KR101203776B1 - Method for surface treatment of valve lifter - Google Patents

Abstract

The present invention relates to a valve lifter and a surface treatment method thereof, and more particularly, to a DLC coating method of a valve lifter using a solid graphite target and a solid SiC target.
Accordingly, the present invention, the first step of carburizing and tempering the base material surface; A second step of polishing the tempered base material with a surface roughness Ra of 0.01 to 0.04 µm; A third step of forming a 0.3-1.0 μm thick Me-DLC layer formed by sputtering any one selected from the group of W, Cr, Ti, and Mo after forming an interfacial layer of metal on the polished base material; Si content on the Me-DLC layer is 3-10 atomic% It provides a valve lifter surface treatment method comprising a; 4th step of forming a Si-DLC layer having a hydrogen content of 5 to 12 atomic% to a thickness of 1.0 ~ 2.0㎛.

Description

Valve lifter surface treatment method {METHOD FOR SURFACE TREATMENT OF VALVE LIFTER}

The present invention relates to a valve lifter and a surface treatment method thereof, and more particularly, to a DLC coating method of a valve lifter using a solid graphite target and a solid SiC target.

In general, the valve lifter functions to change the rotational movement of the camshaft up and down and is mainly made of alloy cast iron or carbon steel.

1 is a view showing a part of the configuration of a conventional valve train system for an internal combustion engine, Figure 2 is a view showing the microstructure of the DLC layer of the conventional valve lifter surface coating layer, Figure 3 is a view of the conventional valve lifter surface coating layer Schematic diagram of equipment used for formation.

As shown in FIG. 1, the valve lifter 20 has a cylindrical structure, and friction is constantly generated on the upper surface 21 to which the rotating camshaft 10 contacts. In order to reduce such friction, the surface of the valve lifter 20, in particular, the upper surface 21 is mirror-machined, diamond like carbon (DLC) coating or CrN (Chromium Nitride) coating.

DLC is an amorphous carbon compound with excellent physicochemical properties such as high hardness, low coefficient of friction, wear resistance, electrical insulation, light transmittance and chemical stability.

Recently, DLC, which maximizes low friction characteristics, is coated on the upper surface of a valve lifter for improving fuel efficiency of a vehicle (Patent Application No. 2008-70306).

Conventional physical vapor deposition (PVD) DLC coating technology forms a plasma using Ar ions, and then sputters and coats a solid graphite (C) target (see FIG. 3).

In some cases, PACVD (Plasma Assisted Chemical Vapor Deposition) is used to synthesize DLC by high temperature pyrolysis of hydrocarbons (eg, C ₂ H ₂ , CH _4, etc.) and gases such as Ar and H ₂ .

DLC, however, exhibits thermal degradation or graphitization in which diamond structure (sp3 bond) is changed to graphite structure (sp2 bond) due to the molecular dissociation of hydrogen at a temperature higher than 400 ° C, resulting in reduced hardness and wear resistance. This has the disadvantage of being weakened.

The problem of DLC is that the DLC becomes incomplete when it is operated for a long time because the instantaneous contact temperature between the cam and the tappet (upper surface of the valve lifter) that is driven under the condition that the engine is gradually increased and the lubrication condition is more severe can occur. Durability can be weakened.

The greater the amount of hydrogen in the DLC, the greater the amount of hydrogen released at high temperatures, and therefore, the thermal stability of the PACVD DLC is more disadvantageous than the PVD DLC.

As a result, in order to obtain DLC having sufficient durability at high temperature, it is necessary to develop a new DLC coating method using PVD instead of PACVD.

The present invention has been invented to solve the above problems, while maintaining the low friction characteristics of the DLC coating to add a high frictional resistance and low heat resistance Si to enhance the high temperature heat resistance, for this purpose solid and solid graphite target simultaneously An object of the present invention is to provide a valve lifter using PVD (Physical Vapor Deposition) method for coating Si-DLC using a SiC target, and a surface treatment method thereof.

