JP2009035584A - Sliding member - Google Patents

Abstract

To provide a sliding member having a DLC layer having excellent adhesion to a substrate.
A sliding member of the present invention has a base material, at least one element selected from silicon, tungsten, chromium and titanium, and carbon, and proceeds in the thickness direction from the surface to the base material direction. As a result, it has a gradient layer formed on the surface of the base material in a state where the carbon content is reduced, and a diamond-like carbon layer formed on the surface of the gradient layer.
[Selection figure] None

Description

  The present invention relates to a sliding member in which a diamond-like carbon layer forms a sliding surface.

  The sliding member is required to have high wear resistance and low friction coefficient and counterpart material attack. In order to satisfy such requirements, the sliding surface has been formed of diamond-like carbon (hereinafter referred to as DLC). That is, the DLC film is formed on the surface of the base material. The DLC film is a hard film having amorphous carbon.

  The DLC film is formed by using a PVD method such as a vacuum deposition method, a sputtering method or an ion plating method, a CVD method such as a thermal CVD method, a high frequency plasma CVD method, a microwave plasma CVD method or a direct current plasma CVD method. A hard film is formed on the surface. Among these film forming methods, the direct current plasma CVD method is used because the management of the film forming conditions is easy.

  However, the DLC film formed by the direct current plasma CVD method has a problem of low adhesion to the surface of a base material (particularly, a base material made of an iron-based metal such as steel). Conventionally, in order to improve the adhesion between the base material and the DLC film, the surface of the base material is subjected to surface treatment, and the DLC film is formed on the surface. As the surface treatment applied to the substrate, for example, nitriding treatment has been used. However, the nitriding treatment has a problem that the treatment temperature is high, and the characteristics of the substrate change depending on the treatment temperature. Specifically, when the base material is made of steel, it is treated at about 500 ° C. during nitriding, and so-called annealing occurs due to exposure to this treatment temperature. Further, when the base material is made of stainless steel, Cr contained in the stainless steel is nitrided (sensitized).

  Moreover, as a method for improving the adhesion between the substrate and the DLC film, for example, Patent Documents 1 and 2 disclose a method of forming an intermediate layer and a mixed layer on the surface of the substrate.

  In Patent Document 1, in a DLC thin film including a DLC layer formed on a base material via an intermediate layer, a mixed component layer composed of a component of the intermediate layer and carbon is interposed between the intermediate layer and the DLC layer. Further, it is disclosed that the composition of the mixed component layer is changed stepwise or continuously in the components of carbon and the intermediate layer.

In Patent Document 2, a base material made of high-speed tool steel or cemented carbide is coated with a hard material containing TiN, TiCN, TiAlN, A ₂ O ₃ or a combination thereof, and an intermediate layer of silicon alone is formed. A tool member is disclosed in which a mixed layer made of a component containing silicon and carbon or silicon, carbon and nitrogen is formed on the intermediate layer, and a hard film containing DLC is coated on the mixed layer.

In the methods disclosed in Patent Documents 1 and 2, it is necessary to form an intermediate layer on the surface of the substrate, and the number of steps for forming a DLC layer having high adhesion has been increased. That is, a large cost is required for forming the DLC layer.
JP 2000-256850 A JP 2000-176705 A

  This invention is made | formed in view of the said actual condition, and makes it a subject to provide the sliding member which has a DLC layer excellent in adhesiveness with a base material.

  In order to solve the above-mentioned problems, the present inventors have studied the sliding member having a surface made of DLC, and as a result, have come to make the present invention.

  The sliding member of the present invention has a base material, at least one element selected from silicon, tungsten, chromium and titanium, and carbon, and contains carbon in the thickness direction from the surface toward the base material direction. It is characterized by having a gradient layer formed on the surface of the base material in a reduced ratio and a diamond-like carbon layer formed on the surface of the gradient layer.

  In the sliding member of the present invention, an inclined layer having excellent adhesion to the DLC layer is formed between the base material and the DLC layer. For this reason, the sliding member of this invention became a sliding member with which the DLC layer contact | adhered with high adhesive force.

