JP7164880B2 - Hard carbon film, manufacturing method thereof, and sliding member - Google Patents

Description

The present invention relates to a hard carbon film, a method for producing the same, and a sliding member having the hard carbon film formed thereon.

Sliding members are widely used in industrial applications such as various machines, automobiles, home appliances, and general household machines and devices, and various technologies have been developed to achieve even lower friction and higher wear resistance. It is

As such a technique, in recent years, friction modifiers such as MoDTC (molybdenum dithiocarbamate) have been developed to lower the coefficient of friction, and are added to lubricating oils such as engine oils. When engine oil containing MoDTC is applied, when steel materials slide against each other, MoDTC decomposes and forms a low-shear tribofilm composed of MoS ₂ on the surface of the steel materials, which reduces the coefficient of friction. The steel material wears away at places where the surface pressure is high, such as parts of the lifter, rocker arm, piston pin, etc., and durability cannot be ensured.

Therefore, instead of sliding between steel materials, hard carbon (DLC: It has been proposed to provide a diamond-like carbon) film.

In particular, a hydrogen-free (hydrogen-free) hard carbon film called a ta-C film (tetrahedral amorphous carbon film) is terminated with an OH group on the surface of the hard carbon, so that it can be used in lubricating oils such as engine oil. Due to its extremely low friction characteristics, it is used in many engine parts such as valve lifters and piston rings.

However, when such a ta-C film is used in MoDTC-added engine oil, almost no tribofilm is formed, and the generation of OH groups on the ta-C film surface is inhibited, so the friction coefficient I'm having a problem with not going down.

In addition, a ta-C film is generally formed using an arc ion plating method (also referred to as a “vacuum arc deposition method”), but a ta-C film formed using an arc ion plating method , hard carbon macroparticles, also called droplets, are inevitably produced. When the ta-C film in which many droplets are generated is slid, the mating material is greatly worn by abrasive wear. In addition, since the dropped droplets have hardness equivalent to that of the ta-C film, the dropped droplets wear the ta-C film itself.

As a method for preventing the formation of droplets in such a ta-C film, carbon ions, which are the raw material for film formation, and graphite fine particles, which are the starting point for droplet formation, are separated by a filter using an electromagnetic field or the like, and carbon ions are separated. Although it is conceivable to form a ta-C film with only a single filter, if advanced filtering is attempted, part of the carbon ions will also be captured by the filter, resulting in a decrease in carbon ions involved in the film formation. This decrease in carbon ions causes a drastic decrease in the film formation rate compared to the normal arc ion plating method, resulting in a great decrease in productivity. Also, advanced filtering requires large-scale equipment, which greatly increases costs.

Therefore, the droplets are usually removed by lapping after film formation. However, since the droplets are bonded to the ta-C film, though not as much as the ta-C films, it is difficult to sufficiently remove the droplets even by lapping. Strong lapping makes it easier to remove the droplets, but may damage the ta-C film itself. In addition, the introduction of a lapping device and the provision of a separate lapping process lead to an increase in cost.

As the hard carbon film, in addition to the above-described ta-C film, an aC:H film ( There is a hydrogen-containing hard carbon film called a hydrogenated amorphous carbon film. This aC:H film does not produce the droplets described above, but when used in MoDTC-added engine oil, after temporarily showing low friction, it is abnormally worn and worn, resulting in reduced durability. A problem arises. The reasons for such abnormal wear and abrasion and reduced durability are the sp ² structure resulting from the unsaturated six-membered ring structure in the aC:H film and the decomposition of MoDTC to form MoS ₂ MoO ₃ produced during the formation of the low-shear tribofilm is combined with the substance produced by desorption from the aC:H film.

In such a hard carbon film, for example, metal elements such as Cr, W, Co, and Ti are added to the ta-C film to form a tribofilm on the surface of the metal elements, thereby reducing the coefficient of friction. Attempts have been made, but in this case, the film hardness is greatly reduced, resulting in problems such as extremely large physical wear.

Under such circumstances, for the purpose of increasing the adhesive strength with the base material, a hard carbon film (ta-C film) formed by the arc ion plating method and a hard carbon film (a-C film) formed by the CVD method were formed. H film) has been proposed (for example, Patent Documents 1 and 2). However, simply laminating two types of hard carbon films, a ta-C film and an aC:H film, can increase the adhesion to the base material, but the above-mentioned low friction and resistance It is difficult to sufficiently improve wearability.

JP-A-2000-128516 JP-A-2002-322555

In view of the above-mentioned problems, the present invention effectively suppresses the occurrence of abrasive wear while maintaining wear resistance and seizure resistance in a sliding member used in a lubricating oil containing MoDTC. To provide a hard carbon film manufacturing technology for manufacturing a hard carbon film having a greatly reduced coefficient of friction without lowering productivity or increasing costs.

In investigating the solution of the above problems, the present inventors investigated in detail the droplets generated during the formation of the ta-C film using the arc ion plating method. As a result, droplets are conventionally generated by the graphite evaporation source being damaged by the impact of the arc discharge during the film formation by the arc ion plating method and scattering as graphite fine particles. However, it was actually found to be sp3 ^- rich protuberant morphology growing in a cone-like shape with dispersed graphite fine particles as nuclei.