In order to achieve the above object, the present invention, an interface layer formed by sputtering a metal target on the surface of the carburized and the base material; Me-DLC layer having a thickness of 0.3 ~ 1.0㎛ formed on the interface layer while sputtering any one selected from the group of W, Cr, Ti, Mo; A valve lifter comprising: a Si-DLC layer having a thickness of 1.0 to 2.0 μm on the Me-DLC layer and having a Si content of 3 to 10 atomic% and a hydrogen content of 5 to 12 atomic%; to provide.

Preferably, the carburizing-treated base material is characterized in that the surface roughness Ra 0.01 ~ 0.04㎛.

Also preferably, the interface layer is characterized in that the coating layer formed by sputtering any one selected from the group of Cr, Ti.

More preferably, the Si-DLC layer has a SP 3 bond fraction of 60 to 70% It is characterized in that the hardness is 20 ~ 30GPa.

On the other hand, the present invention, the first step of carburizing and tempering the surface of the base material; A second step of polishing the tempered base material with a surface roughness Ra of 0.01 to 0.04 µm; A third step of forming a 0.3-1.0 μm thick Me-DLC layer formed by sputtering any one selected from the group of W, Cr, Ti, and Mo after forming an interfacial layer of metal on the polished base material; Si content on the Me-DLC layer is 3-10 atomic% It provides a valve lifter surface treatment method comprising a; 4th step of forming a Si-DLC layer having a hydrogen content of 5 to 12 atomic% to a thickness of 1.0 ~ 2.0㎛.

Preferably, the Si-DLC layer is characterized in that the SP3 bonding fraction is 60 ~ 70% and the hardness is 20 ~ 30GPa.

More preferably, the Si-DLC layer is formed by sputtering the solid graphite target and the solid SiC target at the same time, the control of the Si content is made by adjusting the cathode power (cathode power) of the power supply to the SiC target and the SP3 bond The fraction is controlled by adjusting the amount of acetylene supplied and the bias voltage applied to the valve lifter mounting jig.

More preferably, the interface layer is formed by sputtering any one target selected from the group of Cr and Ti.

In addition, the present invention is a valve lifter formed with a coating layer on the surface,

The top coating layer of the coating layer provides a valve lifter, characterized in that the Si content of 3 to 10 atomic%, hydrogen content of 5 to 12 atomic%, and the SP3 bonding fraction of 60 to 70% Si-DLC layer.

Preferably, the Si-DLC layer is characterized in that the thickness is 1.0 ~ 2.0㎛ and the hardness is 20 ~ 30GPa.

According to the present invention, SiC having high hardness and high temperature wear resistance can be directly formed in the DLC, and the hydrogen content can be kept low at 5 to 12 atomic%, which is advantageous for low friction and can increase the hardness of the DLC.

In addition, since the amount of Si can be adjusted by adjusting the number of SiC targets or the cathode power of the power supply applied to the SiC target, the process is simple.

1 is a view showing a part of the configuration of a conventional valve train system for an internal combustion engine;
2 is a view showing the microstructure of the DLC layer of the conventional valve lifter surface coating layer,
3 is a schematic view of the equipment used to form a conventional valve lifter surface coating layer,
4 is a view showing the structure of the surface coating layer of the valve lifter according to an embodiment of the present invention,
5 is a view showing a microstructure of the Si-DLC layer shown in FIG.
6 is a view showing a bonding structure of the Si-DLC layer shown in FIG.
FIG. 7 is a schematic diagram of PVD equipment used to form the Si-DCL layer shown in FIG. 4;
8 is a schematic flowchart illustrating a process of forming a surface coating layer of a valve lifter according to an embodiment of the present invention;
9 is a graph showing a comparison of the friction test results for the valve lifters according to the Examples and Comparative Examples of the present invention,
10 is a graph showing the hardness before and after the heat treatment for the valve lifters according to the embodiment and comparative example of the present invention,
11 is a graph showing the results of Raman analysis before and after heat treatment of the valve lifter according to the embodiment of the present invention.

The present invention relates to a coating process of DLC added with Si excellent in the low friction properties and heat resistance in order to enhance the high temperature heat resistance while maintaining the low friction properties of the DLC coating.