  The sliding member of this invention has a base material, the inclination layer formed in the surface of a base material, and the DLC layer formed in the surface of an inclination layer.

  A base material is a member in which a sliding surface is formed with the sliding member of this invention. In the present invention, the material and shape of the substrate are not particularly limited. Examples thereof include resins such as polyethyl ether ketone (PEEK), polyimide (PI), and polyamideimide (PAI), and metals mainly composed of iron, aluminum, steel, super steel, and the like. Of these materials, iron-based metals are more preferable.

  The gradient layer has at least one element selected from silicon, tungsten, chromium and titanium, and carbon, and the base material in a state where the content ratio of carbon decreases from the surface toward the base material in the thickness direction. It is a layer formed on the surface of Since the inclined layer has at least one element selected from silicon, tungsten, chromium, and titanium, and carbon, both the base material and the DLC layer can be firmly adhered to each other.

  The gradient layer is a layer in which at least one element and carbon are present in an amorphous state. Further, at least one element and part of the carbon element may form a compound.

  At least one element selected from silicon, tungsten, chromium, and titanium, which are elements constituting the gradient layer, is an element that can firmly adhere the gradient layer and the substrate. On the substrate surface side of the gradient layer, at least one element is present more than carbon, and adhesion between the gradient layer and the substrate is ensured. In the vicinity of the interface with the substrate, it is preferable that the abundance ratio of the at least one element is high, and it is more preferable that the at least one element is substantially composed of this at least one element. In particular, it is preferable to use silicon as at least one element from the viewpoint of bondability with an iron-based metal often used for the base material of the sliding member.

  And in the gradient layer, the content ratio of carbon gradually decreases from the surface toward the base material. That is, more carbon atoms exist than at least one element on the surface side of the gradient layer. Carbon atoms can firmly adhere to the DLC layer formed on the surface of the gradient layer. It is preferable that the existence ratio of carbon atoms is as high as possible on the surface of the gradient layer.

  There is no particular limitation on the rate of increase of the carbon atom existing ratio (carbon concentration change gradient) in the inclined layer. Further, the thickness of the inclined layer is not particularly limited because it varies depending on the carbon atom existing ratio.

  The DLC layer is a layer made of DLC formed on the surface of the gradient layer. The surface of this DLC layer becomes the sliding surface of the sliding member of the present invention. DLC constituting the DLC layer is a substance containing carbon or hydrocarbon in an amorphous state. The DLC is a conventionally known DLC, more preferably a DLC containing silicon.

  Here, when DLC is DLC containing silicon, the content ratio of silicon, carbon, hydrogen and the like is not particularly limited, and is a ratio capable of forming a sliding surface when used as a sliding member. I just need it.

  DLC can be set in the range of 1% by weight to 80% by weight of silicon when the total amount of DLC is 100% by weight, but a more preferable range is 5% by weight to 50% by weight, and is most preferable. The range is from 10% to 40% by weight. When the proportion of silicon is less than 1% by weight, a good DLC layer cannot be formed. On the other hand, when the silicon content is less than 10% by weight, wrinkles are likely to occur during film formation by DC plasma CVD, and the DLC layer itself becomes brittle. On the other hand, when the proportion of silicon exceeds 80% by weight, the proportion of carbon decreases, and the attack of the counterpart material when sliding as a sliding member increases.

  The thickness of the DLC layer is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. When the thickness of the DLC layer is less than 0.5 μm, the durability life against wear is shortened and it is not suitable for practical use as a sliding member. If the thickness exceeds 10 μm, the DLC layer itself becomes brittle.

  The manufacturing method of the DLC layer is not limited, but is preferably formed by a direct current plasma CVD method. The direct current plasma CVD method is a method of forming a DLC layer on a substrate surface by discharging a direct current in a DLC layer forming gas atmosphere mainly composed of a carbon compound gas. The direct current plasma CVD method is a method capable of forming a DLC layer at a relatively low temperature without exposing the substrate to a high temperature, and in particular, a method capable of forming a DLC layer at a low temperature of 300 ° C. or lower. is there. That is, by using a direct current plasma CVD method for forming the DLC layer, the DLC layer can be formed without altering the base material.