Since the sp3 ^- rich structure has the same structure as the deposited hard carbon film (ta-C film), this protuberance-like morphology is very hard and can easily break off from the hard carbon film. will damage the hard carbon film. On the other hand, when it does not come off from the hard carbon film, it can contribute to the improvement of durability together with the hard carbon film.

Therefore, the present inventors found that when an aC:H film is formed so as to cover the protruding features generated during the formation of this ta-C film, not only does the protruding feature not fall off, but also wear resistance is achieved. We thought that even an aC:H film, which cannot be said to have excellent properties, can exhibit excellent wear resistance in a MoDTC-containing lubricating oil due to the raised morphology, and conducted experiments and studies. rice field.

As a result, when the aC:H film is formed so as to be laminated on the taC film, the aC:H film on the surface layer is first worn during sliding in the MoDTC-containing lubricating oil. Although the protruding morphology begins to be exposed, this protruding morphology is bonded to the ta-C film and is embedded in the aC:H film, so it does not fall off easily. It was found that it functions as a strut to suppress the wear of the aC:H film, gradually reducing the wear rate of the hard carbon film.

That is, as the above process proceeds, first, the aC:H film having a relatively low hardness is worn away, and the surface of the hard carbon film is smoothed at the nano level. As a result, the overall surface pressure is lowered, and the progress of wear of the aC:H film is stopped. At this time, on the surface of the hard carbon film, a sea-island structure is formed in which protuberances having the same structure as the ta-C film are scattered in the aC:H film. has the same structure as the ta-C film and the tip of the high hardness protuberant form functions as a support for the aC:H film, so that not only does wear hardly progress anymore, but also the friction coefficient is greatly increased. It was found that the surprising result of lowering was obtained, leading to the completion of the present invention.

It is considered that the reason why the coefficient of friction is greatly reduced is that the following effects (1) to (4) are combined.

(1) Smoothing effect, that is, effect due to smoothing accompanying wear of the aC:H film.
(2) Since the aC:H film occupies a wide area on the surface of the hard carbon film, unlike the case of the ta-C film, the tribofilm is formed on the sliding partner side.
(3) Since the size of the protuberances having the same structure as the ta-C film is at the submicron level, the hard carbon film is finally formed on the high-hardness ta-C film with a low-hardness a - C: The effect of forming an H film with a submicron thickness and forming an ideal layer structure that exhibits low friction.
(4) The effect of reducing the contact area due to sliding on the protuberant form.

As described above, according to the present invention, two kinds of hard carbon films are laminated, and the protrusions are protruded from the first hard carbon film on the lower layer side toward the second hard carbon film on the upper layer side. As a result, even in the MoDTC-containing lubricating oil, the abrasive wear caused by falling off of the bumps can be reduced, and a sufficiently low coefficient of friction can be obtained.

And, in a sliding member used in a lubricating oil containing MoDTC, while maintaining wear resistance and seizure resistance, it is possible to effectively suppress the occurrence of abrasive wear and significantly reduce the coefficient of friction. can be done.

Such a hard carbon film does not require an expensive filter because there is no need to remove the protuberances that are produced, and there is no particular need for lapping, so there is no increase in cost. , does not lead to a decrease in productivity.

In addition, as in the present invention, there is JP 2016-60921 as a technique for achieving low friction and wear resistance in lubricating oil by laminating a ta-C film and aC:H film. This technique, which polishes down to the underlying ta-C film to remove the raised features, makes the sp2 in the ta-C film considerably higher ( ^Ecd / Ecg of 1.7 to 3.8) is necessary, and there is no idea of positively using a protuberance-like morphology as in the present invention.

Based on the above knowledge, the present inventors further investigated the specifically preferred density of the protuberances on the surface of the hard carbon film. As a result, in the state immediately after the second hard carbon film was produced, the number of microprotrusions in the protruding form protruding from the surface was 80 per 1.25 mm of measurement length on a straight line extending in the direction along the surface. ~300 has been found to be preferred. However, during actual use, the minute protrusions on the surface of the hard carbon film may be scraped off and flattened by lapping or the like after the aC:H film (second hard carbon film) is formed. In this case, it is necessary to confirm the number of bumps in the cross section of the hard carbon film. is preferred. Furthermore, even when the surface of the substrate on which the hard carbon film is formed is rough and projections are formed on the surface of the hard carbon film due to the roughness of the substrate surface, and it is difficult to count the number of microprotrusions due to the protruding morphology, It is necessary to confirm the number of protruding features in the cross section of the hard carbon film, and the number of protruding features in the cross section of the hard carbon film is preferably 8 to 30 per 125 μm measurement length on a straight line extending in the direction along the surface.

In addition, as a result of further experiments, the first hard carbon film is not limited to the ta-C film as long as the protruding morphology is formed, and the second hard carbon film is not limited to the formation of protruding morphology. However, as long as the hardness is lower than that of the first hard carbon film, it is not limited to the aC:H film.

The inventions according to claims 1 to 3 are based on the above findings, and the invention according to claim 1,
A hard carbon film coated on the sliding surface of the sliding member,
The first hard carbon film on the lower layer side and the second hard carbon film on the upper layer side are laminated,
The second hard carbon film has a lower hardness than the first hard carbon film,
The first hard carbon film is formed with a plurality of protrusions protruding toward the second hard carbon film,
The second hard carbon film has a thickness of 0.1 to 0.5 μm,
the tip of the raised form is exposed from the surface of the second hard carbon film,
the first hard carbon film is a ta-C film,
the second hard carbon film is an aC:H film,
The protruded form is a hard carbon film characterized by having the same structure as the first hard carbon film.