According to the present invention, fine Si and SiC (silicon carbide) particles are formed in the DLC formed on the upper surface 21 of the valve lifter 20. The existing DLC is due to Si having excellent lubricity and SiC having high hardness and good heat resistance. Compared to this, the friction can be improved by about 10% while improving the high temperature wear resistance and stability.

The present invention basically uses a DLC coating method using the PVD method, but for the addition of Si, DLC coating is added to Si using a solid graphite target and a solid SiC target simultaneously, not a gas.

Therefore, the present invention can directly form SiC having high hardness and high temperature wear resistance in DLC, and can maintain hydrogen content as low as 5 to 12 atomic%, which is advantageous for low friction and can increase the hardness of DLC.

Hereinafter, with reference to the accompanying drawings will be described in detail the valve lifter and the surface treatment method of the present invention.

As shown in FIG. 4, the valve lifter 20 according to the present invention has a high hardness surface coating layer which prevents high temperature graphitization and has excellent heat resistance while maintaining low friction characteristics on its outer surface, particularly the upper surface 21. do. The surface coating layer may be formed directly on the surface of the valve lifter, or may be formed on a shim (SHIM) separately padded on the upper surface 21 of the valve lifter 20 in contact with the camshaft 10.

In the embodiment of the present invention, the surface coating layer of the valve lifter is composed of coating layers such as an interfacial layer, a buffer layer (Me-DLC layer), and a Si-DCL layer that are sequentially stacked on a carbonitrided base material.

4 to 8 will be described with respect to the surface treatment method of the valve lifter and the coating layers formed on the surface of the valve lifter according to the present invention.

First, prior surface treatment is performed prior to surface coating of the valve lifter.

Carburizing and carburizing is performed to cure and stabilize the base material on which the coating layers are formed. That is, after carburizing and carburizing the surface of a base material, it tempers at 200-250 degreeC.

The surface of the carburizing-precipitated base material is polished to a surface roughness Ra of 0.01 to 0.04 μm. If the surface roughness of the base material is less than 0.01㎛ has a problem that the roughness is rather increased due to the surface coating of the base material to increase the cost, and when the surface roughness exceeds 0.04㎛, the friction reduction effect by the coating layer is There is a problem falling.

For polishing of the surface of the base material, methods such as buffing, vibration finishing (VF), super finishing (SF), and the like may be used.

Next, coating is performed on the surface of the base material on which the pre-surface treatment is completed.

In order to improve adhesion between the base material and the coating layers stacked thereon, an adhesion layer is formed on the surface of the pre-treated surface of the base material. Cr, Ti, etc. can be used for formation of such an interfacial layer, and the effect of the Cr coating layer formed by sputtering Cr target especially is excellent.

A metal-containing DLC layer (hereinafter referred to as "Me-DLC layer") using a reactive sputtering method of adding acetylene (C ₂ H ₂ ) to supply a carbon source during the sputtering process using a metal target on the interface layer. To form a buffer layer. That is, the Me-DLC layer is formed by sputtering a metal target while supplying acetylene as a reaction gas to the surface of the base material, wherein W, Cr, Ti, Mo, and preferably W are used as the metal target.

The Me-DLC layer is deposited with a thickness of 0.3-1.0 μm to serve as a buffer layer that complements the brittleness of the upper DLC layer (ie, Si-DCL layer), improves impact resistance, and gives fatigue resistance to long-term fatigue. do.

If the thickness of the Me-DLC layer is less than 0.3㎛ the impact resistance and fatigue resistance is not sufficient, if the thickness of the Me-DLC layer exceeds 1.0㎛ Me-DLC layer formation effect due to the increase of the residual stress itself Falls.

A low friction property is substantially exhibited on the Me-DLC layer, and a Si-DLC layer having excellent high temperature heat resistance is formed to a thickness of 1.0 to 2.0 μm. If the thickness of the Si-DLC layer is less than 1.0 μm, there is a problem that the Si-DLC layer is worn away during the initial break-in of the internal combustion engine, and the thickness of the Si-DLC layer is If it exceeds 2.0 μm, there is a problem of peeling due to an increase in the residual stress of the coating.

