JP2013151707A - Sliding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sliding member comprising an Al alloy substrate having a hard carbon coating capable of controlling a friction coefficient, while having improved wear resistance and corrosion resistance and hardly wearing a rubber of another member, in sliding members with rubber, among parts for industrial machines, such as vehicles, which are required to reduce in weight to be more environmentally friendly.SOLUTION: A sliding member includes a base 2 of an aluminum alloy 101 with a surface covered with an oxide film 3. On top of the surface, there is formed a coat 1 which is made up of a conductive layer 4, a buffer layer 5, a graded layer 6, and a diamond-like carbon layer 7 in that order outwardly from the base 2. The diamond-like carbon layer 7 has a surface roughness Ra of 0.15 to 0.5 μm.

Description

  The present invention relates to a sliding member suitable for, for example, a brake piston of an automobile.

  A diamond-like carbon film (DLC film) generally has high hardness, a smooth surface, excellent friction resistance, and excellent low friction performance with a low coefficient of friction due to its solid lubricity. In a non-lubricated environment, the friction coefficient of the surface of a normal smooth steel material is 0.5 or more, and surface friction of conventional surface treatment materials such as Ni-P plating, Cr plating, TiN coating, and CrN coating The coefficient is about 0.4. On the other hand, the coefficient of friction of the DLC film is about 0.1.

  Currently, using these excellent characteristics, it is used in non-lubricated environments such as machining tools such as drill blades, grinding tools, plastic molds, valve cocks and capstan rollers. Application to sliding members and the like. On the other hand, in mechanical parts such as an internal combustion engine in which reduction of mechanical loss as much as possible is desired from the viewpoint of energy consumption and environment, sliding in the presence of lubricating oil is currently the mainstream.

  In addition, automobiles are required to be highly efficient due to environmental considerations, and therefore, it is necessary to reduce the weight of components. For example, a light metal alloy such as an Al alloy is effective for sliding parts for automobiles, and it is essential to improve the performance of sliding parts made of light metal alloys. For example, if a DLC film that is excellent in wear resistance and corrosion resistance, hardly wears a rubber seal, and can control the coefficient of friction with the rubber seal can be formed on the surface of a brake piston made of a light metal alloy, it is highly efficient and reliable. Can provide cars.

  In Patent Document 1, a lubricating oil composition containing an additive having an OH group is mixed in a rubber-like elastic body, and the amount of hydrogen atoms contained on the surface of the inner member or outer member in sliding contact with the rubber-like elastic body is 0. A rubber bush is disclosed in which a hard carbon coating of 5 at% or less is coated, and the inner member or outer member has a surface roughness Rz of 5 μm or less.

  Patent Document 2 discloses a member that sequentially forms a nitrogen-containing chromium coating and a carbon-containing chromium coating on the surface of a base material made of a non-ferrous material such as aluminum or an aluminum alloy, and forms a DLC coating as a hard coating on the carbon-containing chromium coating. Is disclosed.

  However, in the past, when an aluminum alloy brake piston made of an aluminum alloy whose surface was covered with an oxide film was used, rollback (when the hydraulic pressure of the brake was released, the piston was Since the amount of the phenomenon (returned by the elastic deformation amount) increases, there is a problem that feeling during braking is poor. In addition, when using a brake piston for automobiles with a hard carbon coating with a smooth surface, the amount of rollback increases because the rubber seal adsorbs to the piston even in the presence of brake oil and slips poorly. There was a problem that the feeling was bad.

  Also, when steel materials are used for the brake piston for automobiles, the amount of slippage with the rubber seal becomes appropriate by forming a hard carbon coating on the piston, and the weight increases even if the amount of rollback can be controlled appropriately. There was a problem that it was difficult to improve the efficiency of the entire automobile. In addition, when a hard carbon coating for a steel substrate is formed on an Al alloy substrate whose surface is covered with an oxide film (a bond layer, a gradient layer, and a diamond-like carbon layer are formed directly on the oxide film), the oxide film Since this is an electrical insulating layer, a bias voltage cannot be applied in forming the hard carbon film. Therefore, adhesion to the base material of the hard carbon coating is not obtained, and as a result, the amount of rollback increases due to poor sliding with the rubber seal even in the presence of brake oil, so the problem that the feeling during braking is bad there were.

