WO2014196259A1

WO2014196259A1 - Sliding component

Info

Publication number: WO2014196259A1
Application number: PCT/JP2014/059920
Authority: WO
Inventors: 一等杉本; 拓小野寺
Original assignee: 株式会社日立製作所
Priority date: 2013-06-06
Filing date: 2014-04-04
Publication date: 2014-12-11
Also published as: JPWO2014196259A1

Abstract

A sliding component which is provided with: a component that is provided with a hard carbon coating film; and a steel component that is in sliding contact with the component. The hard carbon coating film comprises at least a first layer that forms the surface layer and a second layer that is below the first layer. The first layer contains C, H and at least one of elements X (B, Cr, Ti), and the second layer contains at least one of the elements X which are contained in the first layer. The concentration of the elements X in the first layer is lower than that in the second layer.

Description

Sliding parts

The present invention relates to a sliding part.

Low friction sliding parts have been developed for the purpose of reducing fuel consumption of internal combustion engines and extending the life of parts. In recent years, development of solid lubricating films has been particularly active, and hard carbon films have been developed. The hard carbon film is a carbon film called DLC (diamond-like carbon), amorphous carbon, amorphous carbon or the like. Hard carbon film includes both sp ² bonds and sp ³ bonds to the binding between the carbon atoms, no definite crystal structure (without grain boundaries) an amorphous structure, the sp ³ bonds The friction coefficient is low due to the high hardness and toughness derived from it and the self-lubricating property derived from sp ² bonding. There are PVD methods such as sputtering and arc ion plating, plasma CVD, etc. as film forming methods, and it is general to produce a hydrogen-containing carbon film using a part of hydrocarbon gas as a raw material.

For example, Patent Document 1 and Patent Document 2 have been reported as hard coatings utilizing the self-lubricating property of carbon or sliding parts using the same. Patent Document 1 discloses a hard film in which a graphite particle deposition layer defined by Raman spectroscopic analysis is formed on the surface of a DLC layer. The graphite particle deposition layer is said to have rapid self-lubricating property in the early stage of sliding, that is, conformability, and can contribute to lowering the friction coefficient in the initial stage of use of the sliding part. Patent Document 2 relates to a similar conforming layer, and discloses a sliding member using DLC containing N, H, and Si formed by DC pulse plasma CVD as the conforming layer.

JP 2007-162099 A JP 2011-1598

However, in the above-mentioned patent document, there is room for improvement in that the familiar layer is worn away by repeated use.

An object of the present invention is to obtain a sliding component having low friction characteristics that is stable over a long period of time.

In order to achieve the above object, the present invention provides a sliding component comprising a component provided with a hard carbon coating and a steel component slidably contacted with the hard carbon coating, wherein the hard carbon coating comprises a first layer on the surface layer and a first layer below the first layer. Two layers, wherein the first layer includes at least one element X (B, Cr, Ti) and C and H, and the second layer includes the element X contained in the first layer. At least one of them is included, and the first layer has a lower element concentration of the element X than the second layer.

According to the present invention, it is possible to obtain a sliding component having low friction characteristics that is stable over a long period of time.

It is a schematic diagram of a sliding component. It is the figure which simulated the chemical adsorption reaction in the sliding surface of the sliding apparatus in sliding. It is the cross-sectional schematic diagram which showed an example of the plunger pump and its peripheral structure. It is the cross-sectional schematic diagram which showed an example of the cam, the valve lifter, and its peripheral structure. It is a cross-sectional schematic diagram of a repeated friction test.

As shown in FIG. 1, the sliding component of the present invention includes at least a component 3 having a hard carbon film 1 on the surface of a base material 2 and a steel component 4. The hard carbon film of the part before use has a layer structure of two or more layers having at least a first layer (surface layer) 11 and a second layer 12. The first layer contains at least one element X (B, Cr, Ti) and carbon and hydrogen. The second layer includes at least one element X included in the first layer, and the first layer has a lower element concentration of the element X than the second layer. For example, when the first layer includes B and Cr, the second layer may include Ti that is not included in the first layer, but includes at least one of B and Cr.

As shown in FIG. 2, during the sliding of the hard carbon film and the steel part 4, a part of the carbon body is discharged from the first layer of the hard carbon film and adsorbs to the steel part surface away from the film surface. The carbon body discharged from the first layer can be easily adsorbed on the surface of steel parts as compared with pure carbon, and can have a strong transfer reaction. Specifically, amorphous carbon mainly composed of a carbon network of sp ² bonds easily retains sp ³ bonds such as —CH ₃ by including H, but by including the element X in this bond, It becomes easy to combine with O that is bound to Fe element on the surface of the steel part, and as a result, the discharged carbon body is firmly adsorbed on the surface of the steel part.

