WO2008000573A2 - Wear-resistant coating and production method for the same - Google Patents

Abstract

The invention relates to a wear-resistant coating for a machine part, subjected to frictional wear, comprising a carbon-based hydrogen-containing functional layer (4), with a nanostructure, for example by means of different subsequent layers (60, 61, 62) with nanometre range thicknesses or embedded nanoparticles (63, 64).

Description

 Wear resistant coating and manufacturing process for this

The invention is in the field of tribology and is concerned with the coating of machine parts to reduce friction losses and wear. The present invention is basically applicable to many different types of machine parts that are subject to abrasive wear. However, a particularly advantageous example is the use in parts of internal combustion engines, in particular in valve train components such as tappets used. However, an application for industrial use such as in bearings and linear guides is also conceivable.

Basically, the demands on such components by increasing mechanical loads, movement speeds and service life are getting higher. Increasingly lower maintenance intensity is assumed. Corresponding lubricants are used because of the increasing demands on the environmental compatibility with fewer and fewer additives and the trend is sometimes to low-viscosity lubricants or even to operate without lubricants.

The corresponding requirements for low frictional forces and adhesion both in the liquid-lubricated, dry and transitional areas, low adhesion forces, high wear resistance and, at the same time, toughness and resistance to spalling are no longer met by conventional coatings.

In part, some of the requirements may be met by specific coatings, such as hardness or low frictional resistance, but regularly suffer from other characteristics of the tri-biological system.

This becomes particularly clear with the example of valve trains in internal combustion engines, where particular attention is paid to cam stoppers. is located.

Such cam follower devices are incorporated, for example, in reciprocating piston engine engines having air intake and exhaust valves that open and close in phase with, or in synchronism with, the rotation of the crankshaft. A valve drive mechanism is used to transmit the movement of the camshaft mounted cam to the valves as the camshaft rotates with the crankshaft of the engine. In this case, the cam of the camshaft is in frictional contact with a running surface of the associated tappet.

In general, such valve train components, such as, for example, cup and pump tappets, are subject to increasing demands. The reasons for the need for increased wear resistance lie in the ever-increasing loads and stresses of the tribological system, consisting of control cams and tappets. The causes for this are new engine concepts, such as gasoline and diesel direct injection systems, with constantly increasing injection pressures, an increasing proportion of abrasive particles in the lubricant, lack of oil supply to the friction partners, which results in an increased proportion of mixed friction, and Increasing use of tribologically unfavorable steel cams for cost and mass reduction. An important contribution to the conservation of resources is the reduction of friction losses in the valve train, resulting in fuel savings while increasing the life of the entire valve train. In order to effectively reduce the friction losses, it is necessary to reduce the friction torque over a wide speed range.

It is known to form such tappets for the valve control of an internal combustion engine as a light metal plunger, which body has a tappet body and a seated on the contact surface for the control cam of the valve control steel plate with a hardened surface.

A disadvantage of this approach, however, has turned out to be the fact that such bucket tappets are exposed in operation relatively large temperature fluctuations of -30 ° C at cold start up to about 130 ° C during operation of an internal combustion engine. The problem here is the different thermal expansion of the materials used. Although the steel plate inserted as an insert into a light-metal ram has good wear properties, it tends to detach under corresponding thermal stress. The thermal capacity is therefore limited. Another technical disadvantage is that the space is lost in the form of a relatively wide edge as a functional surface or as a cam contact surface, which is contacted by the control cam of a valve control.

According to the prior art, it is likewise known to provide running surfaces of machine parts exposed to frictional wear with wear protection layers which, depending on the application, preferably consist of electroplated metals or metals and / or metal alloys applied with a thermal spraying process, optionally with additions of hard material.