The Si-DLC layer is formed by sputtering a solid graphite target and a solid SiC target simultaneously while supplying a small amount of acetylene.

As shown in FIG. 6, the Si-DLC layer has a mixed structure of SP2 and SP3 bonds in which carbon, hydrogen, or Si is bonded to carbon, and has the best low friction property when the fraction of the SP3 bond is 60 to 70%.

If the fraction of the SP3 bond is less than 60%, the hardness of the Si-DLC layer drops sharply and wear of the valve lifter surface occurs. If it exceeds 70%, the inherent low friction characteristic of the DLC layer is significantly reduced.

The SP3 binding fraction can be controlled by supplying finely adjusted acetylene and adjusting the bias voltage applied to the jig in which the valve lifter is mounted.

The fraction of SP 3 bonds in the Si-DLC layer increases with hydrogen supply and tends to decrease with increasing bias voltage. Therefore, considering only the low friction characteristics of the Si-DLC layer, less acetylene and higher bias voltage.

However, since the hardness of the Si-DLC layer also depends on the bias voltage and becomes the maximum value at a specific bias voltage, the Si-DLC layer has excellent wear resistance and low friction characteristics only when the optimum value is obtained in consideration of the hardness and the SP3 bonding fraction. A DLC layer can be obtained.

In addition, the Si content in the Si-DLC is 3 to 10 atomic%, and when the Si is less than 3 atomic%, the low friction and high temperature heat resistance effects of the Si-DLC due to the addition of Si are not sufficiently large, and when the Si is 10 atomic% or more, the hardness is There is a problem that a sharp decrease in wear resistance deteriorates.

The control of the Si content is possible by controlling the cathode power of the power supply across the SiC target.

Looking at the PVD equipment for the formation of the Si-DLC layer with reference to Figure 7, a solid graphite target and a solid SiC target is installed in the vacuum chamber and a valve lifter is installed at a distance spaced therefrom. Cathode power is applied to the graphite target and the SiC target, and the bias voltage (-Vsb) is also applied to the jig in which the valve lifter is mounted. One side of the vacuum chamber is supplied with Ar for generating sputtering by hitting the negatively biased graphite target, and the other side is supplied with acetylene for hydrogen control.

By adjusting the bias voltage and the amount of acetylene applied to each target and the jig using the above equipment, the fraction of the SP3 bond in the Si-DCL is controlled to be 60 to 70%. 5 to 12 atomic percent. At this time, the hardness of the Si-DLC layer is about 20 to 30 GPa.

That is, the Si-DCL will contain 60 to 70% of the SP3 bond fraction, 3 to 10 atomic% of Si, and 5 to 12 atomic% of hydrogen.

In other words, the valve lifter surface-treated by the above process is an interface layer formed by sputtering any target selected from the group of Cr and Ti on the surface, in particular, on the surface of the carburizing-precipitated base material, W on the interface layer. 0.3-1.0 μm thick Me-DLC layer formed by sputtering any target selected from the group of Cr, Ti, Mo, and 1.0-2.0 μm thick on the Me-DLC layer, and Si is 3-10 atoms A surface coating layer containing a Si-DCL layer containing% and having an SP3 bonding fraction of 60 to 70% is formed.

In order to check the low friction characteristics of the valve lifter coated by the above surface treatment method, three valve lifters of the same material were manufactured, and each of them was subjected to the surface treatment as shown in Table 1 below, and then subjected to friction under the conditions of Table 2 Torque experiment was performed, and the results are shown in FIG.

In Comparative Example 1, only the above-described pre-surface treatment was carried out, and Comparative Example 2 completed the pre-treatment and multiple coating (buffer layer, Me-DLC layer, DLC layer) treatment by DLC coating by conventional PVD method.

As shown in FIG. 6, the Example according to the present invention showed a lower friction torque curve (smaller friction torque value) than Comparative Examples 1 and 2. In particular, compared to Comparative Example 1 without a coating treatment, the friction torque of the Example was 33% lower at 2,000rpm, compared to Comparative Example 2, DLC coating by PVD method, the friction torque of the Example was 10% lower at 2,000rpm.

