DE102009008271A1 - Method for coating a substrate with a carbon-containing hard material by depositing in the gas phase comprises post-treating the deposited hard material layer for controlled adjustment of friction with a hydrogen and/or oxygen plasma - Google Patents

Abstract

Method for coating a substrate with a carbon-containing hard material by depositing in the gas phase comprises post-treating the deposited hard material layer for controlled adjustment of friction with a hydrogen and/or oxygen plasma.

Description

The The invention relates to a method according to the preamble of Claim 1.

Such a method is z. B. off DE 10 2007 047 629 A1 known. In this case, a substrate, for example a workpiece, with a hard amorphous carbon layer, a so-called diamond-like carbon or DLC layer by plasma enhanced chemical vapor deposition (PECVD) in a reaction chamber from a gas phase an inert shielding gas a hydrocarbon such as methane in a vacuum of 10 ^-2 mbar or less deposited. The DLC coating provides the workpiece with high wear protection and generally significantly reduces the coefficient of friction. The disadvantage, however, is that the coefficient of friction is subject to considerable fluctuations depending on the termination of the surface.

task It is therefore the object of the invention to use carbon-containing hard material layers provide a controlled reduced, so pre-defined low Have friction coefficients.

This is inventively achieved in that the deposited hard material layer of a subsequent treatment with a hydrogen and / or oxygen plasma is subjected.

Thereby According to the invention, carbon-containing hard material layers with a controlled reduced, so a consistent obtained low coefficient of friction.

The Fluctuations in the coefficient of friction of the deposited carbonaceous Namely, hard material layers of the prior art are likely to related to the fact that the hard material layer according to their Deposition free bonds, so-called "dangling bonds" has. If after deposition of the hard material layer on the substrate the The evacuated reaction chamber is flooded with nitrogen is of it assume that due to the inertness of nitrogen only one negligible proportion of free bonds in the near-surface region the layer is passivated. Once the reaction chamber is open is, therefore, it comes to an uncontrolled passivation of a Most of the remaining free bonds, through the oxygen of the air, but also by hydrogen, for example from the humidity. Similar events occur during Flooding with atmospheric air. For hydrocarbons, For example, methane, as a reaction gas are also in the layer contained hydrogen atoms to passivate the free bonds to the near-surface area of the layer available posed. The share of these processes in the definition of the surface termination varies, for example, with the environmental conditions and is a priori unknown.

By the aftertreatment of the deposited according to the invention Hard material layer with hydrogen and / or oxygen plasma is a defined termination of the amorphous carbon, so a Saturation of free bonds in the near-surface Layer reached.

The Substrate may be made of metal, ceramic, plastic or the like. It can be a workpiece or a material. To the adhesion too improve, an adhesive layer can be applied to the substrate, before the hard material layer is deposited. For a substrate made of steel, the adhesive layer, for example, titanium, chromium or the like, being applied by sputtering can.

Of the Carbon-containing hard material may be a carbide, for example tungsten, Titanium or silicon carbide be. Preferably, however, a hard material layer made of amorphous, undoped carbon, so a DLC layer, the Subjected after treatment according to the invention. The layer thickness of the carbon-containing hard material layer can be, for example 0.1 μm to 50 μm, in particular 0.5 μm to 10 microns.

The hard amorphous carbon or DLC has sp ³ -hybridized bonds. A high proportion of sp ³ -hybridized bonds is present in particular with tetrahedral amorphous carbon. In addition to the tretrahedral amorphous carbon, the hard amorphous carbon or DLC layer may also consist of amorphous, hydrogen-saturated carbon.

to Coating the substrate with the hard amorphous carbon or DLC layer can be the chemical vapor deposition or "Chemical Vapor deposition (CVD) or physical vapor deposition (PVD). The CVD method is included preferably carried out as a "plasma enhanced" or PECVD method. This is a coating of amorphous, hydrogen-saturated Carbon formed.

