DE10213661A1 - Process for producing a coating of a metallic substrate - Google Patents

Abstract

A method for producing a coating of a metallic substrate in a recipient is proposed. The substrate is etched in a plasma on the surface using an inert gas and then coated using a plasma-assisted CVD method. An oxygen-containing gas is at least temporarily added to the inert gas.

Description

State of the art

The invention relates to a method of manufacture a coating of a metallic substrate according to the im The preamble of claim 1, the more precisely defined type out.

Coatings of metallic substrates in the form of Carbon-containing coatings are wide in the art spread and exhibit properties such as a very high Hardness, high wear resistance, chemical inertness, Biocompatibility, a low coefficient of friction, an optical transparency in the infrared range and / or something similar.

Such coatings include amorphous Carbon layers, as diamond-like layers or DLC (diamond like carbon) layers, or as amorphous DLC layers Layers known and can for example as Wear protection of data carriers, anti-friction coating of Bearing elements, hard material layer on tools, Wear protection layer of components in the automotive sector, inert Covering medical implants or as optical Layer used on lenses, windows and mirrors become.

A method of the type mentioned in the introduction is from DE 30 47 888 C2 known and used to produce a Carbon-containing coating of workpieces, for example cutting razor blades or saws. at This process creates the surface of the workpiece in one Recipients with an inert gas, for example with argon, etched. Then there is first an intermediate layer and then a layer of carbon on the surface applied. The carbon layer, which has a thickness between 10 nm and has 10 microns, is produced in that Acetylene or ethylene introduced into the recipient and with Using a plasma on the surface of the workpiece is deposited. The intermediate layer provides an adhesive layer which by a sputtering method, d. H. a so-called PVD process (physical vapor deposition) is deposited.

The disadvantage of this method is that it is small Deposition speed of the adhesive layer, the high consumption costs through the use of so-called targets, from which the Adhesive layer is produced in the so-called sputtering, high investment costs for the sputter cathodes and necessary power supplies and the time-consuming maintenance of the Sputter cathodes, which consists of a change of target.

It has also been suggested as the adhesive layer to form silicon-containing adhesive layer by a so-called CVD (chemical vapor deposition) process is generated. at this process, the adhesive layer is made directly from a gaseous precurser formed after a plasma-assisted process is deposited on the component surface.

From DE 33 16 693 C2 a method for producing amorphous carbon layers on substrates is known, in which a glass substrate is coated in a plasma without substrate pretreatment in such a way that a silicon-containing gas is first introduced into a recipient and this is subsequently converted by means of plasma support and for the production an adhesion-promoting coating is deposited on the surface of the substrate. To increase the hardness of the adhesion-promoting coating, the so-called adhesive layer, 10 % by volume to 50% by volume of an oxygen-containing gas or else pure oxygen are added to the silicon-containing gas. By throttling the supply of the silicon-containing gas and adding gaseous hydrocarbon compounds, an amorphous carbon layer is deposited on the adhesive layer in a next process step.

From US 5 190 807 a wear-resistant, polymer-like product known as an adhesion promoter Layer a polymer-like polysiloxane intermediate layer is applied directly to a substrate, for example consists of polycarbonate or polyacrylic. On the Polysiloxane intermediate layer are further intermediate layers, for example made of silicon dioxide, on which again a diamond-like carbon layer as Wear protection is applied. To increase the liability of the Layers on the polymer substrate will be the substrate before Coating a plasma etching process with a Ion beam subjected to an inert gas, the hydrogen or Oxygen ions can be added. This pretreatment is used in particular to remove hydrocarbons and contamination by alkali metals and others Additives that adhere to the surface of the polymeric substrate have accumulated.

EP 0 600 533 B1 describes a method for coating a substrate made of steel, iron or an iron alloy known with diamond-like carbon. With this The substrate is processed using a plasma etching process pretreated, in which the substrate in a plasma of argon and Hydrogen is etched. Then a thin one Silicon intermediate layer applied in that the substrate exposed to gaseous silane. Following that gradually added methane, so that diamond-like Carbon deposits on the silicon interlayer.

The use of this known method is disadvantageous of the gas silane, which is only under high Safety precautions can be used.