In addition, the invention according to claim 2 ,
The number of microprotrusions derived from the raised morphology formed on the first hard carbon film is 80 per 1.25 mm measured length on a straight line extending in the direction along the surface on the surface of the hard carbon film. 3. The hard carbon film according to claim 1, wherein the number is 300.

In addition, the invention according to claim 3 ,
8 to 30 protruding features formed on the first hard carbon film per 125 μm measured length on a straight line extending along the surface in the cross section of the hard carbon film. It is a hard carbon film according to claim 1 .

As described above, the protuberances are embedded in the second hard carbon film, so they are prevented from coming off from the hard carbon film. When the tip of the protuberant form penetrates through the second hard carbon film and is exposed to the surface, the function of the second hard carbon film as a support is exhibited remarkably. In addition, since the tip of the cone-shaped protuberance is spherical, the coefficient of friction is sufficiently reduced.

A hard carbon film in which the tips of such protuberances are exposed from the surface of the second hard carbon film can be produced by lapping the surface of the second hard carbon film.

The invention according to claim 4 ,
The ratio of the area ID of the D peak to the area IG of the G peak obtained from the Raman spectrum of the first hard carbon film (ID/IG ratio) is 0.2 to 0.8. A hard carbon film according to any one of claims 1 to 3 .

Since the ID/IG ratio is known to correlate with the sp ³ /(sp ² +sp ³ ) ratio in hard carbon films, the hardness of carbon films can be estimated by using this ID/IG ratio. can be done. Specifically, the higher the ID/IG ratio ^, the lower the ratio of sp3 and the lower the hardness.

By arranging the first hard carbon film with high hardness such as an ID/IG ratio of 0.2 to 0.8 on the lower layer side, a hard carbon film having a higher abrasion resistance can be obtained by the raised morphology of the same structure. can be provided.

The invention according to claim 5 ,
5. The hard carbon film according to any one of claims 1 to 4 , wherein the first hard carbon film has a hydrogen content of 15 atom % or less.

A hard carbon film having a hydrogen content of 15 atom % or less has a high hardness. Such a hard carbon film is formed as a first hard carbon film, and a protuberant form having the same structure is formed on the surface of the first hard carbon film. By providing, excellent wear resistance can be exhibited.

The invention according to claim 6 ,
6. The hard carbon film according to any one of claims 1 to 5 , wherein the second hard carbon film has a hydrogen content of 20 atom % or more.

A hard carbon film with a hydrogen content of 20 atom % or more has a low hardness, and when such a second hard carbon film is worn by sliding, the protuberances can be easily exposed on the surface. . In addition, it can exhibit more excellent low friction properties in MoDTC-containing lubricating oil. Note that if the hydrogen content increases and the difference in hardness and internal stress between the first hard carbon film and the second hard carbon film becomes too large, separation between the films is likely to occur. The upper limit of the amount is preferably 40 atom %.

Since the height of the protrusions formed on the first hard carbon film is usually about 0.5 μm or less, the second hard carbon film should be formed to a thickness of 0.1 to 0.5 μm. can obscure raised features that are less than their thickness to form a relatively flat sliding surface. The second hard carbon film with low hardness is rapidly worn by sliding in the MoDTC-containing lubricating oil. , a low coefficient of friction and wear resistance can be achieved. In addition, even in the above case, it is also possible to intentionally expose the protuberant form by lapping or the like.

The invention according to claim 7 ,
7. The hard carbon film according to any one of claims 1 to 6 , wherein the second hard carbon film contains 1 to 20 atom % of any one of a metal element, nitrogen, and boron. is.

When these elements are added, the hardness of the second hard carbon film is lowered and a tribofilm is likely to be formed, so that lower friction properties can be exhibited, but on the other hand, wear resistance is lowered. However, in the present invention, the wear resistance is ensured by using the protuberances having the same structure as the first hard carbon film as pillars, so that the wear resistance is not deteriorated. In addition, Cr, Fe, Si, W, Ti etc. can be mentioned as a specific metal element.

The invention according to claim 8 ,
A sliding member having a sliding surface coated with the hard carbon film according to any one of claims 1 to 7 , wherein the sliding member slides in MoDTC-containing oil. be.

The sliding member whose sliding surface is coated with the hard carbon film described above effectively suppresses the occurrence of abrasive wear while maintaining wear resistance and seizure resistance even when used in MoDTC-containing lubricating oil. At the same time, the coefficient of friction can be significantly reduced.

By forming a first hard carbon film on a base material using an arc ion plating method, a plurality of bumps are grown on the surface of the first hard carbon film with high hardness, and scattered can be made

Then, by using a CVD method or a sputtering method to form a second hard carbon film having a low hardness on the first hard carbon film, protuberances are scattered in the second hard carbon film. A sliding member formed with a hard carbon film that suppresses the occurrence of abrasive wear and significantly reduces the coefficient of friction while maintaining wear resistance and seizure resistance even in MoDTC-containing lubricating oil. can be

First, by increasing the arc current to 40 A or more, the graphite evaporation source is damaged, and the frequency of discharging fine particles of graphite that serve as starting points for the formation of protuberances increases. It can form the origin of the formation of things.