In this case, a commercially available PECVD system can be used. The deposition of the amorphous, hydrogen-saturated carbon layer can be carried out at a pressure of less than 10 ^-2 mbar. The temperature in the deposition chamber is preferably more than 100 ° C, in particular 200 to 250 ° C. The reaction gas supplied to the deposition chamber consists of a Hydrocarbon, in particular methane and / or acetylene, which is supplied together with an inert gas, for example argon, the deposition chamber.

For the deposition of the tetrahedral amorphous carbon, in particular the vacuum arc discharge has proven to be suitable. In this case, a DC vacuum arc is generated, wherein the cathode (target) consists of graphite, which is sublimated by the arc. In order to control the sublimation, an inert gas, such as argon, is used as the background gas. The process pressure is preferably less than 10 ^-2 mbar. The chamber wall serves as an anode. The arc burns in the steam generated by it.

The Vacuum arc discharge is preferably carried out super-pulsed, d. H. the DC voltage is superimposed on an AC voltage. there can a DC power source of z. B. 60 to 800 A and a pulse source from, for example, 20 to 30 A are used. The high currents of z. B. 30 seconds duration are preferably by shutdown from Z. B. 90 seconds, so that the temperature of the coated substrate not too high, so preferably does not exceed 150 ° C. During the pauses in the pulse receives the direct current the arc discharge upright.

The layer of tetrahedral amorphous carbon obtained by vacuum arc discharge is then preferably graphitized under pressure and, for example, smoothed by brushing, whereby the layer thickness is reduced (see EP 1 829 986 A1 ).

To the deposition of the carbon-containing hard material, ie in particular DLC layer is the deposition chamber z. B. flooded with nitrogen.

The Hydrogen and / or oxygen plasma with which the carbonaceous Hard material, ie in particular DLC layer is aftertreated to a controlled low friction coefficient is obtained preferably generated with a microwave plasma system. The hydrogen and / or oxygen plasma is heated by the microwave, the generated by a magnetron and in the evacuated reaction chamber is coupled.

There in a pure microwave plasma very high powers needed can be, the carbonaceous hard material, ie in particular However, the DLC layer erodes and thereby increased Friction coefficient can be obtained.

Preferably Therefore, an electron cyclotron resonance or ECR plasma system for Post-treatment of the carbon-containing hard material or DLC layer used. With such a system are microwaves, for example with a frequency of 2.45 GHz, produced by a magnetron be, for example via a waveguide and a window z. B. coupled from ceramic into the reaction chamber. With a Magnetic field, which is generated by magnetic coils, there is a gyration of Electrons of the plasma, thereby increasing the path of the electrons lengthened and thus the number of shocks is increased. In this way, more energy can enter the plasma be coupled. Thus, a high plasma density becomes lower Ion energy generated.

The Hydrogen and oxygen ions of the plasma meet with less Energy on the hard material or DLC layer so that they in the Layer preferably only a maximum of 10 nm, in particular a maximum of 2 nm penetration. A change in roughness is not detectable. The surface is rendered hydrogen by this ion bombardment. or oxygen-terminated.

An ECR plasma system is described in more detail in publications and reports of the Institute of Plasma Physics of the Max Planck Society (cf. Bernhard Landkammer, Investigation of the erosion of hydrocarbon layers by oxygen-gas discharges, Max Planck Institute for Plasma Physics, 1999 ).

The Friction between two solids is composed of several Components, namely solid-state mechanical interactions (Hertzian theory, mechanical interlocking), hydrodynamic Forces and adhesion (in particular Van der Waals Forces) together, the hydrodynamic forces depends on the intermediate medium between the tribo partners are and especially at low load and high relative Affect speeds.

By the aftertreatment according to the invention of the carbonaceous Hard material or DLC layer are in particular the hydrodynamic and the adhesive portion of the friction controls, ie reproducibly reduced.

By the post-treatment with the hydrogen plasma become the surface the deposited carbonaceous hard or DLC layer more hydrophobic Characteristics, which in hydrophilic intermediate media to a Reduction of hydrodynamic friction lead.

In order to obtain a certain low coefficient of friction, however, the low friction value achieved after the hydrotreating can be set to a certain higher value in which the hydrogen plasma treatment is followed by an oxygen plasma treatment.

at certain intermediate media may also possibly only an oxygen plasma treatment be carried out, without prior hydrogen plasma treatment.