JP 2007-016830 A JP 2009-161813 A

  The object of the present invention is to provide excellent wear resistance and corrosion resistance in a sliding member with rubber among components of industrial equipment such as automobiles that are required to be light in weight for environmental considerations, and it is difficult to wear the rubber of the counterpart material. Another object of the present invention is to provide a sliding member made of an Al alloy base material having a hard carbon film capable of controlling the friction coefficient.

  The sliding member of the present invention is a sliding member in which a conductive layer, a buffer layer, and a diamond-like carbon layer are sequentially arranged on a base material, and the base material is an aluminum alloy covered with an aluminum oxide layer, The buffer layer is a layer that improves adhesion with the base material and supplements the hardness of the base material, and the surface roughness of the diamond-like carbon layer is Ra of 0.15 μm or more and 0.5 μm or less. Features.

  ADVANTAGE OF THE INVENTION According to this invention, the sliding member which has an aluminum alloy as a base material, is excellent in abrasion resistance and corrosion resistance, is hard to wear the rubber | gum of a counterpart material, and has a hard carbon film which can control a friction coefficient can be provided.

It is a figure which shows the cross-section of the base material and hard carbon film which concern on this embodiment. It is sectional explanatory drawing of the friction testing machine used for the friction evaluation of this embodiment. It is a figure which shows the film-forming conditions (Process time vs. target input electric power) in an Example and Comparative Examples 1-2. It is sectional drawing of the brake piston for motor vehicles which shows the Example by this invention.

  The present invention relates to a sliding member having a hard carbon coating that is excellent in wear resistance and corrosion resistance, hardly wears the rubber of a mating member, and can control a friction coefficient.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The hard carbon film shown in the present embodiment can be applied to sliding members (Al alloy base materials) such as machine parts used in a lubricating environment with rubber.

  As shown in FIG. 1, a hard carbon coating (hereinafter referred to as “coating”) 1 can be formed on a substrate 2 by using an unbalanced magnetron sputtering (UBM) method.

  In the UBM method, the balance of the magnetic poles arranged on the back side of the target is intentionally broken at the center and the peripheral part of the target, and a part of the lines of magnetic force from the magnetic poles at the peripheral part of the target is made unbalanced. The amount of ions irradiated onto the substrate 2 during the formation of the coating 1 can be increased by making the plasma that has been extended to the substrate and converging near the target easily diffused to the vicinity of the substrate along the magnetic field lines. As a result, the dense film 1 can be formed on the upper surface side of the substrate 2.

  Although the details will be described with reference to examples, the sliding member of the present invention has a conductive layer 4, the base material 2, and the base material 2 in order from the base material 2, as shown in FIG. It is preferable to form the buffer layer 5 and the diamond-like carbon layer 7 for improving the adhesion of the base material 2 and supplementing the hardness of the substrate 2.

  The conductive layer 4 preferably contains one element selected from aluminum (Al), chromium (Cr), and titanium (Ti).

  The buffer layer 5 preferably contains one kind of nitride selected from chromium nitride and titanium nitride. An inclined layer 6 may be provided between the buffer layer 5 and the diamond-like carbon layer 7.

  When the inclined layer 6 is provided, the inclined layer 6 is a mixture of carbon and metal or a metal carbide, and the content of metal contained in the inclined layer 6 decreases from the substrate 2 side toward the outside. And it is preferable that content of the carbon contained in the said inclination layer 6 increases toward the said outer side from the said base material 2 side. The metal is preferably one element selected from aluminum, chromium and titanium.

The diamond-like carbon layer 7 of the coating used here preferably contains a mixture of sp ² bonded carbon and sp ³ bonded carbon.

  After the coating 1 was formed, the hardness of the surface of the coating 1 was evaluated by a nanoindentation method (ISO14577) and a friction test.

  Hardness evaluation by the nanoindentation method (ISO14577) was performed by pressing a Belkovic triangular pyramid indenter with an opposite edge angle of 115 degrees into the surface of the coating to a maximum load of 3 mN over 10 seconds, holding the maximum load for 1 second, and then over 10 seconds. It was performed under the condition of unloading.