  In the sliding member of the present invention, the method for forming the inclined layer is not particularly limited, but it is preferably produced by the direct current plasma CVD method in the same manner as the DLC layer. When the direct current plasma CVD method is used, the gradient layer and the DLC layer can be formed by adjusting the gas atmosphere in the reaction chamber in which plasma is generated. And both layers can be formed continuously by forming a graded layer and a DLC layer by direct-current plasma CVD method. As a result, the interface between the gradient layer and the DLC layer does not exist, and both layers are bonded more strongly. Furthermore, since both layers can be formed in one step, an increase in cost required for manufacturing can be suppressed.

  In the sliding member of the present invention, the DLC layer is firmly adhered to the substrate through the inclined layer, and the DLC layer is hardly peeled off during sliding. For this reason, the sliding member of this invention can be used for sliding members of apparatuses, such as machine parts, such as a bearing, a motor vehicle parts, such as a pump and a shaft, a tool holder, and a precision slide.

  The sliding member of this invention can be manufactured with the following manufacturing methods, for example.

First, a material to be processed, which is a base material, is disposed on a table in a vacuum vessel that partitions a reaction chamber, and a vacuum is drawn to remove gas remaining in the vacuum vessel. Here, for example, the exhaust is performed to 1 × 10 ⁻⁴ Torr or less.

Next, a gas for raising temperature such as hydrogen (H ₂ ) gas is introduced while continuously exhausting, and discharge is started by direct current discharge or high frequency discharge, and the material to be treated is heated to a predetermined temperature by plasma energy. In order to prevent deterioration of the base material, it is preferable to raise the temperature so as not to exceed 300 ° C.

Next, a silicon compound gas is introduced into the vacuum vessel, and the inside of the vacuum vessel is set to a silicon compound gas atmosphere. It discharges in this gas atmosphere, and forms the film which has silicon as a main component on the base-material surface. Here, the silicon compound gas atmosphere is composed of an atmosphere gas and a silicon compound gas. As the silicon compound gas, tetrachlorosilane (SiCl ₄ ), tetrafluorosilane (SiF ₄ ), trichlorosilane (SiHCl ₃ ), tetramethylsilane (TMS; Si (CH ₃ ) ₄ ), or the like can be used. The silicon compound gas may further contain hydrogen gas. As the atmospheric gas, a commonly used gas such as hydrogen (H ₂ ) or argon (Ar) can be used.

Then, when a coating containing silicon as a main component is formed or when a predetermined time has elapsed, a predetermined amount of carbon compound gas is further introduced into the vacuum vessel. As the carbon compound gas, methane (CH ₄ ), ethylene, acetylene, benzene, other hydrocarbon gas (C _m H _n ), or the like can be used.

  Thereafter, the amount of carbon compound gas introduced is gradually increased. At this time, the amount of silicon compound gas introduced may be reduced. The carbon compound gas concentration contained in the gas constituting the atmosphere in the vacuum vessel gradually increases.

  By introducing the carbon compound gas, the concentration of the carbon compound gas contained in the gas constituting the atmosphere in the vacuum vessel gradually increases. For this reason, the coating film formed on the surface of the base material has a higher carbon content as it proceeds in the surface direction.

  Then, the introduction amount of the carbon compound gas is increased, and finally, the introduction amount of the carbon compound gas and the silicon compound gas is set to an amount capable of forming DLC to form a coating film. The composition of the special thin film forming gas is appropriately determined depending on the raw material gas, the processing temperature, and the like, and the entire flow rate is determined by the balance between the volume of the vacuum vessel and the exhaust amount.

  In this way, the sliding member of the present invention having a high hardness and an extremely low friction coefficient can be easily formed.

  Hereinafter, the present invention will be described using examples.

  As an example, a sliding member having an inclined layer and a DLC layer was manufactured.