Here, in contrast to the first layer that retains the inherent self-lubricating characteristics of C, the second layer preferably has a microstructure that suppresses self-lubricating characteristics and prevents wear due to frictional heat. B is capable of forming a heat-resistant BC bond, and Cr or Ti is an element capable of forming a heat-resistant carbide. Both elements combine with C to achieve high hardness characteristics and high heat resistance characteristics. It is an element that can achieve both. If the concentration of element X in the second layer is the same as or lower than that of the first layer, the second layer exhibits the same self-lubricating characteristics as the first layer due to an increase in the proportion of C, and is rubbed by friction. As a result, the entire hard carbon film is significantly worn out.

Therefore, the first layer contains a large amount of C to actively self-lubricate, and a small amount of element X helps self-lubricating characteristics. On the other hand, the second layer provided immediately below the first layer has a higher element X concentration than the first layer in order to protect the hard carbon film itself from wear including self-lubrication.

In the figure, the layers are clearly separated from each other, but the elements contained in the layers slightly diffuse to the adjacent layers. Therefore, there is a gentle concentration gradient in the film thickness direction at the boundary between layers. In the present invention, a portion where the concentration is inclined is allowed as an interlayer (boundary).

As a preferred embodiment of the sliding part, when the element X is Cr and the sum of Cr and C in one layer is 100%, the Cr concentration of the first layer is 0.05 atomic% or more and 0.12 atomic%. Hereinafter, the Cr concentration of the second layer is set to a range of 0.24 atomic% or less. When the Cr concentration of the first layer is 0.05 atomic% or more with respect to the concentration range, transfer to the steel part is promoted and a stable friction coefficient is easily obtained. When the Cr concentration in the first layer is 0.12 atomic% or less, the initial friction coefficient can be sufficiently lowered. When the Cr concentration of the second layer is 0.24 atomic% or less, the film hardness is high and wear is difficult.

The sliding component preferably has a first layer hardness of 15 GPa or less and a second layer of 24 GPa or more when measured by an instrumented indentation hardness test. The kind of element X at this time does not matter. The instrumented indentation hardness test specified in ISO14577-1 is a device that can analyze the hardness of a hard carbon film microscopically. In the case of a hard carbon film containing hydrogen, the lower the hardness, the higher the self-lubricating property and the tendency to wear away.By making the first layer, which requires conformability, 15 GPa or less, it can contribute to lower friction. Contributing to wear prevention by making the two layers 24GPa or more.

As a preferred embodiment of the sliding part, the element X is B, and N is contained in the same degree as B. When B and N are added in amorphous carbon, BN bonds with high hardness and high heat resistance can be formed, so wear is reduced more especially when both B and N are included in the second layer. Can be formed.

As a preferred embodiment of the sliding component, it is preferable to have a film structure in which an intermediate layer that enhances adhesion is provided between the second layer and the substrate. When the base material is a steel material, it is preferable to use an appropriate combination of metal layers such as Cr, Ti, Si, and W and these metal carbide layers as an intermediate layer for improving adhesion.

The film structures such as the first layer, the second layer, and the intermediate layer can be used in appropriate combination.

¡In addition to C, H, elements X and N, Ar and O may be mixed in the sliding parts as inevitable elements in production. Even in this case, it is preferable to control O at 12 atomic% or less and Ar at 18 atomic% or less. If the content exceeds the specified range, the film becomes brittle, which is not preferable.

It is preferable that the sliding parts are arranged on various automobile parts, since the surface can take advantage of the characteristics of promoting self-lubrication while maintaining the hardness of the coating itself. Examples of components disposed in the internal combustion engine include a valve lifter, a tappet, an adjusting shim, a cam, a camshaft, a rocker arm, a piston, a piston pin, a piston ring, a timing gear, and a timing chain. In addition, examples of the sliding parts arranged in the fuel supply pump and the fuel injection system include an injector, a plunger, a cylinder, a cam, and a vane. However, the present invention is not limited to these, and can be widely applied to other sliding parts.