Thereafter, by reducing the arc current to more than 0 A and 40 A or less, it is possible to suppress the formation of protuberances that are relatively easy to fall off and begin to form near the outermost layer of the first hard carbon film. As a result, the starting points of the formation of protuberances are concentrated in the range of 0.1 to 0.3 μm from the surface of the first hard carbon film, and these grow almost uniformly to form the second hard carbon film. The height of the raised features protruding through the membrane is uniform.

In the formation of the first hard carbon film using the arc ion plating method, when the arc discharge is extinguished and re-ignited, a large amount of macroparticles (graphite fine particles), which serve as starting points for the formation of protuberances, scatter. Therefore, since a relatively large amount of these macroparticles are included at a certain thickness position of the hard carbon film, by extinguishing and reigniting the arc discharge near the film surface, the macroparticles are generated in the vicinity of the film surface. The protuberance-like features grow substantially uniformly, the density of the protuberance-like features protruding through the second hard carbon film increases, and the protrusion height becomes uniform.

As a result, the number of the tip portions of the protuberance-shaped portion that contacts the mating sliding member is increased, so that it is possible to improve the abrasion resistance and reduce the coefficient of friction.

According to the present invention, in a sliding member used in a lubricating oil containing MoDTC, while maintaining wear resistance and seizure resistance, the occurrence of abrasive wear is effectively suppressed, and the coefficient of friction is greatly improved. It is possible to provide a hard carbon film manufacturing technique for manufacturing a hard carbon film with a reduced σ without lowering productivity or increasing costs.

FIG. 4 is a cross-sectional view schematically showing the manufacturing process of the hard carbon film according to the embodiment of the invention; 1 is a schematic cross-sectional view of a hard carbon film according to an embodiment of the invention; FIG. 1 is a diagram schematically showing the surface of a hard carbon film of the invention according to an embodiment of the invention; FIG. It is explanatory drawing of a sliding test. It is a figure which shows the test result of a sliding test. It is a figure which shows the test result of a sliding test. It is a figure which shows the test result of a sliding test.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described based on embodiments with reference to the drawings. In the following description, the ta-C film is used as the first hard carbon film, and the aC:H film is used as the second hard carbon film.

FIG. 1 is a cross-sectional view schematically showing the manufacturing process of the hard carbon film according to the present embodiment, showing that the process progresses in order from (a) to (c). FIG. 2 is a schematic cross-sectional view of the hard carbon film, in which (a) is a state in which only the aC:H film is formed on the base material and is abnormally worn, and (b) is a ta-C film. (c) is the aC:H film (second hard carbon film) on the ta-C film (first hard carbon film) containing no bumps. ) is formed and the aC:H film is abnormally worn. It shows a state where FIG. 3 is a diagram schematically showing the surface of the hard carbon film according to this embodiment. In FIGS. 1 to 3, 1 is a base material for forming a hard carbon film, 2 is a ta-C film as the first hard carbon film, 3 is a protruding form, and 4 is a second hard carbon film. It is an aC:H film as.

(1) Structure of hard carbon film As shown in FIG. 1, the hard carbon film according to the present embodiment is first formed by arc ion plating to form a ta-C film 2 containing a large amount of bumps 3. It is formed on the base material 1 . After that, the aC:H film 4 is formed on the ta-C film 2 by using the CVD method or the sputtering method so as to cover the raised features 3, thereby manufacturing the hard carbon film according to the present embodiment. be done. At this time, the raised features 3 are scattered on the surface of the aC:H film 4 at a predetermined density. A preferable density is that the number of microprotrusions on the surface of the hard carbon film is 80 to 300 per 1.25 mm of measurement length on a straight line extending in the direction along the surface, or the number of protuberances is 80 to 300 in the cross section of the hard carbon film. , from 8 to 30 per 125 μm measured length on a straight line extending in the direction along the surface.

In this way, when the aC:H film 4 is formed so as to cover the protruding features 3 formed on the ta-C film 2, not only does the protruding feature 3 not drop off, but also as shown in FIG. As shown in d), the protuberances 3 serve as pillars to suppress the wear of the aC:H film 4, so even when used in a MoDTC-containing lubricating oil, wear resistance and seizure resistance are improved. While maintaining this, it is possible to suppress the occurrence of abrasive wear and significantly reduce the coefficient of friction.

In contrast, when only the aC:H film is formed on the base material, the aC:H film is abnormally worn as shown in FIG. 2(a). Then, when only the ta-C film is formed on the base material, as shown in FIG. Further, when the aC:H film is formed after forming the ta-C film that does not contain the protuberant features on the base material, as shown in FIG. C: H film wears abnormally.

In the present embodiment, the ta-C film 2 is made of high-hardness hard carbon with a high proportion of sp ³ in order to ensure wear resistance by the protuberances 3 having the same structure as the ta-C film 2. The aC:H film ⁴ is a low-hardness hard carbon film with a low proportion of sp3.

Specifically, the ta-C film 2 preferably has an ID/IG ratio of 0.2 to 0.8 or a hydrogen content of 15 atom % or less. On the other hand, the hydrogen content of the aC:H film 4 is preferably 20 atom % or more.

Since the height of the bumps 3 is usually about 0.5 μm or less, the aC:H film 4 is preferably formed to have a thickness of 0.1 to 0.5 μm.

