WO2011125375A1

WO2011125375A1 - Sliding member

Info

Publication number: WO2011125375A1
Application number: PCT/JP2011/053632
Authority: WO
Inventors: 岡本　晋哉; 昌一中島; 岡本　和孝
Original assignee: 株式会社日立製作所
Priority date: 2010-04-01
Filing date: 2011-02-21
Publication date: 2011-10-13
Also published as: JP2013151707A

Abstract

Among parts for industrial machines, such as automobiles, which are required to reduce in weight to be more environmentally friendly, there are sliding members which are brought into contact with resilient plastic members such as of rubber. Disclosed is a sliding member which has improved wear resistance and corrosion resistance as well as a reduced friction coefficient against the resilient plastic member in contact therewith. The 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 0.5μm which is determined by calculation in conformity with JIS B 0601.

Description

Sliding member

The present invention relates to a sliding member.

A diamond-like carbon film (DLC film) generally has a 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 normal smooth steel surface is 0.5 or more, and the 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 friction coefficient of the DLC film is about 0.1.

Taking advantage of these excellent properties, machining tools such as drill blades, grinding tools, etc., metal molds for plastic working, slides used in non-lubricated environments such as valve cocks and capstan rollers. Application to moving members and the like is attempted. 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. Therefore, it is necessary to reduce the weight of the component parts. For example, a light metal alloy such as an Al alloy is also effective for sliding parts for automobiles.

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 content of hydrogen atoms on the surface of the inner member or outer member in sliding contact with the rubber-like elastic body is 0. 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 hard material in which a nitrogen-containing chromium film and a carbon-containing chromium film are sequentially formed on the surface of a base material made of a non-ferrous material such as aluminum or an aluminum alloy, and a DLC film is formed as a hard film on the carbon-containing chromium film. A film covering member is disclosed.

JP 2007-016830 A JP 2009-161813 A

Conventionally, when an automotive brake piston made of an Al alloy whose surface is covered with an oxide film is used, slipping with the rubber seal is poor even in the presence of brake oil. There is a problem that the amount of the phenomenon (returned by the deformation) is increased and the feeling during braking is poor. In addition, when an automobile brake piston covered with a hard carbon coating with a smooth surface is used, the rubber seal is attracted to the piston even in the presence of brake oil, causing slippage. There was a problem that the feeling was bad.

Also, when steel materials are used for automobile brake pistons, even if the amount of sliding with the rubber seal can be made appropriate by forming a hard carbon coating on the piston and the amount of rollback can be controlled appropriately, the weight is large. Therefore, there is a problem that it is 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 surface of the oxide film) Since the film is an electrically insulating layer, a bias voltage cannot be applied in forming the hard carbon film. For this reason, the adhesion of the hard carbon coating to the substrate was not obtained. As a result, slippage with the rubber seal is deteriorated even in the presence of brake oil, and the amount of rollback is increased.

An object of the present invention is to improve wear resistance and corrosion resistance of a sliding member that comes into contact with an elastic resin member such as rubber among parts of industrial equipment such as automobiles that are required to be reduced in weight for environmental considerations. It is to reduce the coefficient of friction with the elastic resin member in contact.

In the present invention, a material in which a conductive layer, a buffer layer, and a diamond-like carbon layer are formed in this order from the substrate side on the surface of a substrate that is an aluminum alloy covered with an aluminum oxide layer is used as a sliding member. The surface roughness Ra of the diamond-like carbon layer is 0.15 to 0.5 μm.

According to the present invention, the wear resistance and corrosion resistance of the sliding member can be improved, the coefficient of friction with the elastic resin member in contact can be reduced, and the elastic resin member can be made hard to wear.

It is a fragmentary sectional view which shows the structure of the sliding member of an Example. It is principal part sectional drawing of the friction test apparatus used for the friction evaluation of the sliding member of an Example. 5 is a graph showing film forming conditions in Examples 1 and 2 and Comparative Example 1. 6 is a graph showing film forming conditions in Example 3. 10 is a graph showing film forming conditions in Comparative Example 2. It is sectional drawing which shows the brake piston for motor vehicles of an Example.

