so that the magnesium oxide occupies 1/96 of the entire target. Similarly, the process time was set so that the film thickness was 1.0 ± 0.3 μm.

After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.018 μm.
Next, as in Example 1, the amounts of magnesium and hydrogen were quantified. As a result, they were 13 atomic% and 0.1 atomic% or less, respectively. Moreover, it was 0.019 as a result of measuring a friction coefficient similarly. These results are also shown in Table 1.

(Example 3)
Similar to Example 1, a hard carbon film was coated on the same base material surface by magnetron sputtering using carbon as a target.
As a sputtering target, a fan-shaped metal magnesium plate having a radius of 80 mm and an apex angle of 15 ° is placed on a disk-like carbon target having a radius of 80 mm so that magnesium occupies 1/24 of the entire target. The process time was set to a thickness of 1.0 ± 0.3 μm.

After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.020 μm.
Subsequently, the amount of magnesium and the amount of hydrogen were determined in the same manner as in Example 1, and the friction coefficient was measured in the same manner. As a result, the magnesium amount was 40 atomic%, the hydrogen amount was 0.1 atomic% or less, and the friction coefficient was 0. 0.023. These results are also shown in Table 1.

Example 4
Similar to Example 1, a hard carbon film was coated on the same base material surface by magnetron sputtering using carbon as a target.
As a target, a fan-shaped metal magnesium plate having a radius of 80 mm and an apex angle of 1.875 ° is placed on a disk-shaped carbon target having a radius of 80 mm so that magnesium occupies 1/192 of the whole target, and the like. The process time was set to a thickness of 1.0 ± 0.3 μm.

After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.020 μm.
Then, as in Example 1 above, the amount of magnesium and the amount of hydrogen were quantified, and the friction coefficient was measured in the same manner. As a result, the amount of magnesium was 2.3 atomic%, the amount of hydrogen was 0.1 atomic% or less, and the friction The coefficient was 0.021. These results are also shown in Table 1.

(Example 5)
Similar to Example 1, a hard carbon film was coated on the same substrate surface by magnetron sputtering using carbon as a target.
As in the case of Example 1, the process time was set so that the metal magnesium plate occupied 1/48 of the entire target and the film thickness was 1.0 ± 0.3 μm in the same manner as in Example 1. Note that, as the atmosphere gas for sputtering, instead of pure argon, a mixture of argon and methane gas at a ratio of 90:10 was used.

After completion of the process, the surface roughness of the sample was measured and found to be Ra 0.015 μm.
Next, as in Example 1, the amount of magnesium and the amount of hydrogen were determined, and the friction coefficient was measured in the same manner. As a result, the magnesium amount was 17 atomic%, the hydrogen amount was 7 atomic% or less, and the friction coefficient was 0. 034. These results are also shown in Table 1.

(Example 6)
Similar to Example 1, a hard carbon film was coated on the same substrate surface by magnetron sputtering using carbon as a target.
As in the same manner as in Example 1, a target in which the metal magnesium plate occupies 1/48 of the entire target was used, and the process time was similarly set so that the film thickness was 1.0 ± 0.3 μm. did. Note that, as the atmosphere gas for sputtering, instead of pure argon, a mixture of argon and methane gas at a ratio of 98: 2 was used.

After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.023 μm.
Next, as in Example 1 above, the amount of magnesium and the amount of hydrogen were determined, and the friction coefficient was measured in the same manner. As a result, the magnesium amount was 19 atomic%, the hydrogen amount was 1.4 atomic% or less, and the friction coefficient was 0.032. These results are also shown in Table 1.

(Comparative Example 1)
Similar to Example 1, a hard carbon film was coated on the same base material surface by magnetron sputtering using carbon as a target. However, in the comparative example, the process time was set so that the film thickness was 1.0 ± 0.3 μm without placing metal magnesium or magnesium oxide on the carbon target.

The surface roughness of the sample after film formation was Ra 0.019 μm. Similarly, as a result of quantitative determination of the magnesium amount and the hydrogen amount, both were 0.1 atomic% or less.
Furthermore, as a result of measuring the friction coefficient in the same manner, it was 0.047. These results are also shown in Table 1.

(Comparative Example 2)
Similar to Example 1, a hard carbon film was coated on the same base material surface by magnetron sputtering using carbon as a target.
As a sputtering target, a fan-shaped magnesium oxide plate having a radius of 80 mm and an apex angle of 30 ° is placed on a disk-like carbon target having a radius of 80 mm so that magnesium occupies 1/12 of the entire target. The process time was set to a thickness of 1.0 ± 0.3 μm.

After the process was completed, the surface roughness of the sample was measured and found to be Ra 0.024 μm.
Subsequently, the amount of magnesium and the amount of hydrogen were determined in the same manner as in Example 1, and the friction coefficient was measured in the same manner. As a result, the magnesium amount was 46 atomic%, the hydrogen amount was 0.1 atomic% or less, and the friction coefficient was 0. .039. These results are also shown in Table 1.

  As is apparent from the results in Table 1, the hard carbon film sliding member of the comparative example substantially not containing magnesium or containing more than 41 atomic% has a high friction coefficient in the lubricating oil. On the other hand, in the hard carbon film sliding member of the present invention containing a specific range of magnesium in the film, it exhibits a low coefficient of friction, in particular, by reducing the hydrogen content to 0.1 atomic% or less, extremely low It was confirmed to show friction characteristics.

Claims (6)

  A sliding member provided with a hard carbon coating at least at a sliding portion with a counterpart material, wherein the coating contains magnesium in an amount of 2 atomic% or more and 41 atomic% or less. Element.   The hard carbon film sliding member according to claim 1, wherein the amount of hydrogen in the film is 6 atomic% or less.   The hard carbon film sliding member according to claim 1, wherein the amount of hydrogen in the film is 1 atomic% or less.   The hard carbon film sliding member according to any one of claims 1 to 3, wherein the hard carbon film sliding member is used in a lubricant.   The hard carbon film sliding member according to claim 4, wherein the lubricant is an engine oil for automobiles.   The hard carbon film sliding member according to claim 4, wherein the lubricant is a transmission oil for automobiles.