(2) Manufacturing method of hard carbon film The hard carbon film according to the present embodiment described above is manufactured according to the following steps.

(a) Preparation of base material First, a base material on which a hard carbon film is to be formed is prepared and set in a film forming tank. At this time, a rare gas such as Ar gas or hydrogen gas is introduced into the film forming tank to generate plasma, and a bias voltage is applied to the base material to prevent contamination and oxidation of the surface of the base material on which the hard carbon film is formed. It is preferred to remove the layer.

It is preferable to previously form a metal film as an intermediate layer on the hard carbon film-forming surface from which dirt and oxide layers have been removed, because the adhesion with the hard carbon film can be improved. This intermediate layer (metal film) can be formed by an arc ion plating method using a metal raw material such as Cr or W as an arc evaporation source.

(b) Preparation of ta-C Film A ta-C film is formed on a base material by arc ion plating using a graphite cathode as an arc evaporation source. At this time, by adjusting the current (arc current) applied to the arc evaporation source and the film thickness of the ta-C film, it is possible to control the density of the bumps.

Normally, in the arc ion plating method, arc discharge is generated on the surface of the arc evaporation source, and carbon is ionized from the graphite cathode and discharged into the deposition tank. At the same time, the impact of the arc discharge damages the graphite. However, fine particles of graphite are frequently discharged into the film forming tank. When the fine particles of graphite adhere to the surface of the ta-C film during formation, the ta-C particles grow in a cone-like shape with the fine particles of graphite as nuclei to form bumps.

At this time, if the arc current is increased, the frequency of breakage of the graphite cathode increases, which promotes the formation of protuberances and forms a ta-C film with a high density of protuberances. In addition, since it is necessary to lengthen the film formation time in order to produce a thick ta-C film, even if the same arc current is used, the number of times the graphite cathode is damaged increases. The amount of graphite microparticles adhering to the surface of the C film increases, and a ta-C film with a high density of raised features is also formed. Finally, the density described above, that is, the number of microprojections on the surface of the hard carbon film is 80 to 300 per 1.25 mm measured length on a straight line extending in the direction along the surface, or the hard carbon film The ta-C film is formed so that the cross section has 8 to 30 protruding features per 125 μm measured length on a straight line extending in the direction along the surface.

In the present embodiment, in order to form the fine particles of graphite, which serve as starting points for the formation of the protuberances, on the surface of the ta-C film with a sufficient density, the ta-C film must be formed with a high arc current. is preferable, and furthermore, in order to form protuberances with a uniform height, it is preferable to form the ta-C film while changing the arc current as follows.

First, a region where the thickness of the ta-C film growing from the surface of the base material becomes 0.3 μm remaining with respect to the design thickness is produced with a predetermined arc current. After that, in the remaining 0.3 to 0.1 μm region, the arc current is set to 40 A or more and higher than in the region before 0.3 μm. Furthermore, in the remaining area of less than 0.1 μm, the arc current is set to more than 0A and 40A or less. At that time, in the remaining 0.3 to 0.1 μm region, it is more preferable to insert a step of re-ignition after extinguishing the arc discharge. As a result, a large amount of graphite fine particles are scattered in the region of 0.3 to 0.1 μm, and a protuberance-like shape having a sufficient density and uniform height can be formed.

(c) Formation of aC:H Film After forming the ta-C film with a predetermined thickness, an aC:H film is formed on the ta-C film.

At this time, an apparatus different from the above-described ta-C film forming apparatus may be used as a film forming apparatus. Since the adhesion of the H film to the ta-C film tends to deteriorate, it is desirable to form the aC:H film continuously after forming the ta-C film using the same apparatus.

In the present embodiment, after the ta-C film is produced by the arc ion plating apparatus, a rare gas such as Ar gas and a hydrocarbon gas are introduced, and a bias voltage is applied to the base material coated with the ta-C film. A self-discharge type CVD discharge is generated by applying the voltage, and an aC:H film is formed on the ta-C film. Other film forming methods include a CVD method using CVD discharge from an external plasma source, a sputtering method in which a graphite cathode is used as a sputtering source, and a rare gas such as Ar gas and a hydrocarbon gas are introduced to form a film. Alternatively, a film formation method that does not generate graphite microparticles during film formation may be used.

There is no problem even if the film thickness of the formed aC:H film is thick. As shown in FIG. 3, it is easily worn out until it becomes scattered like islands with a certain density or more. On the other hand, if it is as thin as less than 0.1 μm, the effect of retaining the bumps formed on the ta-C film cannot be obtained. The height of the bumps formed on the ta-C film is usually about 0.5 μm or less. Considering the above, the film thickness of the aC:H film is preferably 0.1 to 0.5 μm, more preferably 0.2 to 0.3 μm.

In the present embodiment, since the protuberances formed in the lower ta-C film function as pillars to maintain wear resistance, the aC:H film contains Cr, By containing metal elements such as Fe and Si, nitrogen, and boron, even if the hardness of the aC:H film is lowered, the wear resistance is not impaired, and the surface of the hard carbon film is more actively It becomes possible to form a tribofilm on the substrate. Thus, in the present embodiment, the aC:H film may be an aC:H film containing the metal elements described above. The content at this time is preferably 1 to 20 atom %.