The hard carbon coating can be applied to a sliding member formed of an aluminum alloy (Al alloy) such as a machine part used in a lubrication environment with rubber.

Improvement of the performance of sliding parts made of light metal alloys such as Al alloys is an important issue. For example, if a DLC film that is excellent in wear resistance and corrosion resistance, hardly wears off the rubber seal, and can control the friction coefficient with the rubber seal can be formed on the surface of the brake piston made of light metal alloy, the efficiency is high and the reliability is high. High cars can be provided.

As a result of intensive studies, the present inventor has developed a hard carbon coating that is excellent in wear resistance and corrosion resistance and that can control (reduce) the friction coefficient so as to make the elastic resin member such as rubber difficult to wear. Developed technology for forming aluminum alloy and other materials.

Hereinafter, a sliding member which is an embodiment of the present invention, an automobile brake piston using the sliding member, and a manufacturing method of the sliding member will be described.

The sliding member is formed by sequentially laminating a conductive layer, a buffer layer, and a diamond-like carbon layer on the surface of a base material. The base material includes an aluminum alloy and an aluminum oxide layer covering the aluminum alloy. The buffer layer is a layer that improves adhesion to the substrate and supplements the hardness of the substrate. The surface roughness Ra of the diamond-like carbon layer calculated in accordance with JIS B 0601 is 0.15 to 0.5 μm.

In the sliding member, an inclined layer is provided between the buffer layer and the diamond-like carbon layer.

The graded layer is a mixture of carbon and metal or a metal carbide, and the metal content contained in the graded layer decreases from the substrate side toward the outside, and the carbon content contained in the graded layer is: The metal increases from the substrate side toward the outside, and the metal is at least one selected from the group consisting of aluminum, chromium and titanium.

In the sliding member, the surface hardness of the diamond-like carbon layer is 10 to 30 GPa.

The manufacturing method of the sliding member includes a step of forming a conductive layer by sputtering or ion plating on the surface of an aluminum alloy covered with an aluminum oxide layer and applying a bias voltage to the substrate. In this state, while improving the adhesion with the substrate on the surface of the conductive layer, forming a buffer layer to supplement the hardness of the substrate, forming a gradient layer on the surface of the buffer layer, Forming a diamond-like carbon layer having a surface roughness Ra of 0.15 to 0.5 μm calculated on the surface of the inclined layer in accordance with JIS B 0601.

Here, the bias voltage refers to a voltage applied to the substrate on which the film is formed. Specifically, the voltage is applied to the base material to attract the sputtered particles generated by sputtering of the target to the base material. The hardness and density of the coating changes depending on the level of the bias voltage.

Also, the target input power is the power input to the target when sputtering the target. The film formation rate (film thickness) changes depending on the magnitude of this electric power.

Hereinafter, an outline of the embodiment will be described with reference to the drawings.

FIG. 1 is a partial cross-sectional view showing an example of the structure of a sliding member.

The sliding member 10 shown in this figure has a coating 1 (hard carbon coating) formed on the surface of the substrate 2 by using unbalanced magnetron sputtering (UBMS method).

Here, the UBMS method intentionally breaks the balance of the magnetic poles arranged on the back side of the target at the center and the peripheral part of the target and makes it non-equilibrium. This is a film forming method in which a part of the plasma extends to the substrate and the plasma that has converged in the vicinity of the target easily diffuses to the vicinity of the substrate along the lines of magnetic force. Therefore, it is possible to increase the amount of ions irradiated on the base material 2 during the formation of the coating film 1 shown in the figure, and as a result, the dense coating film 1 can be formed on the upper surface side of the base material 2.