In this case, however, the fact that thermally sprayed metal layers have a relatively weak strength has been found to be disadvantageous, and it is therefore known to reflow the metal layers after application, for example by plasma jets, laser beams, electron beams or by an arc in order to improve the strength in that the spray materials mix and alloy in a molten state with the base material melted down simultaneously in the surface area. In addition, the thermally sprayed and thus rough coatings must be mechanically reworked to have good trochological properties. In remelting, however, inhomogeneous zones of different composition arise in which both the base material and the layer material can predominate. If the base material content is too high, then the layer wear will be too high, and with a low base material content there will be a risk of macrocracking in the case of different layer combinations, so that such layers can not be used. In such a case Friction stresses can cause undesirable adhesive wear on the layers.

Furthermore, it is known to carbonitrate the tread of the tappet by means of a thermochemical process and / or to nitrocarbuheren. However, it has proved to be disadvantageous that no satisfactory coefficient of friction is achieved and too low a wear resistance arises.

It is also known to coat the tread of the tappet with a manganese phosphate layer or a bonded coating. Again, no satisfactory coefficients of friction and wear resistances are achieved. In addition, such materials pollute the environment unnecessarily. The same applies to galvanic layers, which can also be applied to the running surfaces.

There are also known from the prior art as Beschichtungsmatehalien hard metals and Schnellarbeitstahle (ASP 23), which in addition to an unsatisfactory coefficient of friction and an unsatisfactory wear resistance additionally have a disadvantageous high mass.

In addition, hard, for example by a PVD or a (PA) CVD method, produced layers such as TiN, CrN, (Ti, Al) N, known. A disadvantage of this approach, however, has proved the fact that these layers have a high wear of the counter body result if these layers are not reworked. In the case of post-processing, undefined surface states result due to the reactive surfaces.

From US Pat. No. 5,237,967, carbon-based PVD and (PA) CVD layers with 20 to 60 Atoιm-% hydrogen in the top layer known so-called metal-containing hydrocarbon layers (aC: H: Me) and amorphous hydrocarbon layers (aC: H). However, these layers have a relative low wear and fatigue resistance and are therefore not suitable for highly stressed components in new generations of engines and offer a relatively low reduction in friction during operation.

As already explained above, a reduction in friction in the valve train is a necessary contribution to saving fuel and conserving resources. This goal can be achieved by reducing the field of solid and mixed friction and thus increasing the field of fluid friction with complete separation of materials. This is achieved by optimizing the overall roughness of the tribological system consisting of bucket tappets and camshaft.

In order to obtain the necessary optimal surface structure of the tappet over the entire life, it is necessary to make the surface so that it has a high wear resistance, a low adhesive tendency to the counter body and low reactivity to the environment. Furthermore, the surface may preferably not contain any abrasive particles such as droplets.

The tappets made of iron-carbon alloys, even in the heat-treated state, such as carbonized, nitrocarburized or nitrided, do not achieve the requisite wear resistances and tribologically favorable surface conditions. If, for example, nitride layers are treated mechanically, in particular by (fine) grinding, lapping, polishing, blasting, etc., in addition to the surface structure, the chemical composition and reactivity of the surface are also changed. On the one hand, these changes are subject to a great deal of variation, which means that no consistent quality can be achieved. On the other hand, topographically affine surfaces have less favorable tribological properties and tend to adhere to the counterpart body. Furthermore, residual stresses in the near-surface areas are induced by grinding and polishing processes, which add up to the already existing high residual compressive stresses of the hard material layer. In addition, the induced dislocations and the ruptured droplets lead to defects and micro-cracks, so that the local fatigue strength of the layer is reduced in cup tappets and the adhesive strength is reduced to the potential of chipping during reworking of the layer.

However, if, for example, in the layers deposited by means of an arc process, one omits subsequent polishing, the hard droplets lead to abrasive wear of the counter body or at least to a random polishing of the counter body, which results in unfavorable consequences which are not to be foreseen. In addition, the droplets break during operation from the layer, resulting in a layer damage and free, abrasive particles.

It is also known from DE 102004043550 A1 a constellation in which the wear-resistant coating consists of at least one nanocrystalline functional layer of at least two CrN _x phases for a friction reduction and for increasing the wear resistance of the predetermined surface of the machine part. However, this coating also does not meet all the tribological requirements with regard to friction reduction and wear resistance, especially in the mixed friction region in an ideal manner.