As a result, the Si-DLC coating method for the valve lifter according to the present invention is excellent in low friction effect, and has been shown to help improve fuel efficiency by reducing frictional losses of the engine.

On the other hand, in order to confirm the stability and wear resistance of the valve lifter coating layer at a high temperature, the valve lifter surface treated by Comparative Example 2 and Example was heat-treated at 400 ° C. for 20 hours, and then hardness measurement and Raman analysis of the coating layer were performed. 10 is a change in hardness of Comparative Example 2 and Example before and after the heat treatment.

In Comparative Example 2, the hardness before the heat treatment was 30 GPa, but the hardness decreased to 18 GPa after the heat treatment. In the half side example, the hardness of 28 GPa before the heat treatment and the hardness of 27 GPa after the heat treatment showed little change in hardness before and after the heat treatment.

In general, the hardness is known to be proportional to the wear resistance, it can be guessed that the wear resistance of the embodiment with little change in hardness compared to Comparative Example 2 that the hardness decreases badly at high temperatures.

In addition, Raman analysis generally displays the unique information of the material because it measures the vibration energy inherent in the molecular bond structure.

11 is inde Raman analysis results of the heat treatment before and after the coating layer, since the diamond in the case of the intermediate image of the graphite DLC G peak of 1350cm D peak (peak) of ^-1 and 1580cm ^-1 are mixed amorphous phase appears and broad (broad) a shape Shows a spectra with

In Comparative Example 2, the separated portion of the D peak and the G peak is found after the heat treatment, which means that a disordered fine graphite phase is gradually formed in the DLC, thereby graphitizing the DLC. On the other hand, in Example, there was almost no change in the peak even after the heat treatment, and it was confirmed that the coating layer had the properties before the heat treatment.

As a result, it can be seen that the Si-DLC coating according to the present invention has strong resistance to DLC graphitization and excellent high temperature stability.

In the present invention, by using a solid graphite target and a solid SiC target instead of a gas to form a DLC added to Si, the hardness is high due to the low hydrogen content of Si-DLC (5-12 atomic%) and high bonding energy -The coefficient of friction of DLC is low and wear resistance is excellent.

In addition, the present invention has a low hydrogen content in the Si-DLC high resistance to graphitization of the Si-DLC at a high temperature and can improve the high temperature stability due to the fine SiC particles.

In addition, since the amount of Si can be adjusted by adjusting the SiC target quantity or the cathode power applied to the SiC target, the process is simple.

While the invention has been shown and described with respect to preferred embodiments thereof, the invention is not limited to these embodiments, and various modifications may be made by those of ordinary skill in the art to which the invention pertains. It includes all forms of embodiments.

10: camshaft
20: valve lifter
21: upper surface of the valve lifter

Claims (10)

delete delete delete delete Carburizing and tempering the surface of the base material;
A second step of polishing the tempered base material with a surface roughness Ra of 0.01 to 0.04 µm;
A third step of forming a 0.3-1.0 μm thick Me-DLC layer formed by sputtering any one selected from the group of W, Cr, Ti, and Mo after forming an interfacial layer of metal on the polished base material;
Si content on the Me-DLC layer is 3-10 atomic% A fourth step of forming a Si-DLC layer having a hydrogen content of 5 to 12 atomic percent to a thickness of 1.0 to 2.0 μm;
Including,
The Si-DLC layer is formed by sputtering a solid graphite target and a solid SiC target at the same time, the Si content is controlled by controlling the cathode power applied to the SiC target and the SP3 binding fraction is controlled for the acetylene supply and valve lifter mounting A valve lifter surface treatment method comprising adjusting a bias voltage applied to a jig.
The method according to claim 5,
The Si-DLC layer is a valve lifter surface treatment method, characterized in that the SP3 bonding fraction is 60 ~ 70% and the hardness is 20 ~ 30GPa.
delete The method of claim 5, wherein the interface layer is formed by sputtering any one target selected from the group of Cr and Ti.
delete delete

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