In this figure, the buffer layer 5 which improves the adhesiveness with the base material 2 in order from the base material 2 side to the base material 2 which formed the oxide film 3 (aluminum oxide layer) on the surface of the aluminum alloy 101 in order. And a diamond-like carbon layer 7 that supplements the hardness of the substrate 2 is formed. It is preferable to provide an inclined layer 6 between the buffer layer 5 and the diamond-like carbon layer 7 as shown in the figure.

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. Here, the content of the metal contained in the inclined layer 6 is configured to decrease from the substrate 2 side toward the outside. On the other hand, the carbon content contained in the inclined layer 6 is configured to increase from the substrate 2 side toward the outside. The metal is preferably one element selected from aluminum, chromium and titanium.

The diamond-like carbon layer 7 of the coating 1 preferably contains a mixture of sp ² bonded carbon and sp ³ bonded carbon.

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

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

The surface hardness 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 preferably 30 GPa or less in order to suppress wear of the rubber.

FIG. 2 shows a reciprocating sliding tester (friction test device) for measuring the friction coefficient.

The friction test apparatus shown in this figure includes a movable work table 12 and a shaft 14 having a holder 18. A vise 17 is installed on the upper surface of the work table 12, and the test piece 11 can be sandwiched and fixed by the vice 17. A ball 13 is installed below the holder 18, and the ball 13 and the test piece 11 installed on the work table 12 are arranged to contact each other. The ball 13 is a metal ball (made of high carbon chromium bearing steel, JIS SUJ2 ball) having a diameter of 1/2 inch wound with rubber. Brake oil is applied as a lubricating oil 202 between the test piece 11 and the ball 13. The ball 13 is fixed by a holder 18 so that it does not rotate or come off.

Weights

15 and 16 are installed on the shaft 14 so that the load applied from the ball 13 to the test piece 11 can be adjusted. The metal used for the metal ball is steel used for the bearing, and the rubber is ethylene propylene diene rubber, but the material is not limited to these.

The friction test was performed in a lubricating state using a lubricating oil 202 in a normal temperature and humidity environment (room temperature: about 25 ° C., humidity: about 60% RH). By moving the

weights

15 and 16 installed on the shaft 14, the load applied to the test piece 11 from the rubber ball 13 was adjusted to 29.4 N.

The work table 12 was driven with respect to the ball 13 at a maximum sliding speed of 1 mm / sec and a stroke of 10 mm. Under the present circumstances, the frictional force which generate | occur | produces between the ball | bowl 13 and the test piece 11 was measured using the load cell, and the friction coefficient was computed. In addition, although the brake oil was used as the lubricating oil 202, it is not limited to this.

The sliding member is preferably used for a brake piston for automobiles as an example.

Hereinafter, examples will be described.

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

In this figure, the sliding member 10 has a conductive layer 4, a buffer layer 5, an inclined layer 6, and a substrate 2 with the surface of an aluminum alloy 101 covered with an oxide film 3, outward from the substrate 2 side. A coating 1 formed of a diamond-like carbon layer 7 is provided.

Here, the aluminum alloy 101 is an Al—Mg—Si based alloy A6061-T6 material. Further, the surface roughness Ra of the substrate 2 is finished to be 0.15 μm. The coating 1 is formed using the UBMS method. Here, the surface roughness Ra is an arithmetic average roughness, which is calculated in accordance with JIS B 0601.

Specifically, the film 1 was formed under the conditions shown in FIG. 3A. The horizontal axis represents the film formation time, and the vertical axis represents the target input power and bias voltage.

In this figure, first, for 4 minutes after the start of film formation, the conductive layer 4 containing chromium (Cr) as a main component is formed without applying a bias voltage while introducing an inert gas. In this step, the chromium target input power is 1.5 kW, and the carbon target input power is 0 kW.

Thereafter, until 44 minutes have elapsed from the start of film formation, 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 of 150V. Also in this step, the chromium target input power is 1.5 kW, and the carbon target input power is 0 kW.