(d) Lapping after deposition The coating according to the present invention is formed by coating an aC:H film on a ta-C film, and the aC:H film retains the raised features in the ta-C film. By doing so, the protuberances are prevented from coming off, so that the performance can be fully exhibited even without lapping after film formation.

However, since the protuberant morphology grown starting from the graphite particles attached at the end of the formation of the ta-C film has a weak bond with the ta-C film, even if it is covered with the aC:H film, It falls off more easily than other protuberances. For this reason, although it is very slight, there is a case where the protuberant form falls off.

In order to remove such protuberant forms that have fallen off, the present embodiment may also be subjected to lapping as necessary. In particular, when the sliding partner is a soft material such as copper or aluminum, it is preferable to perform lapping because there is a risk of damaging the mating member even if there is only a small amount of protuberances that have fallen off. .

As a specific lapping method, lapping such as shot blasting in which abrasive grains are hit may be used. In addition to the removal of , the surface can be smoothed by abrading the convex structures on the aC:H film, which is preferable.

Such a lapping process can be applied not only to remove fallen protuberances, but also to intentionally expose protuberances to the surface. In this case, tape wrapping or brush wrapping is particularly preferred.

[1] Characteristic Evaluation of Hard Carbon Film First, an experiment was conducted to evaluate the characteristics of the hard carbon film.

1. Preparation of test body (1) Example 1-1
Using an SCM415 carburized disk (φ31 mm×t3 mm, HRC60, surface roughness Ra<0.01 μm) as a base material, a ta-C film with a thickness of 1.0 μm was formed according to the method for producing a hard carbon film according to the present embodiment described above. and further forming an aC:H film with a thickness of 0.3 μm on the ta-C film, thereby forming a hard carbon film in which the ta-C film and the aC:H film are laminated. A sliding member of Example 1-1 was produced.

Specifically, first, the base material was set on a jig in the film forming apparatus so that the film forming surface faced the graphite cathode, and then the inside of the film forming apparatus was evacuated. Next, while evaporating the graphite cathode by arc discharge, a ta-C film was formed on the surface of the base material without introducing gas from the outside. Subsequently, while introducing acetylene and Ar into the film forming apparatus, a DC pulse voltage was applied to form an aC:H film on the ta-C film by plasma CVD using DC pulse discharge plasma.

(2) Comparative Example 1-1
A ta-C film having a thickness of 1.0 μm was formed on the same base material to prepare a sliding member of Comparative Example 1-1 in which only the ta-C film was a hard carbon film. The film formation was performed in the same manner as the ta-C film of Example 1-1.

(3) Comparative Example 1-2
An aC:H film having a thickness of 1.0 μm was formed on the same base material, and a sliding member of Comparative Example 1-2 having only the aC:H film as a hard carbon film was produced. The plasma CVD method using high-frequency discharge plasma was used. Specifically, first, after setting the base material on a jig in the film forming apparatus, the inside of the film forming tank was evacuated. Next, Ar was introduced, a high frequency bias (frequency of 13.56 MHz) was applied to the Si cathode facing the base material, and a Si film of 0.3 μm was formed by a sputtering method. Subsequently, while introducing methane and Ar into the film-forming apparatus, a high-frequency bias was applied to the base material, and an aC:H film of 1.0 μm was formed by plasma CVD using high-frequency discharge plasma.

2. Evaluation of Film Properties Each hard carbon film formed in Example 1-1 and Comparative Examples 1-1 and 1-2 was evaluated on the following items.

(1) Hydrogen Content The hydrogen content in the hard carbon film formed on each sliding member was measured by the RBS method (Rutherford Backscattering Spectrometry).

As a result, it was found that in Example 1-1, the hydrogen content in the ta-C film was less than the measurement limit of 0.1 atom %, and the hydrogen content in the aC:H film was 26 atom %. On the other hand, in Comparative Example 1-1, the hydrogen content in the ta-C film is less than the measurement limit of 0.1 atom%, and in Comparative Example 1-2, the hydrogen content in the aC:H film is 24 atom%. I found out.

(2) sp ³ /(sp ³ +sp ² ) ratio The hard carbon film has a mixture of sp ² structure and sp ³ structure, and the ratio (sp ³ /(sp ³ +sp ² ) ratio) determines the hard carbon film Specifically, the higher the proportion of sp3 ^, the higher the hardness.

And this sp ³ / (sp ³ + sp ² ) ratio is correlated with the (ID/IG ratio) based on the Raman spectrum as described above, so it can be estimated using a calibration curve from the results of Raman spectrometry. can be done.

Specifically, the Raman spectroscopic measurement was performed by using NRS-5100 manufactured by JASCO Corporation and irradiating laser light with a wavelength of 532 nm. The obtained Raman spectrum was separated into two waveforms, D peak and G peak, which are often used in the analysis of hard carbon films, and analyzed. Specifically, after a straight baseline is drawn between 900 cm ⁻¹ and 1800 cm ⁻¹ and the baseline is set to zero, the D peak centered around 1350 cm ⁻¹ and the vicinity of 1550 cm ⁻¹ Each central G peak was separated by fitting with a Gaussian function, and the area ID of the D peak and the area IG of the G peak were quantified.