The The following examples serve for further explanation the invention.

Example 1:

Two steel discs, each provided with a sputtered chromium adhesive layer approximately 100 nm thick, are coated with a ca. 2 μm thick tetrahedral amorphous carbon layer by super-pulsed vacuum arc discharge with a graphite target under the following process conditions:
Process pressure 5 × 10 ^-5 mbar, direct current source 60 to 80 A, pulse source 20 to 30 A, current pulses of 30 seconds with cooling phases of 90 seconds, temperature less than 150 ° C.

After deposition of the DLC layer, the coating chamber is flooded with nitrogen. The layered slices are then smoothed and then post-treated in an ECR plasma system with a hydrogen plasma under the following process conditions:
Microwave power 70 W, frequency 2.54 GHz, duration 900 seconds, 7 × 10 ^-6 mbar, hydrogen pressure 0.5 Pa.

Example 2:

One of the two discs, which have been subjected to a hydrogen plasma treatment according to Example 1, is then subjected to an oxygen plasma treatment in the ECR plasma system under the following process conditions:
Microwave power 300 W, frequency 2.45 GHz, duration 5 minutes, base pressure 7 × 10 ^-6 mbar, oxygen pressure 0.56 Pa.

The Coefficient of friction of the treated according to Examples 1 and 2 after DLC coatings were made with a tribometer from Optiomal Instruments by vibratory fretting (SRV) measurement determined with a steel ball with a diameter of 1 cm.

To one drop of deionized water was added to the slices given with a volume of about 0.1 ml. Then the steel ball became on the drops of water on the slices at a temperature of 30 ° C with a force of 20, 50 and 100 N pressed and reciprocated at a frequency of 20 Hz.

The results obtained are in the attached diagram whose coordinate represents the coefficient of friction μ, and the abscissa the time in minutes.

The curve ( 1 ) is the measured coefficient of friction of the DLC layer treated with the hydrogen plasma according to Example 1 (only), and the curve ( 2 ) The coefficient of friction of the after Example 2, first with the hydrogen plasma and then treated with the oxygen plasma DLC layer.

It It can be seen that at a low load of 20 N, the coefficient of friction the only with the hydrogen plasma treated DLC layer essential and that is about 30% less than the coefficient of friction of subsequently treated with the oxygen plasma DLC layer. At higher loads of 50 or 100 N, this difference lower, which is due to the fact that by hydrogen plasma treatment (without oxygen plasma treatment) in particular, the hydrodynamic portion of the friction significantly reduced has been.

With the method of the invention can For example, a gear transmission and the camshaft, ram, Pistons, piston rings, cylinder surfaces and / or valves made of motors wear-resistant and low-friction become. However, the invention is also in numerous other fields can be used, for example in medicine for coating artificial Joints.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102007047629 A1 [0002]
• - EP 1829986 A1 [0015]

Cited non-patent literature

• - Bernhard Landkammer, Investigation of the erosion of hydrocarbon layers by oxygen-gas discharges, Max Planck Institute for Plasma Physics, 1999 [0021]

Claims (7)

Method for coating a substrate with a carbon-containing hard material by deposition from the gas phase, characterized in that the deposited hard material layer for controlled adjustment of the friction of a post-treatment with a hydrogen and / or oxygen plasma is subjected. Method according to claim 1, characterized in that that the deposited hard material layer by amorphous carbon is formed. Method according to claim 1 or 2, characterized that the deposition from the gas phase by chemical or physical Gas phase deposition takes place. Method according to Claims 2 and 3, characterized that the physical vapor deposition by vacuum arc discharge is performed with a cathode of graphite. Method according to claim 1, characterized in that that the hydrogen and / or oxygen plasma for the treatment of Hard material layer is produced with a microwave plasma system. Method according to claim 5, characterized in that that as a microwave plasma system, an electron cyclotron resonance plasma system is used. Method according to claim 1, characterized in that that the hard material layer first a hydrogen plasma and then an oxygen plasma treatment is subjected.