Further, an inert gas and a hydrocarbon gas are introduced until 70 minutes have elapsed from the start of film formation, and the gradient layer 6 is formed while applying a bias voltage of 50V.

In the formation of the inclined layer 6, first, a chromium carbide layer (chromium carbide layer) is formed, and thereafter, control is performed such 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 until 130 minutes have elapsed from the start of film formation, and the diamond-like carbon layer 7 is formed while applying a bias voltage. In the step of forming the diamond-like carbon layer 7, the bias voltage is set to the same value (50 V) as the bias voltage in the step of forming the previous inclined layer until 72 minutes have elapsed since the start of film formation. Thereafter, the bias voltage is gradually increased, and after 88 minutes from the start of film formation, the bias voltage is maintained at a constant value (100 V). In this step, the chromium target input power is 0 kW, and the carbon target input power is 3.0 kW.

Thereby, a dense diamond-like carbon layer 7 is formed, and a surface layer of the coating film 1 having a high hardness can be formed.

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.

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

By using the UBMS method, the conductive layer 4 can be formed on the surface of the insulating base material 2 for the oxide film 3, so that the buffer layer 5, the inclined layer 6, and the diamond-like carbon layer 7 are formed. Is possible.

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

In addition, the buffer layer 5 improves the adhesion between the diamond-like carbon layer 7 and the base material 2 when the coating 1 is formed on the surface of the base material 2 formed of the soft aluminum alloy 101 as in this embodiment. And has a function of supplementing the hardness of the substrate 2. The buffer layer 5 is preferably harder than the base material 2. In this embodiment, since the hardness of the substrate 2 made of the soft aluminum alloy 101 can be supplemented by the buffer layer 5 containing CrN, the adhesion of the diamond-like carbon layer 7 is improved.

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

In this example, the thickness of the coating 1 was 1.7 μm, the surface roughness Ra was 0.19 μm, and the hardness was 23 GPa. And the friction coefficient computed by the friction test was 0.28. This value of the friction coefficient is appropriate as the amount of slip between the coating 1 and the ball 13. Moreover, no abrasion was observed on the surface of the coating 1 after the friction test. Although the surface of the ball 13 was worn, the amount of wear was very small.

As described above, the sliding member of this example is excellent in wear resistance and corrosion resistance, hardly wears the rubber of the mating member, and can control the friction coefficient. Further, when the sliding member of this embodiment is applied to an automobile, since the aluminum alloy 101 is used as the base material 2, the entire automobile can be reduced in weight, and as a result, a fuel-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 gradient layer 6 is Cr carbide. However, the present invention is not limited to these. The same effect can be obtained when the conductive layer 4 is Ti or Al, the buffer layer 5 is TiN, and the inclined layer 6 is 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 this 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.

Generally, the diamond-like carbon layer 7 (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 can be formed by plasma-depositing a hydrocarbon gas by plasma decomposition, a gas-phase synthesis method such as ion beam evaporation using carbon / hydrocarbon ions, or evaporating graphite 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, or the like is used.

The coating film 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 set to be equal to or lower than the age hardening temperature. It is necessary to set the temperature condition so as to suppress the softening.

In the formation of the coating film 1 of the present embodiment, 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.

When the inclined layer 6 is 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. Thus, it is preferable to form the film so 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, diamond-like carbon layer composition from the side of the buffer layer 5 7 It is preferable to change gradually toward the side.

As described above, the coating 1 having high adhesion can be formed by designing the structure from the base material 2 to the diamond-like carbon layer 7 as described above. In addition, the coating 1 is preferably formed by sputtering or ion plating which allows easy setting of conditions for designing the film as described above.

The configuration of the sliding member 10 is the same as that of the first embodiment, as shown in FIG.