Example 1
A gradient layer and a DLC layer were formed on the surface of a base material made of an iron-based metal by a DC plasma CVD method. A plasma CVD processing apparatus 1 used in this process is shown in FIG.

  First, on a base 12 provided in the center of the plasma reaction chamber 11 made of stainless steel, a square tile-shaped substrate 13 having a size of 30 × 30 mm and a thickness of 5 mm is placed at a distance of 350 mm from the center of the base 12. Two were arranged. A cooling water pipe (not shown) for sending cooling water is attached to the inside of the support column 14 of the base 12.

Next, after the plasma reaction chamber 11 is sealed, the residual gas becomes 1 × 10 ⁻⁴ Torr by a rotary pump (not shown) of a vacuum pump and a diffusion pump (not shown) connected to the gas outlet pipe 15. The pressure was reduced to. The gas introduction pipe 16 is connected to various gas cylinders (both not shown) via a control valve.

Next, hydrogen gas is introduced as a temperature raising gas into the furnace depressurized to 133 × 10 ⁻⁴ Pa (1 × 10 ⁻⁴ Torr), and the pressure in the reaction chamber 11 is set to 133 Pa (1 Torr) while evacuating simultaneously. Adjusted to keep. Then, a DC voltage of several hundred volts is applied between the stainless steel anode plate 17 and the cathode (base) 12 provided inside the reaction chamber 11 to start discharging, and ions are applied until the substrate surface reaches 300 ° C. The temperature was raised by impact. Here, the direct current circuit is composed of an anode 17 and a cathode 12, and the power is controlled by an input from a two-color thermometer (not shown) that measures the temperature of the internal substrate, so that the temperature of the substrate is kept constant. Work to keep.

Next, tetramethylsilane (TMS; Si (CH ₄ ) ₄ ) gas, hydrogen (H ₂ ) gas, and argon (Ar) gas are introduced into the reaction chamber 11 at flow rates of 6, 60, and 60 sccm, respectively. Then, a chemical vapor deposition treatment was performed by maintaining a silicon compound gas atmosphere with a total pressure of 533 Pa and maintaining the substrate temperature at 300 ° C. for 10 minutes while maintaining DC discharge.

After 10 minutes, methane (CH ₄ ) gas was further introduced into the reaction chamber 11 at 50 sccm to form a mixed gas atmosphere of silicon compound gas and carbon compound gas at a total pressure of 533 Pa, while maintaining the temperature of the substrate at 300 ° C. The chemical vapor deposition process was performed by maintaining the DC discharge for 10 minutes.

Thereafter, the chemical vapor deposition treatment was performed by setting the flow rate of methane (CH ₄ ) gas introduced into the reaction chamber 11 to 100 sccm and maintaining the DC discharge for 20 minutes.

  After completion of the treatment for 20 minutes, the discharge was stopped, the substrate was cooled under reduced pressure (533 Pa), and the substrate was taken out from the reaction chamber 11. Thereby, the inclined layer and the DLC layer were formed on the surface of the substrate.

  In the manufactured sliding member of this example, the inclined layer is formed on the surface of the base material, and the DLC layer is formed on the surface of the inclined layer. The gradient layer has hydrogen, carbon, and silicon, and the carbon content decreases (the silicon content increases) as the thickness direction proceeds from the surface to the base material. The DLC layer is made of DLC. And in the sliding member of a present Example, the clear interface of a DLC layer and an inclination layer was not able to be confirmed.

  In the manufacture of the inclined layer of the sliding member of this example, the amount of methane gas introduced into the reaction chamber 11 was introduced at a flow rate of 0 sccm, 50 sccm, and 100 sccm. Thus, although the amount of methane gas introduced into the reaction chamber 11 was introduced in two stages of inflow, the carbon content in the inclined layer of the sliding member changed smoothly. This is because the ratio of methane gas to the atmosphere in the reaction chamber 11 gradually increased as the introduction of methane gas was started.

(Comparative example)
A nitride layer was formed on the surface of a base material made of iron-based metal, and a DLC layer was formed on the surface by direct current plasma CVD.