Thus, the object of the present invention is to provide a coating and a production method for such a coating which eliminate the abovementioned disadvantages and in particular reduce the frictional torque over the entire area of use and increase the service life of the coated machine part and of the counterpart body.

According to the invention, this object is achieved by a wear-resistant coating with the features of patent claim 1 and by a method having the features of patent claim 21.

Because the functional layer is based on hydrogen-containing carbon is, and in cross-section areas of different consistency, the extent of which in at least one direction 20 nm, better still 10nm, below, a nanostructured layer is formed, in which the areas of different consistency, that is, for example, from different materials, different modification, can fulfill different tasks with different proportions of material or even with different crystal orientation, which are very difficult to meet by a single substance of homogeneous nature. Due to the nanostructuring, however, the friction partner in the functional layer is confronted with different areas at the same time, for example to reduce the sliding friction and to generate the necessary material hardness.

This is also the case if the functional layer is formed at least partially by layers which are essentially parallel to the surface and which form the regions of different consistency. In this case, due to the small thickness of the layers (<20 nm or even <10 nm), either from the very beginning or after a short operating time and starting abrasion, a hybrid surface is created in which different layers are exposed at different points. The surface of the functional layer thus offers the friction partner different surface areas with different hardness, different friction properties, adhesion tendency and different toughness. By such a nanostructuring is additionally formed by the inhomogeneities, a high crack resistance to chipping and peeling of the layer. It can be achieved by suitable design and arrangement of the layers also increased corrosion resistance or increased or decreased wettability with lubricants. Measurements have shown that by the invention the reduction of friction moments by 30% and hardnesses between 15 and 70 GP can be achieved.

In one such constellation, one or more of the layers are advantageously thinner than 10 nm. The number of layers is typically greater than 2 and may be up to several tens, in particular more than 50 or more than 100, so that the total thickness of the layer is up to 10 May be micrometer. Adjacent layers each have a different consistency in that, for example, at least two adjacent layers each have different of the following three consistencies: amorphous, metal-free, hydrogen-containing carbon, amorphous, metal-containing, hydrogen-containing carbon, amorphous, at least one nonmetal-containing, Hydrogen-containing carbon. In principle, process-adjusted impurities of less than 1% may be contained.

In addition, different types of layers may be provided. The non-metals containing hydrogen-containing carbon, for example, typically has the property to reduce frictional forces and, for example, if fluorine, silicon or oxygen is stored, also the property of favoring a low wettability with lubricants. As a result, a thinner oil film is favored, which brings advantages, in particular in the case of rapid relative movements of the friction partners, that is, for example, in valve trains.

The metal-containing amorphous, hydrogen-containing hydrocarbons typically have the properties of hardness and abrasion resistance.

Adjacent layers may also differ only in that they are doped with different materials or that the extent of doping is different.

By doping the material properties, especially when it is a crystalline phase, significantly changed. Thus, the doping can be used specifically to produce certain mechanical properties, the properties thus produced also depend on the nature and size of the doping atoms. In addition, the nature of the resulting crystalline structure depends on the amount of doping atoms insofar as crystalline transformations take place above a certain degree of doping or mixed phases arise from different modifications. Thus, even adjacent layers that differ only by the type or the extent of doping differ, have completely different mechanical or tribological properties.

In addition, adjacent layers can also differ by the percentage of hydrogen in the amorphous carbon. The hydrogen content in the carbon also strongly influences the fundamental tribological properties. Hydrogen contents below 20%, in particular between 5% and 20%, tend to make the hydrogen-containing amorphous carbon harder and are advantageous for the embodiment according to the invention.

Also, the percentage ratio of sp ³ - and sp ² -hybhdisierten carbon can distinguish two adjacent layers from each other. This concerns the carbon which is present in diamond and graphite modification which, as is known, have different mechanical properties. Accordingly, the thus different adjacent layers also have different tribological properties. It is particularly advantageous if the proportion of sp ^{3 "} hybridized carbon atoms is greater than 50% of the carbon atoms.