From US 5 653 812 is a method for coating elongated, metallic components, such as drills and pipes, known. In this process, the components are one Subjected to plasma etching with an inert gas such as Argon, is carried out so that the surface of the Components cleaned of hydrocarbon residues and oxides and is activated. In a subsequent step an adhesion promoting layer using a applied organic silicon monomer. After that will be on the adhesion promoting layer carbon-containing coating deposited.

A method to improve the layer adhesion of hard, carbon-containing coatings on steel substrates known from EP 0 856 592 A1. With this procedure to improve the liability of the under strong Compressive residual stress, carbon-containing layer applied the first adhesive layer with a nanocomposite interpenetrating networks of amorphous Hydrocarbons and amorphous silicon oxide exist. The metallic substrate is previously a plasma etching process subjected to ions of an inert gas such as argon, is shot at.

The disadvantage of this method is that it is necessary for good layer adhesion, to apply numerous, multilayer coating systems. At a the total layer thickness is the available Thickness of the functionally relevant, a DLC layer performing layer limited.

From US 5 771 873 is a method for applying a carbon-containing, serving as protection against coking Coating known to components in an engine combustion chamber to be ordered. The process involves a chemical Cleaning by a plasma etching process in an argon Atmosphere followed a vacuum chamber. Thereupon will a silicon-containing hydrocarbon layer of a thickness of 0.5 µm applied. Then one carbon-containing layer of about 2 microns applied, which also Contains silicon to increase the anti-coking effect guarantee. However, the silicon content reduces that Layer hardness. Also the wear behavior of the layer system adversely affected.

In all of the aforementioned processes for the production of Adhesive layer systems in which an intermediate layer is not able to form metal-containing ones Adhesive layers of equivalent layer adhesion are generated. Especially considering the very sensitive Rockwell adhesion test procedure is not a layer system known that a comparable liability under Guaranteed reproducible conditions for large-scale production without that other disadvantages, such as large adhesive layer thicknesses, complex multi-layer systems or reduced layer hardness of carbon-containing coating can be accepted would.

Advantages of the invention

The inventive method for producing a Coating a metallic substrate with the features according to the preamble of claim 1, in which Process added an oxygen-containing gas to the inert gas has the advantage that the admixture of the oxygen-containing gas to the inert gas at the Pre-cleaning of the substrate using the plasma etching process Subsequent layer liability after the CVD process applied layer or layers significantly improved and adhesion to non-metallic adhesive layers can be achieved with that of metallic Subbing layers, e.g. B. consist of chrome, comparable is. This is particularly with the help of a Rockwell adhesion tests detectable.

By using the method according to the invention, a Adhesion of carbon-containing coatings to metallic Substrates can be achieved that meet the high requirements it suffices to protect the wear during component coating of tools and components. Especially when high demands are placed on the layer adhesion of a carbon-containing coating is also the use of silicon-containing adhesive layer systems.

The fact that when the coating is applied only plasma-assisted CVD processes are used and PVD mechanisms are dispensed with is the Complexity of the process or the plant advantageously low.

The oxygen-containing gas which is added to the inert gas can be pure oxygen O ₂ or also a gas such as ozone O ₃ , nitrogen oxide N ₂ O or water H ₂ O which comprises oxygen.

In a preferred embodiment of the method according to the invention, a layer system is applied to the surface of a metallic substrate, which consists for example of a stainless steel alloy, after the plasma etching process with argon and oxygen, which consists of silicon atoms implanted in the substrate surface, an adhesive layer which Deposition of silicon-containing monomers is produced, there is a transition layer with a decreasing silicon content and increasing carbon content, and a so-called DLC layer, which forms the top layer of the coating system. The DLC layer is an X-ray amorphous layer with sp ³ -hybridized carbon atoms. The DLC layer therefore has a so-called short-range diamond order.

The method according to the invention is particularly suitable a metallic substrate with a so-called DLC Layer using a silicon-containing adhesive layer to provide. With such a system, the Adhesion strength compared to a system without the use was etched by oxygen in a plasma from a Adhesive strength between 3.5 and 5 on an adhesive strength be reduced between 2.0 and 3.

The method according to the invention can be carried out in such a way that the substrate, optionally after wet chemical cleaning of oil residues or the like, is placed on a vacuum-compatible holder in a vacuum chamber, which is then evacuated to a residual gas pressure of less than 10 ^-1 mbar.