The substrate 2 is composed of an aluminum alloy 101 and an oxide film 3 covering the surface thereof. The aluminum alloy 101 is made of an A6061-T6 material of an Al—Mg—Si alloy. The coating 1 is formed on the surface of the oxide film 3 using the UBMS method. The coating 1 is formed of a conductive layer 4, a buffer layer 5, an inclined layer 6, and a diamond-like carbon layer 7 from the substrate 2 side toward the outside. The surface roughness Ra of the coating 1 is finished to be 0.25 μm.

Specifically, the coating 1 was formed under the conditions shown in FIG. The horizontal axis represents the film formation time, and the vertical axis represents the target input power and bias voltage.

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

Thereafter, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while a bias voltage is applied.

Further, an inclined gas 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 (chromium carbide layer) is formed, and thereafter, the Cr target input power is gradually decreased and the carbon target input power is gradually increased.

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 buffer layer 5 is preferably harder than the substrate 2. In this embodiment, since the hardness of the substrate 2 made of the soft aluminum alloy 101 can be supplemented by the buffer layer 5 containing CrN, the adhesion of the diamond-like carbon layer 7 is improved. 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 this example, the film 1 had a thickness of 1.7 μm, a surface roughness Ra of 0.29 μm, and a hardness of 23 GPa. And the friction coefficient computed by the friction test was 0.21. This value of the friction coefficient is appropriate as the amount of slip between the coating 1 and the ball 13. Moreover, no abrasion was observed on the surface of the coating 1 after the friction test. Although wear was observed on the surface of the ball 13, the amount of wear was slight.

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. .

The substrate 2 is composed of an aluminum alloy 101 and an oxide film 3 covering the surface thereof. The aluminum alloy 101 is made of an A6061-T6 material of an Al—Mg—Si alloy. The coating 1 is formed on the surface of the oxide film 3 using the UBMS method. The coating 1 is formed of a conductive layer 4, a buffer layer 5, an inclined layer 6, and a diamond-like carbon layer 7 from the substrate 2 side toward the outside. The surface roughness Ra of the coating 1 is finished to be 0.15 μm.

Specifically, the film 1 was formed under the conditions shown in FIG. 3B. The horizontal axis represents the film formation time, and the vertical axis represents the target input power and bias voltage.

In this drawing, first, for 4 minutes after the start of film formation, the conductive layer 4 containing Cr as a main component is formed without applying a bias voltage while introducing an inert gas. In this step, the chromium target input power is 1.5 kW, and the carbon target input power is 0 kW.

Thereafter, until 44 minutes have elapsed from the start of film formation, an inert gas and a nitrogen gas are introduced, and a buffer layer 5 mainly composed of CrN is formed while a bias voltage of 150 V is applied. Also in this step, the chromium target input power is 1.5 kW, and the carbon target input power is 0 kW.

Further, an inert gas and a hydrocarbon gas are introduced until 172 minutes have elapsed from the start of film formation, and the gradient layer 6 is formed while applying a bias voltage of 50V.

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 a diamond-like carbon layer 7 is formed while applying a bias voltage until 1400 minutes have elapsed since the start of film formation. In the step of forming the diamond-like carbon layer 7, the bias voltage is set to the same value (50 V) as the bias voltage in the step of forming the previous inclined layer until 180 minutes have elapsed since the start of film formation. Thereafter, the bias voltage is gradually increased, and after 500 minutes have elapsed from the start of film formation, the bias voltage is maintained at a constant value (250 V). In this step, the chromium target input power is 0 kW, and the carbon target input power is 3.0 kW.

In this example, the thickness of the coating 1 was 8.1 μm, the surface roughness Ra was 0.50 μm, and the hardness was 30 GPa. And the friction coefficient computed by the friction test was 0.18. This value of the friction coefficient is appropriate as the amount of slip between the coating 1 and the ball 13. Moreover, no abrasion was observed on the surface of the coating 1 after the friction test. Although wear was observed on the surface of the ball 13, the amount of wear was slight.