  First, a base material made of an iron-based metal similar to that in Example 1 was prepared, and held at 300 ° C. in a nitrogen gas atmosphere to form a nitride film.

  Subsequently, the plasma CVD processing apparatus 1 used in Example 1 was used to perform the same process as when the DLC layer was formed in Example 1.

  Thereby, the sliding member of this comparative example was formed.

  In the sliding member of this comparative example, a nitride film layer is formed on the surface of a base material made of an iron-based metal, and a DLC layer is formed on the surface of the nitride film layer.

(Evaluation)
In the sliding members of Example 1 and Comparative Example, the adhesion of the inclined layer and the DLC layer (surface coating) was evaluated.

  Evaluation of the adhesion of the surface coating was performed by conducting the following tests on the sliding members of Example 1 and the comparative example, and confirming the state of the surface coating (DLC layer) after the test. Moreover, the sliding member was produced by using two types of materials of the base material of the sliding member, SCM415 and SUS440C, and each was tested. The evaluation results are shown in Table 1.

  A steel ball was hit under the Rockwell hardness (HRC) measurement conditions to give an impression on the surface of the sliding member, and the surface coating and the state of the impression were confirmed and evaluated. Specifically, using the tester shown in FIG. 2, a 1/16 steel ball was hit using the pressure of air. The evaluation of the crack was ○ when no crack was confirmed on the surface coating, and × when the crack was confirmed. Moreover, peeling of the surface film could not be confirmed in any of Examples and Comparative Examples (all were evaluated as “good”).

  As shown in Table 1, cracks and indentation interface peeling were not observed on the surface films of the sliding members of Example 1 and Comparative Example. In particular, when the substrate was SUS440C, cracks were confirmed in the DLC layer in the comparative example, but no cracks were confirmed in Example 1. Thus, it can be seen that the sliding member of Example 1 has a high adhesion strength equal to or higher than that of the conventional sliding member (comparative example).

  In addition, the tribological characteristics of the sliding members of Example 1 and the comparative example and having the base material made of SCM415 were measured. The tribological characteristics were measured by the method shown below, and the measurement results are shown in FIG.

  Using a reciprocating Ball-on-Disk tester, a sliding test was performed for 1 hour under conditions of mating material: bearing steel (SUJ-2), load: 10 N, speed: 2 Hz, stroke: 10 mm, and no lubrication. Made and evaluated.

  As shown in FIG. 3, the sliding member of Example 1 and the comparative example did not show a great difference in the change in the friction coefficient of the sliding surface. That is, it was confirmed that the sliding member of Example 1 exhibited the same sliding characteristics as the conventional sliding member even when sliding was repeated.

  Further, FIG. 4 shows changes in mechanical properties accompanying tempering of carbon steel. As shown in FIG. 4, the higher the tempering temperature of the carbon steel, the lower the hardness after treatment (HRC). The sliding member (base material: SCM415) of Example 1 and the comparative example is not exposed to a temperature exceeding 300 ° C. in the surface coating forming process. For this reason, the significant fall of the hardness based on formation of a surface film is suppressed.

  Furthermore, since it is not exposed to nitrogen gas at a high temperature when forming a surface coating on the surface of the base material, the base material of the sliding member of Example 1 and Comparative Example is included in the base material in the case of SUS440C. Cr does not form nitrides. That is, a significant decrease in hardness due to the formation of the surface coating is suppressed.

  As described above, in the sliding member of Example 1, the inclined layer causes the DLC layer to adhere to the substrate with high adhesion. Further, the sliding member of Example 1 exhibits excellent sliding characteristics on the sliding surface made of the DLC layer. Furthermore, in the sliding member of Example 1, the heating temperature at the time of forming the inclined layer and the DLC layer was 300 ° C. at the maximum, and the characteristics of the base material made of an iron-based metal were not deteriorated. In addition, the sliding member of Example 1 was able to keep the heating temperature at the time of forming the inclined layer and the DLC layer low, and the cost required for manufacturing could be reduced.