As shown in FIG. 3, in the case of a plunger-type fuel supply pump, the cylinder 503 and the plunger 501 slide. 502 is an oil seal, 504 is a lifter, 505 is a cam, 506 is a fuel flow path, 507 is a suction side valve, and 508 is a discharge side valve. By providing the hard carbon film on the surface of either the cylinder or the plunger, low friction characteristics can be obtained over a long period of time, and a high-performance product that does not cause seizure can be provided.

In the internal combustion engine shown in FIG. 4, the valve lifter 601 and the cam 602 slide. 603 is a valve, 604 is an intake duct or exhaust duct, and 605 is a combustion chamber.
By providing the hard carbon film on the surface of either the valve lifter or the cam, a low friction characteristic can be obtained over a long period of time, and an internal combustion engine with low fuel consumption can be provided.

The hard carbon film is preferably produced by a sputtering method using a solid carbon target and a hydrocarbon gas in combination, and it is preferable to use a film production apparatus incorporating a non-equilibrium magnetron sputtering technique with a relatively high plasma ionization rate. When conventional sputtering equipment is used, the energy of plasma is limited, and since plasma is mainly excited near the target, it is difficult to maintain a high excitation state near the substrate, which is the film forming material. It is. On the other hand, the non-equilibrium magnetron sputtering technique is a technique that can increase the plasma density on the substrate side by controlling the plasma distribution. When sputtering is carried out using an apparatus incorporating this technology, C and B, which are difficult to ionize, can take a higher-order excited state to form a non-equilibrium state, and by controlling the parameters, the hardness is 25 GPa or more. A hard film can be produced. Ar gas is usually used for plasma control. When controlling the composition ratio of the hard coating, a method of controlling by preparing two types of solid target containing element X and solid carbon target and adjusting the respective input power is preferable. Further, when N is contained, it is preferable to enclose a small amount of either or both of N gas and ammonia gas in the furnace.

(Preparation of hard carbon film of Example 1)
A steel substrate, a Cr target and a C target were set in a non-equilibrium magnetron sputtering device (UBMS ^TM manufactured by Kobe Steel). First, power is applied to the Cr target while flowing Ar gas, and a metal intermediate layer (thickness 0.1 μm) is deposited on the surface of the base material. Subsequently, additional power is applied to the C target and the metal carbide intermediate layer is applied. (Thickness 0.5 μm) was deposited. Thereafter, a small amount of methane gas was mixed in the Ar atmosphere in order to deposit amorphous hard carbon. Under the condition that the substrate application bias was increased, the Cr target power was decreased to increase the C target power, and a second layer containing Cr (thickness 1.7 μm) was deposited, and subsequently the applied bias was reduced, With the vacuum gas pressure increased, the input power of the Cr target was further reduced to deposit a first layer (thickness 0.5 μm) containing a small amount of Cr. According to the composition analysis measured with an XPS (X-ray photoelectron spectroscopy) analyzer, the atomic concentration ratio of Cr and C is “Cr: C = 5: 95” in the first layer and “Cr: C = 23: 77 ", confirming that the desired structure was obtained. When measured with an instrumented indentation hardness tester (Elionix ENT-110a), the hardness of the first layer was 9 GPa and the hardness of the second layer was 24 GPa.
(Production of hard carbon films of Examples 2 to 8 and Comparative Examples 1 to 8)
A hard carbon film having the composition shown in Examples 2 to 8 and Comparative Examples 1 to 8 was deposited on the substrate in the same procedure as in Example 1-1. A metal intermediate layer and a metal carbide intermediate layer were provided between the substrate and the hard carbon film. As a method for adding the element X, B was a boron carbide target, Cr was a Cr target, and Ti was a Ti target.
(Composition analysis)
When a film is produced with a sputtering apparatus, N, C, or O may be mixed into the film without intentionally entering the supply source. This mixed element is considered to have been obtained from residual air distributed in the furnace, water vapor and floating dust. When the purity of the supply gas such as Ar was set to 99.9% or more and the degree of vacuum and humidity in the furnace were changed and investigated, O inevitably mixed was less than 12 atomic%, and Ar was less than 18 atomic%. I understood that. In addition, the H concentration that cannot be analyzed by XPS was measured with an ERDA (elastic recoil detection method) analyzer, and the H concentration in the hard carbon films of the examples and comparative examples prepared with the sputtering device was 4 atom% to 25 atom%. It was found to be in the range.