As described above, the sliding member of this example is excellent in wear resistance and corrosion resistance, hardly wears the rubber of the mating member, and can control the friction coefficient. Moreover, when the sliding member of an Example is applied to a motor vehicle, since the aluminum alloy 101 is used for the base material 2, it can reduce in weight as the whole motor vehicle, As a result, a low fuel consumption motor vehicle 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. .

FIG. 4 is a cross-sectional view showing an automobile brake piston according to an embodiment.

The brake piston in this figure is for a motorcycle, 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 in the cylinder bore 21. The seal 25 is installed between the cylinder bore 21 and the piston 23 so as to prevent the brake oil 203 enclosed in the cylinder bore 21 from leaking out. By transmitting the pressure of the brake oil 203 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 come into contact with each other.

[Comparative Example 1]
The basic configuration of the sliding member 10 is the same as that of the first embodiment, as shown in FIG.

The substrate 2 is composed of an aluminum alloy 101 and an oxide film 3 covering the surface thereof. The aluminum alloy 101 is made of an A6061-T6 material of an Al—Mg—Si alloy. The coating 1 is formed on the surface of the oxide film 3 using the UBMS method. The coating 1 is formed of a conductive layer 4, a buffer layer 5, an inclined layer 6, and a diamond-like carbon layer 7 from the substrate 2 side toward the outside. The surface roughness Ra of the coating 1 is finished to 0.02 μm.

The buffer layer 5 is preferably harder than the substrate 2. In this comparative example, the hardness of the base material 2 made of the soft aluminum alloy 101 can be supplemented by the buffer layer 5 containing CrN, so that the adhesion of the diamond-like carbon layer 7 is improved. 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 this comparative example, the thickness of the coating 1 was 1.7 μm, the surface roughness Ra was 0.10 μm, and the hardness was 23 GPa. The friction coefficient calculated by the friction test was as high as 0.39. No abrasion was observed on the surface of the coating 1 after the friction test. On the other hand, large wear marks were observed on the surface of the 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 does not reduce the friction coefficient. When the sliding member of this comparative example is applied to an automobile, since the aluminum alloy 101 is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a fuel-efficient automobile can be provided. However, when applied to a brake piston of an automobile, 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]
The basic configuration of the sliding member 10 is the same as that of the first embodiment, as shown in FIG.

The substrate 2 is composed of an aluminum alloy 101 and an oxide film 3 covering the surface thereof. The aluminum alloy 101 is made of an A6061-T6 material of an Al—Mg—Si alloy. The coating 1 is formed on the surface of the base material 2 covered with the oxide film 3 by using the UBMS method. The coating 1 is formed of a conductive layer 4, a buffer layer 5, an inclined layer 6, and a diamond-like carbon layer 7 from the substrate 2 side toward the outside. The surface roughness Ra of the coating 1 is finished to be 0.15 μm.

Specifically, the film 1 was formed under the conditions shown in FIG. 3C. The horizontal axis represents the film formation time, and the vertical axis represents the target input power and bias voltage.

Thereafter, until 44 minutes have elapsed from the start of film formation, 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 of 150V. Also in this step, the chromium target input power is 1.5 kW, and the carbon target input power is 0 kW.

Finally, an inert gas and a hydrocarbon gas are introduced until 130 minutes have elapsed from the start of film formation, and the diamond-like carbon layer 7 is formed while applying a bias voltage of 50V. In this step, the chrome target input power is 0 kW and the carbon target input power is 3.0 kW.

By using the UBMS method, the conductive layer 4 can be formed on the surface of the base material 2 having electrical insulation for the oxide film 3, so that the buffer layer 5, the gradient layer 6 and the diamond-like carbon layer 7 can be formed. It becomes possible.

In this comparative example, the film 1 had a thickness of 1.8 μm, a surface roughness Ra of 0.24 μm, and a hardness of 9 GPa. And the friction coefficient computed by the friction test was 0.24. Although wear was observed on the surface of the ball 13, the amount of wear was slight. On the other hand, wear was observed on the surface of the coating 1 after the friction test.