  The hardness of the surface of the coating 1 is preferably 10 GPa or more in order to suppress wear of the diamond-like carbon layer in sliding with the rubber, and is preferably 30 GPa or less in order to suppress wear of the rubber.

  As a friction test evaluation apparatus, a friction coefficient was measured using a reciprocating sliding tester as shown in FIG.

  In this apparatus, a movable work table 12 is arranged, a test piece 11 is installed on the work table 12, and a metal ball having a diameter of 1/2 inch (high carbon chromium bearing steel, A rubber ball 13 in which rubber is wound around a JIS SUJ2 ball) is used as a counterpart material of the test piece 11. Here, the metal used for the metal ball is made of steel used for the bearing. Moreover, although ethylene propylene diene rubber is used for rubber | gum, it is not limited to this.

  In this apparatus, the weights 15 and 16 installed on the shaft 14 are moved so that the load applied to the test piece 11 from the rubber ball 13 is 29.4N.

  At this time, the rubber ball 13 is fixed by the holder 17 so that it does not rotate or come off. Then, the work table 12 is driven with respect to the rubber ball 13 at a maximum sliding speed of 1 mm / sec and a stroke of 10 mm, the friction force generated between the rubber ball 13 and the test piece 11 is measured with a load cell, and the friction coefficient is calculated. did. In addition, this test was carried out under normal temperature and humidity conditions (room temperature: about 25 ° C., humidity: about 60% RH) in a lubrication state using brake oil as a lubricating oil, but the lubricating oil is limited to this. is not.

  As an example, the sliding member is preferably used for an automobile brake piston.

  Examples will be described below.

  FIG. 1 is a cross-sectional view of the sliding member.

  In this figure, the sliding member is formed on the base material 2 whose surface of the aluminum alloy 101 is covered with the oxide film 3, and from the base material 2 side toward the outside, the conductive layer 4, the buffer layer 5, the inclined layer 6 and A coating 1 composed of a diamond-like carbon layer 7 is provided.

  Here, the aluminum alloy 101 is an Al—Mg—Si based alloy A6061-T6 material, and is finished so that the surface roughness Ra of the substrate 2 is 0.15 μm. The coating 1 is formed using the UBM method.

  Specifically, the film 1 is formed under the conditions (process time vs. target input power) shown in FIG.

  First, the conductive layer 4 containing chromium (Cr) as a main component is formed without applying a bias voltage while introducing an inert gas.

  Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of chromium nitride (CrN) is formed while applying a bias voltage.

  Further, the gradient layer 6 is formed while introducing an inert gas and a hydrocarbon gas and applying a bias voltage.

In the formation of the inclined layer 6, first, a chromium carbide layer (chromium carbide layer) is formed, and thereafter, control is performed so that the power input to the chromium target gradually decreases and the power input to the carbon target gradually increases. Here, the chromium carbide constituting the chromium carbide layer, there are types such as _{Cr 3 C 2, Cr 7 C} 3, Cr 23 C 6, but is not limited thereto.

  Finally, an inert gas and a hydrocarbon gas are introduced, and the diamond-like carbon layer 7 is formed while applying a bias voltage.

  The surface roughness Ra of the coating 1 is almost determined by the surface roughness of the substrate 2 before film formation when the coating 1 is thin, but when the coating 1 is thick, the coating 1 has a film thickness Ra. It increases in proportion to. Therefore, the surface roughness Ra of the coating 1 is controlled by the surface roughness of the substrate 2 before film formation and the film thickness of the coating 1.

  The hardness of the diamond-like carbon layer 7 is controlled by adjusting the magnitude of the bias voltage.

  Thereby, first, since the surface of the electrically insulating base material 2 can be changed to conductivity, the buffer layer 5, the inclined layer 6, and the diamond-like carbon layer 7 can be formed.

  In general, the hard carbon coating has better adhesion as the base such as the substrate 2 has a higher hardness. Here, the film 1 refers to a laminated film including the conductive layer 4, the buffer layer 5, the inclined layer 6, and the diamond-like carbon layer 7.