The substrate is then etched in a plasma. The Plasma can by means of direct voltage discharge, the So-called DC method, by means of frequency excitation Components, the so-called medium frequency method, by means of Radio frequency excitation of the components, the so-called RF process, or by coupling microwaves and Generation of a microwave plasma, the so-called MW process.

In this so-called plasma etching or cleaning process, a negative voltage, the so-called bias voltage, is applied to the substrate in order to accelerate positively charged ions onto the surface of the substrate. When the charged ions impact, impurities are removed from the surface by the sputtering effect. The selected bias voltage, which can be between -50 V and more than -1000 V, depends on the selected plasma process. The pressure in the plasma etching process is chosen so that the plasma discharge is stable and therefore dependent on the selected plasma process. A pressure between 10 ^-4 mbar and 10 mbar has proven to be suitable.

Preferred inert gases in the plasma etching process Noble gases, e.g. argon, helium and neon, individually or used as a mixture. For cost reasons and however, argon is preferred due to the high atomic mass used. Hydrogen can also be added to the inert gas be admixed to the formation of oxides on the metallic Suppress substrate surface.

The oxygen-containing gas, which according to the invention during the Plasma etching is added to the inert gas, can Share between 1% and 80%, preferably a share of 10% to 50%. The addition of the oxygenated Gas can be Process or only temporarily.

A particularly positive effect can be achieved if the plasma etching process first with pure argon and then carried out with an argon-oxygen mixture typically for a period of between 1 min and 60 min, preferably for a duration between 5 min and 20 min.

Following the plasma etching process, the substrate is subsequently coated with a plasma-assisted CVD process. This can be done in one or more substeps become.

For example, a silicon-containing gas is first introduced into the vacuum chamber to produce an adhesion-promoting, silicon-containing layer. The silicon-containing gas is preferably admitted without switching off the plasma burning in the preceding process step, ie the plasma etching, in order to obtain a transition which is as free of faults and adheres as possible. In this method step, a high negative voltage is preferably generated on the surface of the substrate, which can be, for example, between -100 V and -600 V, so that silicon atoms are implanted in the metal grid of the substrate and good interlocking of the silicon-containing adhesive layer with the substrate is achieved becomes. The silicon-containing gas is introduced into the vacuum chamber at a pressure between 10 ^-4 mbar and 1 mbar.

In principle, all silicon-containing monomers can be used as the silicon-containing gas. However, the monomers silane (SiH ₄ ), tetramethylsilane TMS (SiC ₄ H ₁₂ ), tetraethoxysilane TEOS (SiO ₄ C ₈ H ₂ O), hexamethyldisiloxane HMDSO (Si ₂ OC ₆ H ₁₈ ) or hexamethyldisilane HMDS (Si ₂ C ₆ H ₁₈ ) is used, the monomers tetramethylsilane, tetraethoxysilane and hexamethyldisiloxane being particularly suitable, since these are inexpensive to obtain and have a sufficiently high vapor pressure for the process.

According to a preferred embodiment of the method the invention is then the silicon-containing gas a hydrocarbonaceous gas is added to a well adhesive transition from the resulting silicon-containing Adhesive layer on a hard, diamond-like Achieve carbon layer in a subsequent, further process step described below is applied.

As the hydrocarbon-containing gas, methane (CH ₄ ), ethane (C ₂ H ₆ ), ethene (C ₂ H ₄ ), ethyne (C ₂ H ₂ ), cyclohexane (C ₆ H ₁₂ ), benzene (C ₆ H ₆ ) and / or other hydrocarbons can also be used.

Following this, the addition of the silicon-containing Gases stopped and the coating with pure Hydrocarbon are continued, so that a so-called DLC Layer is generated. It is preferred to add the silicon-containing gas is continuously reduced.

A layer of high hardness containing hydrocarbons can in particular to be deposited when as hydrocarbon-containing gas ethyne is used.

Hydrocarbons can also be used in addition to carbon and hydrogen heteroatoms, such as for example nitrogen, oxygen, silicon or fluorine, contain. The heteroatoms give the resulting diamond-like carbon layer or DLC layer special Properties, such as an increased Temperature stability, increased abrasive wear on a counter body, a low coefficient of friction, a change in Wetting behavior, an improvement in adhesive behavior or an improvement in optical transparency.

Alternatively or additionally, the heteroatoms can be formed Elements also added via added gases become.