Based on the ID/IG area ratio obtained by Raman spectroscopy, the sp ³ /(sp ³ +sp ² ) ratio was obtained using the following empirical formula (Formula 1). This empirical formula was obtained by correlating the results of Raman spectroscopic analysis of various hard carbon films with the results of sp ³ /(sp ³ +sp ² ) ratio analysis by NMR (nuclear magnetic resonance), and found a good correlation. can be used as an equation to estimate the sp ³ /(sp ³ +sp ² ) ratio.
sp ³ /(sp ³ +sp ² ) ratio=55.5X ² -163.9X+142.0 (equation 1)
* X: ID/IG area ratio

As a result, in Example 1-1, the sp ³ /(sp ³ +sp ² ) ratio in the ta-C film was 0.90, and the sp ³ /(sp ³ +sp ² ) ratio in the aC:H film was 0. .39. On the other hand, in Comparative Example 1-1, the sp ³ /(sp ³ +sp ² ) ratio in the ta-C film was 0.90, and in Comparative Example 1-2, the sp ³ /(sp ³ +sp ² ) ratio was found to be 0.43.

(3) Film hardness (nanoindentation hardness)
Nanoindentation hardness was measured as the film hardness of each hard carbon film. Specifically, using an indentation hardness tester ENT-1100a manufactured by Elionix, the nanoindentation hardness was measured with a load of 300 mgf.

As a result, it was found that Example 1-1 was 26 GPa, Comparative Example 1-1 was 55 GPa, and Comparative Example 1-2 was 24 GPa.

(4) Number of Protruding Forms The number of protruding forms in each hard carbon film can be evaluated by measuring the number of fine projections on the surface of the hard carbon film as a peak count value (Pc value). The specific Pc value was measured using Surfcom 480A manufactured by Tokyo Seimitsu Co., Ltd. under the following conditions.

Measurement length: 1.250mm
Measurement speed: 0.06mm/s
Cutoff value: 0.25mm
Filter type: Gaussian Measurement range: ±4.0 μm
Tilt correction: straight line λs value: none Pc upper limit: 0.050 μm
Pc lower limit: 0.000 μm
Probe tip diameter: R2 μm

This Pc value must be measured immediately after the aC:H film is formed. After the production of the aC:H film, if the hard carbon film is lapped or if the surface of the hard carbon film is slid during actual use, the fine protrusions will be worn, so the number of fine protrusions measurement does not allow the number of raised features to be assessed.

In such cases, it is necessary to observe the cross-section of the hard carbon film and directly count the number of raised features. The cross section of the hard carbon film may be cut and polished mechanically, but as shown in the lower SEM image of FIG. (CP) processing and focused ion beam (FIB) processing are more desirable.

In the CP processing and the FIB processing, as shown in the upper part of FIG. 6, the raised features do not fall off, so the number of raised features can be directly counted. On the other hand, in the case of mechanical cutting and polishing, it is necessary to count not only the protuberant features but also the dents from which the protuberant features have fallen off as protuberant features.

As a result of measuring the Pc value immediately after forming the aC:H film, it was 109 in Example 1-1 and 107 in Comparative Example 1-1. It should be noted that Comparative Example 1-2 does not have protuberances because it is produced only by the plasma CVD method.

[2] Evaluation of slidability of sliding member Next, an experiment was conducted to evaluate the slidability of a sliding member having a hard carbon film formed thereon.

1. Preparation of test specimens Next, using an SCM415 carburized material cylinder (φ15 mm × L22 mm, HRC60) as a base material, a hard carbon film of the same thickness was formed by the same method as described above, thereby obtaining Example 2-1 and Sliding members of Comparative Examples 2-1 and 2-2 were produced. In addition, in this experiment, a hard carbon film in which an aC:H film (CN _X film) containing 42 atom % of N was laminated on the ta-C film was formed. No. 2 sliding member was produced.

2. Sliding Test Method A sliding test was performed using each of the produced sliding members with a steel disk (100CR6 (DIN standard)) as a sliding partner.

Specifically, using an SRV (Schwingungs Reihungund und Verschleiss) tester manufactured by Optimol, as shown in FIG. A dynamic test (SRV test) was performed to evaluate sliding characteristics.

In addition, the test conditions at this time are as follows.
・Load: 100N (50N only during pre-breaking)
・Frequency: 33Hz
・Amplitude: 1.5mm
・Time: 120 min (preliminary break-in: 5 min) / 360 min for cross-sectional observation only
・Temperature: 80℃
・Oil: 0W-16 with MoDTC added

3. Test results (a) Surface state and cross-sectional state The surface states of Comparative Example 2-1 and Example 2-1 after 2 hours of the SRV test are shown in the upper part of FIG. A cross-sectional state is shown in the lower part of FIG.

From FIG. 5, in Comparative Example 2-1, although the abrasion was slight, the protuberances fell off, and scratches (abrasive wear) due to the protruded prominences that fell off also occurred in the arrowed parts in the figure. It can be confirmed that there is

In Comparative Example 2-2, it can be confirmed that the aC:H film completely disappeared due to abnormal wear, and the wear progressed to the base material.

On the other hand, in Example 2-1, the aC:H film remained, the protuberances remained without falling off, and it was confirmed that no abrasive wear occurred.

After that, Example 2-1 was further slid, and after a total sliding time of 6 hours, the cross-sectional state was measured. As shown in FIG. It was confirmed that the decrease from time to time was so small that it could not be confirmed at the SEM level.

(b) Coefficient of Friction FIG. 7 shows changes in the coefficient of friction of each sliding member during the sliding test.