  The buffer layer 5 improves the adhesion between the diamond-like carbon layer 7 and the substrate 2 when the coating 1 is formed on the substrate 2 formed of a soft Al alloy as in this embodiment. The layer for supplementing the hardness of the base material 2 is indicated. The buffer layer 5 is preferably harder than the base material 2. In the present embodiment, the hardness of the base material 2 made of a soft Al alloy can be supplemented by the buffer layer 5 containing CrN, so that the adhesion of the diamond-like carbon layer 7 becomes good.

  In addition, since the inclined layer 6 exists between the buffer layer 5 and the diamond-like carbon layer 7, the adhesion of the diamond-like carbon layer 7 can be further improved.

  Furthermore, since the pinhole in the oxide film 3 on the surface of the substrate 2 can be closed with the coating 1, the corrosion resistance is improved as compared with the case where the substrate 2 is exposed.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  The film 1 of the present example formed as described above had a film thickness of 1.7 μm, a surface roughness Ra of 0.19 μm, a hardness of 23 GPa, and the friction coefficient at this time was 0.28. With this friction coefficient value, the slip amount between the coating 1 and the rubber ball 13 is appropriate. Further, no abrasion was observed on the surface of the coating 1 after the test. Although wear was observed on the surface of the rubber ball 13, the amount of wear was very small.

  As described above, according to this embodiment, it is possible to provide a sliding member that is excellent in wear resistance and corrosion resistance, hardly wears the rubber of the counterpart material, and can control the friction coefficient. Further, when the sliding member of the present invention is applied to an automobile, since the Al alloy is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. Furthermore, when the sliding member of the present embodiment is applied to a brake piston of an automobile, the amount of rollback at the time of braking can be appropriately controlled, so that a brake having a good feeling at the time of braking can be provided. .

In this embodiment, the conductive layer 4 is Cr, the buffer layer 5 is CrN, and the graded layer 6 is Cr carbide. However, the present invention is not limited thereto, and the conductive layer 4 is Ti or Al, the buffer layer 5 is TiN, and graded. The same effect can be obtained even if the layer 6 is made of titanium carbide. Further, the buffer layer 5 may be formed of titanium carbide or Cr carbide (Cr ₃ C ₂ , Cr ₇ C ₃ , Cr ₂₃ C _6, etc.).

In the diamond-like carbon layer 7 in the present embodiment, sp ² bonded carbon, which is a carbon bond typified by graphite, and sp ³ bonded carbon, which is a carbon bond typified by diamond, are mixed. Thereby, the coating film 1 having both wear resistance and corrosion resistance can be provided.
In general, a DLC film is a film formed of amorphous carbon or hydrogenated carbon, and is also called amorphous carbon or hydrogenated amorphous carbon (aC: H).
The DLC film is formed by vapor phase synthesis such as plasma CVD method in which hydrocarbon gas is plasma-decomposed, ion beam evaporation method using carbon / hydrocarbon ions, or graphite is evaporated by arc discharge. An ion plating method for forming a film, a sputtering method for forming a film by sputtering a target in an inert gas atmosphere, and the like are used.

  The coating 1 formed in this embodiment imparts wear resistance and corrosion resistance to the sliding member, makes it difficult to wear the rubber of the mating member, and enables control of the friction coefficient. As a result, an appropriate amount of rubber slips in the presence of brake oil, and neither the coating nor the rubber wears, so that a highly reliable sliding member can be provided.

  In this example, A6061-T6 material is used as the base material 2, but since the age hardening temperature is about 160 to 180 ° C., the temperature during the formation of the coating film 1 is not more than the age hardening temperature. It is necessary to set temperature conditions so as to suppress softening.

  In the formation of the coating 1 of the present invention, the buffer layer 5 containing CrN and the oxide film 3 on the surface of the substrate 2 are formed. In order to improve the adhesion between the substrate 2 and the buffer layer 5, it is preferable to form the conductive layer 4 between the substrate 2 (oxide film 3) and the buffer layer 5.