It is also possible to add the above Properties of the diamond-like carbon layer thereby achieve that after plasma-assisted deposition of a pure hydrocarbon coating one or several additional layers are applied, namely with the addition of additional gases or by use of hydrocarbons, in addition to carbon and Hydrogen heteroatoms, like the above elements, contain.

Depending on the application, this can be done with an inert gas and plasma-etched an oxygen-containing gas A layer system can be applied from the substrate surface one or more layers. For example, it is conceivable that by means of a deposited silicon-containing gas and a layer DLC layer is deposited directly on the substrate. In in this case the adhesive layer would be eliminated.

Basically, with the method according to the invention all metallic components are coated. Especially However, it is suitable for components made of steel, iron or also made of stainless steel alloys that are used in practice have a wide range of applications.

The method has proven to be particularly advantageous shown the invention when nozzle needles for common rail Injectors, rollers of common rail injector systems and other components of diesel injection pumps coated become.

Further advantages and advantageous configurations of the Subject of the invention are the description of Drawing and the claims can be found.

An embodiment of the object according to the invention is shown schematically simplified in the drawing and is explained in more detail in the following description.

Show it

FIG. 1 shows a layer system, which is manufactured by the method according to the invention; and

FIG. 2 is a diagram illustrating the adhesive strength of samples that have been subjected to different etching processes.

Description of the embodiment

In Fig. 1, a layer system is shown, which is prepared by the inventive method. This layer system comprises four layers, which are applied to a substrate made of a stainless steel alloy, and forms a coating of a nozzle needle of a common rail injector, not shown here.

The layer system shown in Fig. 1 comprises a layer 10 of silicon atoms which are implanted in a surface of the substrate made of the stainless steel alloy, an adhesion-promoting layer 20 with a thickness between 20 nm and 100 nm, which consists of an amorphous silicon layer with carbon and There are hydrogen components, the silicon component in layer 20 being between 20% and 70%.

Furthermore, the layer system comprises a layer 30 with a thickness between 100 nm and 200 nm, which is arranged on the layer 20 and is formed as a transition layer, which consists of amorphous silicon with carbon and hydrogen components and components of diamond-like carbon. In layer 30 , the proportion of diamond-like carbon increases in the direction facing away from layer 20 . The proportion of silicon in layer 30 is between 15% and 50%. The amorphous silicon layers 20 and 30 with carbon and hydrogen components represent chemically cross-linked polymers.

The layer system shown in FIG. 1 comprises, as the top layer, a layer 40 with a thickness of 1 μm to 3 μm, which is designed as a so-called DLC layer and represents the actual functional layer of the layer system. The DLC layer 40 represents a hydrocarbon-containing layer, which can optionally have silicon components. It is also conceivable to produce the DLC layer free of hydrogen. The thickness of the DLC layer 40 or that of the layers 20 and 30 can be controlled.

The layer system shown in FIG. 1 is produced in the manner described below.

In a first process step, what is to be coated Component, d. H. the one made of a steel alloy Substrate, wet-chemically cleaned.

Then the substrate is vacuum-compatible Mounted and together with this in a Vacuum chamber introduced.

The vacuum chamber is then evacuated to a residual gas pressure of approximately 10 ^-4 mbar.

In a subsequent process step, the surface of the substrate is etched in a plasma. The plasma is generated by means of direct voltage discharge. A bias voltage of here -1000 V is applied to the substrate so that positively charged ions are accelerated onto the surface of the substrate and so-called plasma cleaning takes place. The pressure during the plasma cleaning is chosen so that the plasma discharge is stable. In the present case, the pressure is approximately 10 ^-2 mbar. In the present case, argon is used as the inert gas, which is ionized and accelerated to the surface of the substrate. Argon is mixed with hydrogen to suppress the formation of oxides on the surface of the substrate. Furthermore, oxygen is added to the inert gas as an oxygen-containing gas. The concentration of oxygen in the gas mixture is about 40%.

The plasma etching process is controlled so that the Vacuum chamber first pure argon and then that Argon-oxygen mixture supplied. The plasma etching takes place here for one Duration of 15 minutes.