As shown in FIG. 7, all of Comparative Example 2-2, Example 2-1, and Example 2-2 exhibit lower coefficients of friction than Comparative Example 2-1.

However, in Comparative Example 2-2, the coefficient of friction increased immediately after starting the test. Therefore, in the MoDTC-containing lubricating oil, even if the aC:H film shows a lower coefficient of friction than the ta-C film, abnormal wear occurs in Comparative Example 2-2, and low friction is stable. It is considered that it is not possible to keep In Comparative Example 2-2, the reason why the coefficient of friction decreased with the lapse of time is considered to be that abnormal wear exposed the steel material as the base material, causing the steel materials to slide against each other.

On the other hand, in Examples 2-1 and 2-2, a low coefficient of friction is maintained, and even in the MoDTC-containing lubricating oil, the slidability is stably superior to that of Comparative Example 2-2. I know it can work.

[3] Evaluation of durability with respect to the number of protruding forms Next, an experiment was conducted to evaluate the durability with respect to the number of protruding forms.

1. Using an SCM415 carburized material cylinder (φ15 mm × L22 mm, HRC60) as a base material, a ta-C film was measured according to the above-described method for producing a hard carbon film according to the present embodiment, and the arc current and The sliding members of Examples 3-1 to 3-3 were produced by forming a thick film and further forming an aC:H film having a thickness of 0.3 μm on the ta-C film. . In addition, Comparative Example 3-1, in which the arc current during the production of the ta-C film was lowered in order to reduce the number of protruding features as much as possible, and the arc current and film thickness were extremely increased in order to increase the number of protruding features as much as possible. Comparative Example 3-2 was produced. Furthermore, Comparative Examples 3-3 and 3-4 were prepared using the filtered arc ion plating method (FVA method) instead of the arc ion plating method (AIP method). Also in Comparative Examples 3-1 to 3-4, an aC:H film having a thickness of 0.3 μm is formed on the ta-C film.

2. Durability Test Method A sliding test was conducted using each of the produced sliding members with a steel disc (100CR6 (DIN standard)) as a sliding partner.

Specifically, using an SRV (Schwingungs Reihungund und Verschleiss) tester manufactured by Optimol, as shown in FIG. A test was conducted to evaluate the sliding properties.

In addition, the test conditions at this time are as follows.
・Load: 100N (50N only during pre-breaking)
・Frequency: 33Hz
・Amplitude: 1.5mm
・Time: 120min (preliminary break-in: 5min)
・Temperature: 80℃
・Oil: 0W-16 with MoDTC added

3. Test Results Table 1 shows the test results.

From Table 1, in Comparative Example 3-1, Comparative Example 3-3, and Comparative Example 3-4 with a small Pc value, the ta-C film was exposed after the durability test, and when the Pc value was small, a protruded form was formed. It can be confirmed that the aC:H film cannot sufficiently exhibit its function as a support for suppressing wear of the H film.

Also in Comparative Example 3-2 with a large Pc value, the ta-C film was exposed after the endurance test, and the protuberances did not exhibit the function of suppressing wear of the aC:H film.

On the other hand, in Examples 3-1 to 3-3, the aC:H film remained even after the endurance test, and in the range of Pc values of 80 to 300, the protuberances did not occur. The function as a support for suppressing wear of the aC:H film can be fully exhibited.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiment within the same and equivalent scope of the present invention.

REFERENCE SIGNS LIST 1 base material 2 ta-C film 3 raised form 4 aC:H film 41 cylinder 42 steel disk

Claims (8)

A hard carbon film coated on the sliding surface of the sliding member,
The first hard carbon film on the lower layer side and the second hard carbon film on the upper layer side are laminated,
The second hard carbon film has a lower hardness than the first hard carbon film,
The first hard carbon film is formed with a plurality of protrusions protruding toward the second hard carbon film,
The second hard carbon film has a thickness of 0.1 to 0.5 μm,
the tip of the raised form is exposed from the surface of the second hard carbon film,
the first hard carbon film is a ta-C film,
the second hard carbon film is an aC:H film,
A hard carbon film, wherein the protruded form has the same structure as the first hard carbon film. The number of microprotrusions derived from the raised morphology formed on the first hard carbon film is 80 per 1.25 mm measured length on a straight line extending in the direction along the surface on the surface of the hard carbon film. 3. The hard carbon film according to claim 1, wherein the number is 300. 8 to 30 protruding features formed on the first hard carbon film per 125 μm measured length on a straight line extending along the surface in the cross section of the hard carbon film. The hard carbon film according to claim 1. The ratio of the area ID of the D peak to the area IG of the G peak obtained from the Raman spectrum of the first hard carbon film (ID/IG ratio) is 0.2 to 0.8. The hard carbon film according to any one of claims 1 to 3. 5. The hard carbon film according to claim 1, wherein the first hard carbon film has a hydrogen content of 15 atom % or less. 6. The hard carbon film according to any one of claims 1 to 5, wherein the second hard carbon film has a hydrogen content of 20 atom % or more. 7. The hard carbon film according to any one of claims 1 to 6 , wherein the second hard carbon film contains 1 to 20 atom % of any one of a metal element, nitrogen, and boron. . A sliding member having a sliding surface coated with the hard carbon film according to any one of claims 1 to 7 , wherein the sliding member slides in MoDTC-containing oil.

Images