Further, in the inclined layer 6 formed between the buffer layer 5 and the diamond-like carbon layer 7, first, a Cr carbide layer is formed, and then, from the buffer layer 5 side toward the diamond-like carbon layer 7 side, It is preferable that the Cr concentration decreases continuously and the C concentration increases continuously. Further, when a Cr carbide is a material constituting the gradient layer 6, expressed in Cr _x C _y, by varying the ratio of x and y gradually, diamondlike carbon layer 7 side composition from the buffer layer 5 side It is preferable to change gradually toward.

  As described above, the coating 1 having good adhesion can be provided by designing the structure from the base material 2 to the diamond-like carbon layer 7 as described above. The coating 1 is preferably formed by sputtering or ion plating, in which conditions can be easily set in designing the film as described above.

  A coating 1 shown in FIG. 1 is formed using UBM on a base material 2 in which the surface of an A6061-T6 material of an Al—Mg—Si alloy is covered with an oxide film 3. Further, the substrate 2 is finished so that the surface roughness Ra thereof is 0.25 μm.

  Specifically, the film 1 is formed under the conditions (process time vs. target input power) shown in FIG. First, the conductive layer 4 mainly composed of Cr is formed without introducing a bias voltage while introducing an inert gas. Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while applying a bias voltage. Further, the gradient layer 6 is formed while introducing an inert gas and a hydrocarbon gas and applying a bias voltage. In the formation of the inclined layer 6, first, a Cr carbide layer is formed, and thereafter, control is performed so that the Cr target input power gradually decreases and the carbon target input power gradually increases. Finally, an inert gas and a hydrocarbon gas are introduced, and the diamond-like carbon layer 7 is formed while applying a bias voltage.

Thereby, first, since the surface of the electrically insulating base material 2 can be changed to be conductive, the buffer layer 5, the inclined layer 6 and the diamond-like carbon layer 7 can be formed.
The buffer layer 5 is preferably harder than the base material 2. In the present embodiment, the hardness of the base material 2 made of a soft Al alloy can be supplemented by the buffer layer 5 containing CrN, so that the adhesion of the diamond-like carbon layer 7 becomes good. In addition, since the inclined layer 6 exists between the buffer layer 5 and the diamond-like carbon layer 7, the adhesion of the diamond-like carbon layer 7 can be further improved. Furthermore, since the pinhole in the oxide film 3 on the surface of the substrate 2 can be closed with the coating 1, the corrosion resistance is improved as compared with the case where the substrate 2 is exposed.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  The film 1 of the present example formed as described above had a film thickness of 1.7 μm, a surface roughness Ra of 0.29 μm, a hardness of 23 GPa, and the friction coefficient at this time was 0.21. With this friction coefficient value, the slip amount between the coating 1 and the rubber ball 13 is appropriate. Further, no abrasion was observed on the surface of the coating 1 after the test. Although the surface of the rubber ball 13 was worn, the amount of wear was slight.

  As described above, according to this embodiment, it is possible to provide a sliding member that is excellent in wear resistance and corrosion resistance, hardly wears the rubber of the counterpart material, and can control the friction coefficient. Further, when the sliding member of the present invention is applied to an automobile, since the Al alloy is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. Furthermore, when the sliding member of the present embodiment is applied to a brake piston of an automobile, the amount of rollback at the time of braking can be appropriately controlled, so that a brake having a good feeling at the time of braking can be provided. .

  In this embodiment, the conductive layer 4 is Cr and the buffer layer 5 is CrN. However, the present invention is not limited to these, and the same effect can be obtained when the conductive layer 4 is Al or Ti and the buffer layer 5 is TiN.

  A coating 1 shown in FIG. 1 is formed using UBM on a base material 2 in which the surface of an A6061-T6 material of an Al—Mg—Si alloy is covered with an oxide film 3. Further, the surface roughness Ra of the substrate 2 is finished to be 0.15 μm.

  Specifically, the film 1 is formed under the conditions (process time vs. target input power) shown in FIG. First, the conductive layer 4 mainly composed of Cr is formed without introducing a bias voltage while introducing an inert gas. Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while applying a bias voltage. Further, the gradient layer 6 is formed while introducing an inert gas and a hydrocarbon gas and applying a bias voltage. In the formation of the inclined layer 6, first, a Cr carbide layer is formed, and thereafter, control is performed so that the Cr target input power gradually decreases and the carbon target input power gradually increases. Finally, an inert gas and a hydrocarbon gas are introduced, and the diamond-like carbon layer 7 is formed while applying a bias voltage.