In a subsequent process step, a silicon-containing gas, namely tetramethylsilane, TMS, is introduced into the vacuum chamber. In this process step, a high negative voltage of several hundred volts is generated on the surface of the substrate, so that silicon atoms are implanted in the metal grid of the substrate, as a result of which the silicon-containing, adhesion-promoting layer produced in this process process is well interlocked with the substrate. Layers 10 and 20 of the layer system shown in FIG. 1 are thus formed.

In a subsequent process step, a hydrocarbon-containing gas, namely ethyne, is additionally added to the silicon-containing gas, so that the layer 30 of the layer system shown in FIG. 1 is formed.

In a next process step, the addition of the silicon-containing gas is continuously reduced to zero, so that only the hydrocarbon-containing gas is introduced into the vacuum chamber and the DLC layer 40 of the layer system is formed.

In FIG. 2, the improvement of adhesion is a DLC layer shown when using the method according to the invention against the adhesion of layer systems, which are prepared by a conventional method.

The HF adhesive works specified correspond to those when tested in accordance with the German VDI guideline 3198 , the diagram shown in FIG. 2 also generally showing the qualitative differences. In the case of a smooth surface of a metallic substrate, the adhesive strength of a DLC layer with an adhesion-promoting, silicon-containing layer has a value of about 3.5 in the case of a plasma etching with pure argon, in the case of plasma etching with an argon / H ₂ mixture Value of 4, for plasma etching with an Ar / O ₂ / H ₂ mixture a value of 2.8 and for plasma etching with an Ar / O ₂ mixture a value of about 2.2.

In the case of a rough surface of a metallic substrate, the adhesive strength of a DLC layer with an adhesion-promoting, silicon-containing layer reaches a value of 5 in the case of plasma etching with pure argon and 5.5 in the case of plasma etching with an Ar / H ₂ mixture a value of 3 for plasma etching with an Ar / O ₂ / H ₂ mixture and also a value of 3 for plasma etching with an Ar / O ₂ mixture.

Claims (14)

1. A method for producing a coating of a metallic substrate in a recipient, in which method the substrate is etched on the surface by means of an inert gas in a plasma and then coated using a plasma-assisted CVD method, characterized in that the inert gas contains an oxygen-containing agent at least temporarily Gas is added. 2. The method according to claim 1, characterized in that the oxygen-containing gas accounts for 1% to 80%, preferably from 10% to 50%. 3. The method according to claim 1 or 2, characterized characterized in that the etching in the plasma for a period between 1 min and 60 min, preferably between 5 min and is carried out for 20 minutes. 4. The method according to any one of claims 1 to 3, characterized in that the etching process is carried out under a pressure between 10 ^-4 mbar and 10 mbar. 5. The method according to any one of claims 1 to 4, characterized characterized in that in the CVD process silicon-containing gas is introduced into the vacuum chamber. 6. The method according to claim 5, characterized in that the silicon-containing gas from a silicon-containing Monomer, in particular from silane, tetramethylsilane, Tetraethoxysilane, hexamethyldisiloxane and / or Hexamethyldisilane is formed. 7. The method according to any one of claims 1 to 6, characterized characterized in that in the CVD process hydrocarbon-containing gas, which consists in particular of methane, Ethane, ethene, ethyne, cyclohexane and / or benzene is formed, is introduced into the vacuum chamber. 8. The method according to claim 7, characterized in that the hydrocarbon-containing gas in addition to that silicon-containing gas is added. 9. The method according to claim 1, characterized in that in the CVD process, the silicon-containing gas and then additionally the hydrocarbon-containing gas in the vacuum chamber is introduced and then the feed of the silicon-containing gas is stopped, the Supply of the silicon-containing gas preferably is continuously reduced. 10. The method according to any one of claims 7 to 9, characterized characterized in that the hydrocarbons of the hydrocarbon-containing gas heteroatoms, such as nitrogen, Oxygen, silicon and / or fluorine include. 11. The method according to any one of claims 7 to 10, characterized characterized in that the hydrocarbon-containing gas a gas is added that contains nitrogen, oxygen, Includes silicon and / or fluorine. 12. The method according to any one of claims 1 to 11, characterized in that the CVD process is carried out under a pressure between 10 ^-4 mbar and 1 mbar. 13. The method according to any one of claims 1 to 12, characterized characterized in that in the CVD process diamond-like carbon layer is formed. 14. The method according to any one of claims 1 to 13, characterized characterized in that in the CVD process Multilayer system is formed.