As described above, the sliding member of this comparative example is excellent in corrosion resistance and hardly wears the rubber of the mating member 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 aluminum alloy 101 is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a fuel-efficient automobile can be provided. However, when applied to a brake piston of an automobile, the coating 1 on the surface of 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 during braking is reduced, the piston does not return to the initial position when braking is released, and the disc rotor 22 and the brake pad 24 are dragged, thereby providing a reliable brake. Can not.

[Comparative Example 3]
Unlike the above-described Examples 1 to 3 and Comparative Examples 1 and 2, the surface of the aluminum alloy 101 formed of an Al—Mg—Si based alloy A6061-T6 material is covered with the oxide film 3. Coating 1 was not formed on the surface. The surface roughness Ra of the substrate 2 is finished to 0.02 μm.

For this reason, there is no coating for blocking pinholes in the oxide film 3 on the surface of the substrate 2, and the corrosion resistance is low.

In this comparative example, the friction coefficient was as low as 0.13. As for the value of the friction coefficient, the sliding amount between the sliding member and the ball 13 becomes excessive. In addition, abrasion scratches were observed on the surface of the substrate 2 after the friction test. Although wear was observed on the surface of the ball 13, 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 ball 13.

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 reduce the friction coefficient. When the sliding member of this comparative example is applied to an automobile, since the aluminum alloy 101 is used for the base material 2, the entire automobile can be reduced in weight, and as a result, a fuel-efficient automobile can be provided. However, when applied to a brake piston of an automobile, the brake piston wears, and further, the amount of rollback at the time of braking decreases, and the piston does not return to the initial position when the brake is released. Causes dragging. For this reason, a reliable brake cannot be provided.

1 hard carbon coating, 2 base material, 3 oxide film, 4 conductive layer, 5 buffer layer, 6 inclined layer, 7 diamond-like carbon layer, 10 sliding member, 11 test piece, 12 worktable, 13 balls, 14 shafts, 15, 16 Weight, 17 Vise, 18 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

A sliding member in which a conductive layer, a buffer layer, and a diamond-like carbon layer are sequentially laminated on a surface of a base material, wherein the base material includes an aluminum alloy and an aluminum oxide layer covering the aluminum alloy, and the buffer layer Is a layer that improves adhesion to the base material and supplements the hardness of the base material, and the surface roughness Ra of the diamond-like carbon layer calculated according to JIS B 0601 is 0.15 to A sliding member characterized by being 0.5 μm.
The sliding member according to claim 1, wherein the conductive layer contains at least one selected from the group consisting of aluminum, chromium, and titanium.
The sliding member according to claim 1 or 2, wherein the buffer layer contains at least one selected from the group consisting of chromium nitride and titanium nitride.
The sliding member according to any one of claims 1 to 3, wherein the buffer layer includes at least one selected from the group consisting of 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 graded layer is a mixture of carbon and metal or a metal carbide, and the content of the metal contained in the graded layer decreases from the base side toward the outside, and the graded layer contains the metal. 6. The slide according to claim 5, wherein the carbon content increases from the base material side toward the outside, and the metal is at least one selected from the group consisting of aluminum, chromium, and titanium. A moving member.
The sliding member according to any one of claims 1 to 6, wherein the diamond-like carbon layer has a surface hardness of 10 to 30 GPa.
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, wherein the sliding member according to any one of claims 1 to 8 is used.
Forming a conductive layer by sputtering or ion plating on a surface of the aluminum alloy covered with an aluminum oxide layer, and applying a bias voltage to the surface of the conductive layer; Improving the adhesion to the base material and forming a buffer layer for compensating the hardness of the base material, forming a gradient layer on the surface of the buffer layer, and on the surface of the gradient layer Forming a diamond-like carbon layer having a surface roughness Ra calculated in accordance with JIS B 0601 of 0.15 to 0.5 μm.