  Thereby, first, since the surface of the electrically insulating base material 2 can be changed to be conductive, the buffer layer 5, the inclined layer 6 and the diamond-like carbon layer 7 can be formed. The buffer layer 5 is preferably harder than the base material 2. In the present embodiment, the hardness of the base material 2 made of a soft Al alloy can be supplemented by the buffer layer 5 containing CrN, so that the adhesion of the diamond-like carbon layer 7 becomes good. In addition, since the inclined layer 6 exists between the buffer layer 5 and the diamond-like carbon layer 7, the adhesion of the diamond-like carbon layer 7 can be further improved. Furthermore, since the pinhole in the oxide film 3 on the surface of the substrate 2 can be closed with the coating 1, the corrosion resistance is improved as compared with the case where the substrate 2 is exposed.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  The film 1 of the present example formed as described above had a film thickness of 8.1 μm, a surface roughness Ra of 0.50 μm and a hardness of 30 GPa, and the friction coefficient at this time was 0.18. With this friction coefficient value, the slip amount between the coating 1 and the rubber ball 13 is appropriate. Further, no abrasion was observed on the surface of the coating 1 after the test. Although the surface of the rubber ball 13 was worn, the amount of wear was slight.

  As described above, according to this embodiment, it is possible to provide a sliding member that is excellent in wear resistance and corrosion resistance, hardly wears the rubber of the counterpart material, and can control the friction coefficient. Further, when the sliding member of the present invention is applied to an automobile, since the Al alloy is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. Furthermore, when the sliding member of the present embodiment is applied to a brake piston of an automobile, the amount of rollback at the time of braking can be appropriately controlled, so that a brake having a good feeling at the time of braking can be provided. .

  In this embodiment, the conductive layer 4 is Cr and the buffer layer 5 is CrN. However, the present invention is not limited to these, and the same effect can be obtained when the conductive layer 4 is Al or Ti and the buffer layer 5 is TiN.

  FIG. 4 is a sectional view of an automobile brake piston showing an embodiment according to the present invention.

  The brake piston in this figure is for a two-wheeled vehicle, and the brake is operated by sandwiching the disc rotor 22 rotating coaxially with the wheels from the left and right with the inner brake pad 26 of the two stages of brake pads 24, 26, The wheel stops rotating. This figure is a longitudinal sectional view seen from a direction parallel to the rotation direction of the wheel and the disk rotor 22, and the rotation direction of the disk rotor 22 is a direction perpendicular to the paper surface.

  In this figure, a piston 23, brake pads 24 and 26, and a seal 25 are accommodated inside a cylinder bore 21. The seal 25 is installed between the cylinder bore 21 and the piston 23 so that the brake oil 203 sealed in the cylinder bore 21 does not leak. When the pressure of the brake oil 203 is applied to the left and right pistons 23, the left and right pistons 23 are moved inward so that the brake pads 26 and the disc rotor 22 are brought into contact with each other.

[Comparative Example 1]
A coating 1 shown in FIG. 1 is formed using UBM on a base material 2 in which the surface of an A6061-T6 material of an Al—Mg—Si alloy is covered with an oxide film 3. Further, the surface roughness Ra of the substrate 2 is finished to 0.02 μm.

  Specifically, the film 1 is formed under the conditions (process time vs. target input power) shown in FIG. First, the conductive layer 4 mainly composed of Cr is formed without introducing a bias voltage while introducing an inert gas. Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while applying a bias voltage. Further, the gradient layer 6 is formed while introducing an inert gas and a hydrocarbon gas and applying a bias voltage. In the formation of the inclined layer 6, first, a Cr carbide layer is formed, and thereafter, control is performed so that the Cr target input power gradually decreases and the carbon target input power gradually increases. Finally, an inert gas and a hydrocarbon gas are introduced, and the diamond-like carbon layer 7 is formed while applying a bias voltage.