(Repeated friction test)
Matsubara type friction and wear tester (manufactured by Orientec Co., Ltd., model: EFM-III) was used for the repeated friction test. The friction and wear test apparatus includes a plate test piece 701, a ring test piece 702, a heater 703, a torque measurement arm 704, a load cell 705, a test chamber 706, and heat retaining water 10. The plate test piece is obtained by using a steel material represented by SUS440B as a base material and forming a hard carbon film on the surface that slides with the ring test piece. As the ring test piece, a steel material represented by SKD10 was used. In the friction and wear test, the plate test piece was rotated so that the peripheral speed of the outer periphery of the sliding part was 0.5 m / s, and the ring test piece was slid with a maximum load of 10 kgf (maximum surface pressure of 8 MPa). . In order to accelerate the wear and tear of hard carbon, the test temperature was set higher than the normal temperature, and the hot water was always adjusted to 80 ° C. with a heater. The process of removing abrasion powder by blowing the friction surface with dry air after sliding for 0.5 hour was defined as one cycle, and this was repeated 20 cycles (total sliding time 10 hours). In addition, a precise jig was prepared so as to be contacted at the same position after the second cycle, and a test piece was set so as not to be displaced. The coefficient of friction up to the 20th cycle was confirmed, and the specimen after the test was observed.

As a result of repeated friction tests, it was confirmed that the sliding parts of Examples 1 to 8 can maintain low friction characteristics. In any test, it was confirmed that at least the second layer remained on the surface of the plate test piece. In addition, as a result of detailed analysis of the friction surface of the ring test piece with an EDX (energy dispersive X-ray spectroscopy) analyzer, it was confirmed that the carbon concentration was high in the friction part. It was confirmed that it was transferred.

Further, in Example 4, the Cr concentration of the first layer is relatively high as compared with the other examples. In this case, the coefficient of friction is slightly higher. Therefore, it is more preferable to control the Cr concentration of the first layer to 0.12 atomic% or less as in the other examples.

Further, in Example 5, the Cr concentration of the second layer is relatively high and the hardness is 18 GPa as compared with the other examples. In this case, slight wear was observed at the inner end of the friction part having a low peripheral speed. If the Cr concentration of the second layer is too high, the hardness of the hard carbon film cannot be maintained high, and thus wear easily occurs. Therefore, it is more preferable to control the Cr concentration of the second layer to 0.24 atomic% or less as in the other examples.

On the other hand, when the results of Comparative Examples 1 to 4 in which a hard carbon film having a single layer (the composition of the first layer and the second layer is the same in Table 1) are provided on the intermediate layer, Comparative Example 1 having a low Cr concentration are shown. In Comparative Example 2, the hard carbon layer was abraded and the intermediate layer was exposed, both of which resulted in a high coefficient of friction during the test. In particular, Comparative Example 1 with a low hardness exhibited significant wear. On the other hand, Comparative Example 4 with a high Cr concentration did not show significant wear, but the coefficient of friction was remarkably high from the start of the test. Comparative Example 3 having a Cr concentration between Comparative Example 2 and Comparative Example 4 showed a slight friction and a higher friction coefficient than the Example. From these results, it was found that a single layer hard carbon film containing Cr cannot achieve both a stable friction coefficient and wear resistance at any Cr concentration.

Comparative Example 5 does not contain an additive element in the first layer. This was low friction at the start of the test, but the coefficient of friction increased with each cycle, resulting in high friction. This shows that it is necessary to add a small amount of element X to the first layer. From the above, when Cr is used as the additive element, it is preferable to control the Cr concentration of the first layer to 0.05 atomic% or more and 0.12 atomic% or less, and the Cr concentration of the second layer to 0.24 atomic% or less.

Regarding the film hardness of the hard carbon film, it is preferable that the first layer that needs to have a low coefficient of friction be a low hardness, and the second layer that needs to have wear resistance be a high hardness. As a result of the friction test, the first layer is preferably 15 GPa or less in Example 3, and the second layer is preferably 24 GPa or more in Example 1.

Similarly, when B or Ti is added as an additive element other than Cr, it is confirmed that a stable low friction characteristic can be obtained by forming a hard carbon film with at least two layers with different additive element addition amounts. did. As a representative example, Example 6 and Example 7, Comparative Example 6 and Comparative Example 7 are shown.