(Example 2)
A gradient layer and a DLC layer were formed on the surface of a base material made of an iron-based metal by a DC plasma CVD method. The plasma CVD processing apparatus used in this process is the same apparatus as that used in Example 1.

A base material is placed in the plasma reaction chamber, hydrogen gas is introduced as a temperature-raising gas into a furnace depressurized to 133 × 10 ⁻⁴ Pa (1 × 10 ⁻⁴ Torr), and the pressure in the reaction chamber is simultaneously reduced while evacuating. Was adjusted to be 133 Pa (1 Torr). Then, a DC voltage of several hundred volts was applied between the stainless steel anode plate and the cathode (base) to start discharging, and the temperature was increased by ion bombardment until the surface of the base material reached 300 ° C.

Next, tetramethylsilane (TMS; Si (CH ₄ ) ₄ ) gas, methane (CH ₄ ) gas, hydrogen (H ₂ ) gas, and argon (Ar) gas are supplied into the reaction chamber at flow rates of 6, 0, Chemical vapor deposition is performed by introducing a 0 and 0 sccm gas atmosphere of a silicon compound gas and a carbon compound gas with a total pressure of 533 Pa and maintaining a substrate temperature at 300 ° C. and maintaining a DC discharge for 10 minutes. It was.

After 10 minutes, the introduction amount of methane (CH ₄ ) gas was further introduced into the reaction chamber at 50 sccm to obtain a mixed gas atmosphere of silicon compound gas and carbon compound gas at a total pressure of 533 Pa, and the temperature of the material to be treated was set to 300 ° C. The chemical vapor deposition treatment was performed by maintaining the DC discharge for 10 minutes while maintaining.

Thereafter, the chemical vapor deposition treatment was performed by setting the flow rate of methane (CH ₄ ) gas introduced into the reaction chamber to 100 sccm and maintaining DC discharge for 20 minutes.

  After the treatment for 20 minutes, the discharge was stopped, the substrate was cooled under reduced pressure (533 Pa), and the substrate was taken out from the reaction chamber. Thereby, the inclination layer and the DLC layer were formed in the surface of a base material.

  As with the sliding member of Example 1, the configuration of the sliding member was confirmed, and it was confirmed that an inclined layer was formed on the surface of the base material and a DLC layer was formed on the surface of the inclined layer. The gradient layer has hydrogen, carbon, and silicon, and the carbon content decreases (the silicon content increases) as the thickness direction proceeds from the surface to the base material. And it has confirmed that it contained 50-80 at% of carbon in the interface vicinity with the base material of an inclination layer. The DLC layer is made of DLC. And in the sliding member of a present Example, the clear interface of a DLC layer and an inclination layer was not able to be confirmed.

  The sliding member of Example 2 has the same configuration as that of the sliding member of Example 1 except that the content ratio of each element in the inclined layer is different, and exhibits the same effect as that of Example 1.

It is the schematic of the plasma CVD processing apparatus used in the Example. It is the schematic of the testing apparatus used when evaluating the adhesiveness of the surface film of a sliding member. It is the figure which showed the result of the tribological characteristic of the sliding member of Example 1 and a comparative example. It is the figure which showed the relationship between the mechanical property of carbon steel, and tempering temperature.

Explanation of symbols

1: Plasma CVD processing apparatus 11: Plasma reaction chamber 12: Base 13: Base material 14: Support column 15: Gas outlet pipe 16: Gas inlet pipe

Claims (4)

A substrate;
The surface of the base material in a state in which at least one element selected from silicon, tungsten, chromium and titanium and carbon are included, and the carbon content decreases in the thickness direction from the surface toward the base material direction. An inclined layer formed on
A diamond-like carbon layer formed on the surface of the inclined layer;
A sliding member characterized by comprising:   The sliding member according to claim 1, wherein the base material is made of an iron-based metal.   The sliding member according to claim 1, wherein the diamond-like carbon layer is formed by a direct current plasma CVD method.   The sliding member according to claim 1, wherein the inclined layer has silicon and carbon.

Images