Thereby, first, since the surface of the electrically insulating base material 2 can be changed to be conductive, the buffer layer 5, the inclined layer 6 and the diamond-like carbon layer 7 can be formed.
The buffer layer 5 is preferably harder than the base material 2. In this comparative example, since the hardness of the base material 2 made of a soft Al alloy can be supplemented by the buffer layer 5 containing CrN, the adhesion of the diamond-like carbon layer 7 becomes good. In addition, since the inclined layer 6 exists between the buffer layer 5 and the diamond-like carbon layer 7, the adhesion of the diamond-like carbon layer 7 can be further improved. Furthermore, since the pinhole in the oxide film 3 on the surface of the substrate 2 can be closed with the coating 1, the corrosion resistance is improved as compared with the case where the substrate 2 is exposed.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  The film 1 of this comparative example formed with the above structure had a film thickness of 1.7 μm, a surface roughness Ra of 0.10 μm and a hardness of 23 GPa, and the friction coefficient at this time was as high as 0.39. No abrasion was observed on the surface of the coating 1 after the test. On the other hand, large wear marks were observed on the surface of the rubber ball 13.

  As described above, the sliding member of this comparative example is excellent in wear resistance and corrosion resistance, but wears the rubber of the mating member and cannot control the friction coefficient. When the sliding member of this comparative example is applied to an automobile, since the Al alloy is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. When applied to a brake piston, the amount of rollback at the time of braking increases, so that it is not possible to provide a brake with a good feeling at the time of braking.

[Comparative Example 2]
A coating 1 shown in FIG. 1 is formed using UBM on a base material 2 in which the surface of an A6061-T6 material of an Al—Mg—Si alloy is covered with an oxide film 3. Further, the surface roughness Ra of the substrate 2 is finished to be 0.15 μm.

  Specifically, the film 1 is formed under the conditions (process time vs. target input power) shown in FIG. First, the conductive layer 4 mainly composed of Cr is formed without introducing a bias voltage while introducing an inert gas. Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while applying a bias voltage. Further, the gradient layer 6 is formed while introducing an inert gas and a hydrocarbon gas and applying a bias voltage. In the formation of the inclined layer 6, first, a Cr carbide layer is formed, and thereafter, control is performed so that the Cr target input power gradually decreases and the carbon target input power gradually increases. Finally, an inert gas and a hydrocarbon gas are introduced, and the diamond-like carbon layer 7 is formed while applying a bias voltage.

Thereby, first, since the surface of the electrically insulating base material 2 can be changed to be conductive, the buffer layer 5, the inclined layer 6 and the diamond-like carbon layer 7 can be formed.
The buffer layer 5 is preferably harder than the base material 2. In this comparative example, since the hardness of the base material 2 made of a soft Al alloy can be supplemented by the buffer layer 5 containing CrN, the adhesion of the diamond-like carbon layer 7 becomes good. In addition, since the inclined layer 6 exists between the buffer layer 5 and the diamond-like carbon layer 7, the adhesion of the diamond-like carbon layer 7 can be further improved. Furthermore, since the pinhole in the oxide film 3 on the surface of the substrate 2 can be closed with the coating 1, the corrosion resistance is improved as compared with the case where the substrate 2 is exposed.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  The film 1 of this comparative example formed with the above structure had a film thickness of 1.8 μm, a surface roughness Ra of 0.24 μm, a hardness of 9 GPa, and the friction coefficient at this time was 0.24. Although the surface of the rubber ball 13 was worn, the amount of wear was slight. On the other hand, wear was observed on the surface of the coating 1 after the test.

  As described above, the sliding member of this comparative example is excellent in corrosion resistance, hardly wears the counterpart rubber, and can control the coefficient of friction, but has poor wear resistance. When the sliding member of this comparative example is applied to an automobile, since the Al alloy is used for the substrate 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. However, when applied to a brake piston of an automobile, the coating 1 on the piston is worn away by long-term use, so that the base material 2 is exposed and the seal 25 and the piston 23 are easily slipped. As a result, the amount of rollback at the time of braking is reduced, so that the piston does not return to the initial position when the brake is released, and the disc rotor 22 and the brake pad 24 are dragged, and a reliable brake cannot be provided. .