In addition, when the additive element was B, it was confirmed that a hard carbon film with higher wear resistance can be formed by simultaneously adding N. In this case as well, a stable low friction characteristic can be obtained by using a two-layer structure with different addition amounts. As a representative example, Example 8 and Comparative Example 8 are shown. As a result of detailed analysis of the microstructure of the second layer of Example 8, carbon, B, and N are contained in an amorphous (non-crystal) structure, and particularly when the atomic concentrations of B and N are comparable. It has been found that it has a stable heat resistance and is difficult to wear. N is preferably contained in the second layer in order to improve the wear resistance, but it was confirmed that even if it is contained in the first layer, the friction coefficient is not greatly affected if it is contained in a small amount. If the first layer contains an amount of N equal to that of the second layer as in Comparative Example 8, the friction coefficient will be significantly increased.
(Plunger pump)
In the plunger pump which is one of the fuel supply pumps, a hard carbon film was coated on the plunger surface, and the actual machine was evaluated. As a result, it was confirmed that the sliding parts having the hard carbon film shown in Examples 1 to 8 showed excellent low friction and wear resistance characteristics.
(Valve lifter)
In a sliding environment of a valve lifter / cam of an internal combustion engine, a hard carbon film was coated on the surface of the valve lifter, and the actual machine was evaluated. As a result, it was confirmed that the sliding parts having the hard carbon film shown in Examples 1 to 8 showed excellent low friction and wear resistance characteristics.
(Molecular dynamics simulation)
The mechanism that keeps a stable coefficient of friction for the trace amount of element X added to the first layer is thought to have the effect of accelerating the reaction of the carbon body on the surface of the counterpart steel part. .

In the present invention, in order to elucidate the transfer behavior of carbon bodies on the surface of steel parts, the binding energy of molecular adsorption was estimated by molecular dynamics simulation. Assuming C (CH _{3) 3} as the simplest molecular structure of amorphous carbon released between sliding parts by self-lubricating reaction, C (CH _{3) 3} and B (CH _{3) 3} , Cr (CH _{3 ) 3} and Ti (CH3 _{) 3} were compared. In general, iron oxide is formed on the surface of steel parts exposed to the atmosphere. In this experiment, assuming that the iron oxide is exposed on the surface of the part, -O-Fe ( The binding energy with OH) ₅ was calculated and the absolute values of C—O and X—O were compared. In order to reduce the calculation load of the binding energy, the iron oxide was replaced with the iron hydroxide, and it was found that the result of the iron oxide shows the same tendency as the iron hydroxide. Compared to C—O, the absolute values of the binding energies of B—O, Cr—O and Ti—O were large, indicating that they were strongly adsorbed.

1 ... hard carbon film, 11 ... first layer (surface layer), 12 ... second layer, 2 ... base material,
3 ... Parts, 4 ... Steel parts
501 ... Plunger, 502 ... Oil seal, 503 ... Cylinder, 504 ... Lifter, 505 ... Cam, 506 ... Fuel flow path, 507 ... Suction side valve, 508・ Discharge side valve
601 ... Valve lifter, 602 ... Cam, 603 ... Valve, 604 ... Intake duct (or exhaust duct), 605 ... Combustion chamber
701 ... Plate test piece, 702 ... Ring test piece, 703 ... Heater, 704 ... Torque measuring arm, 705 ... Load cell, 706 ... Test chamber wall, 707 ..Water for keeping warm

Claims

In sliding parts with parts with hard carbon film and steel parts in sliding contact with them,
The hard carbon film includes at least a first surface layer and a second layer therebelow, and the first layer includes at least one element X (B, Cr, Ti) and C and H, The second layer includes at least one of the elements X contained in the first layer, and the first layer has a lower element concentration of the element X than the second layer. .
2. The element X according to claim 1, wherein the element X is Cr, and the Cr concentration of the first layer is 0.05 atomic% or more and 0.12 atomic% or less when the total of Cr and C contained in one layer is 100%. The sliding component, wherein the second layer has a Cr concentration of 0.24 atomic% or less.
The sliding according to claim 1, wherein the hardness of the first layer is 15 GPa or less and the hardness of the second layer is 24 GPa or more when measured by an instrumented indentation hardness test. parts.
2. The sliding component according to claim 1, wherein the element X is B, and the second layer further includes N.
The sliding part of claim 1 is used in a valve lifter, tappet, adjusting shim, cam, camshaft, rocker arm, piston, piston pin, piston ring, timing gear, timing chain, and fuel supply system disposed in an internal combustion engine. A sliding part characterized by being an injector, a plunger, a cylinder, a cam, or a vane.