[Comparative Example 3]
The surface of the A6061-T6 material of Al—Mg—Si alloy is used without forming the coating 1 on the base material 2 covered with the oxide film 3. Further, the surface roughness Ra of the substrate 2 is finished to 0.02 μm.

  Thereby, since there is no film which closes the pinhole in the oxide film 3 on the surface of the substrate 2, the corrosion resistance is low.

  In the friction test evaluation, ethylene propylene diene rubber was used for the rubber ball 13 of the counterpart material, and brake oil was used for the lubricating oil 202.

  In this comparative example formed with the above configuration, the friction coefficient was as low as 0.13. Abrasion scratches were observed on the surface of the base material 2 after the test. Although the surface of the rubber ball 13 was worn, the amount of wear was slight. Moreover, the transfer of the abrasion powder of the base material 2 was observed on the surface of the rubber ball 13. With this friction coefficient value, the slip amount of the rubber ball 13 with the coating 1 is excessive.

  As described above, the sliding member of this comparative example hardly wears the rubber of the mating member, but is inferior in wear resistance and corrosion resistance and cannot control the coefficient of friction. When the sliding member of this comparative example is applied to an automobile, since the Al alloy is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a highly efficient automobile can be provided. When applied to a brake piston, the brake piston first wears, and the amount of rollback during braking is reduced, so that the piston does not return to the initial position when braking is released, and the disc rotor 22 and the brake pad 24 drag. . As a result, a reliable brake cannot be provided.

DESCRIPTION OF SYMBOLS 1 Hard carbon film 2 Base material 3 Oxide film 4 Conductive layer 5 Buffer layer 6 Inclined layer 7 Diamond-like carbon layer 11 Test piece 12 Work table 13 Rubber ball 14 Shaft 15, 16 Weight 17 Holder 21 Cylinder bore 22 Disc rotor 23 Piston 24 Brake Pad 25 Seal 26 Brake pad 101 Aluminum alloy 202 Lubricating oil 203 Brake oil

Claims (10)

A sliding member in which a conductive layer, a buffer layer, and a diamond-like carbon layer are sequentially arranged on a base material,
The base material is an aluminum alloy covered with an aluminum oxide layer;
The buffer layer is a layer that improves adhesion with the substrate and supplements the hardness of the substrate,
The surface roughness of the diamond-like carbon layer is 0.15 μm or more and 0.5 μm or less in terms of Ra.   The sliding member according to claim 1, wherein the conductive layer contains at least one selected from aluminum, chromium, and titanium.   The sliding member according to claim 1 or 2, wherein the buffer layer contains at least one selected from chromium nitride and titanium nitride.   The sliding member according to claim 1 or 2, wherein the buffer layer contains at least one selected from chromium carbide and titanium carbide.   The sliding member according to any one of claims 1 to 4, wherein an inclined layer is provided between the buffer layer and the diamond-like carbon layer.   The gradient layer is a mixture of carbon and metal or a metal carbide, and the content of metal contained in the gradient layer decreases from the substrate side toward the outside, and the content of carbon contained in the gradient layer. 6. The sliding member according to claim 5, wherein the amount increases from the substrate side toward the outside, and the metal is at least one selected from aluminum, chromium, and titanium.   7. The sliding member according to claim 1, wherein the diamond-like carbon layer has a surface hardness of 10 GPa or more and 30 GPa or less. The sliding member according to any one of claims 1 to 7, wherein the diamond-like carbon layer contains sp ² bonded carbon and sp ³ bonded carbon.   A brake piston for an automobile, comprising the sliding member according to any one of claims 1 to 8. Forming a conductive layer by sputtering or ion plating on the surface of an aluminum alloy covered with an aluminum oxide layer; and
In a state where a bias voltage is applied to the base material, the step of improving the adhesion with the base material on the conductive layer and forming a buffer layer for supplementing the hardness of the base material;
Forming a gradient layer on the buffer layer;
Forming a diamond-like carbon layer having a surface roughness Ra of 0.15 μm or more and 0.5 μm or less on the inclined layer;
The manufacturing method of the sliding member characterized by including.

Images