It can also be advantageously provided that in at least one layer at least one of the parameters: hydrogen content, proportion of the sp ³ -hybridized C atoms, doping perpendicular to the surface of the coating has a gradient.

It is important, above all, that in practical use on the actual friction surface, different areas with different mechanical properties are available.

Due to the described types and constellations of layers and their thickness and sequence from the friction surface, the qualities of the surface can be permanently adjusted for a wide variety of tribological requirements by the proportion of each exposed at the surface areas with high hardness, high toughness or effective friction Reduction predominates or is less weighted. Thus, by appropriate layering of the areas of different consistency, the invention enables an individual adjustment to customer-specific requirements.

It can also be provided according to the invention that the regions are at least partially formed by nanoparticles. These may for example be formed from one or more of the materials: nitride, boride, carbide, silicide. For example, chromium nitride, titanium nitride, silicon nitride, silicon carbide or titanium carbide are conceivable.

Such nanoparticles can be co-deposited with, for example, in the course of a deposition process together with or before or after the deposition of corresponding hydrogen-containing carbon layers.

For this purpose, the corresponding necessary substances are temporarily brought into the gas phase in the separation device, either by sputtering or other known methods and by the process parameters, the crystallization of the particles is promoted. This results in nanodisperse, self-organized regions, either of different crystallites or crystallites of the same structure with different orientations.

For example, so-called nitride formers such as chromium, titanium and other unstable nitride-forming elements such as copper may be deposited together, wherein, for example, when copper and chromium nitride, the copper content compared to the chromium content may be below 2%. Chromium nitride then forms in a copper matrix as a nanocrystal. A similar result can be achieved with titanium nitride and a very low boron content, it also being possible to use titanium carbide instead of titanium nitride and, in any case, to crystallize the corresponding nitride or carbide in a quasi-amorphous boron matrix.

As a result, the corresponding nanoparticles can either be embedded in an amorphous layer consisting of hydrogen-containing carbon or form a nanoparticle layer between the carbon layers.

It is important that the layer formed is thin or the particles are finely distributed, so that at the surface of the functional layer in each case the exposed areas of the nanoparticles occupy only part of the surface and thus other parts through areas of different consistency with other mechanical or tribological properties be occupied.

In addition to the incorporation of nanoparticles, in addition to the inherent mechanical properties, crack propagation is also effectively inhibited in the resulting functional layer. With a size of the nanoparticles below 20 nm, this is optimally ensured even below 10 nm.

Advantageously, the coating below the functional layer has at least one adhesion-promoting layer which consists of chromium, tungsten or titanium or of borides, carbides or nitrides of the transition metals. Such an adhesion promoter stabilizes the overall structure of the coated machine part with the functional layer and in particular prevents detachment of the functional layer. Suitable materials suitable for the machine parts are conventional readily processable and cost-effective materials (16Mn Cr5, C45, 100 Cr6, 31 Cr Mo V9, 80 Cr2 and so forth). As a friction partner, iron / carbon alloys are conceivable in the sense of lightweight construction for weight saving.

In addition, it is particularly advantageous to provide a support layer below the functional layer of a metal-containing or non-metal-containing, hydrogen-containing carbon layer which contains one or more of the components tungsten, tantalum, chromium, vanadium, hafnium, titanium or nickel on the one hand or silicon, oxygen, fluorine, nitrogen on the other hand contains.

Such a supporting layer has the task of absorbing large mechanical force loads acting on the functional layer, so that no excessive ge deformation of the functional layer occurs, which could lead to the detachment of substrates or destruction of the functional layer by cracking and chipping. The intermediate layer is extremely strong, with neither low frictional resistance nor wear resistance. Therefore, the support layer can be designed specifically so that it has a low compliance or is adjusted in the compliance such that it creates an optimal transition between the functional layer and the actual machine part.

The invention further relates to a method for producing a coating according to claim 1 or one of the following, wherein in a deposition process for applying the areas to the surface, the process parameters are changed at successive times such that the size of the areas formed by deposition in cross section the coating falls below 20 nm. It is particularly advantageous if the size of the regions falls below 10 nm.

For this purpose, at least one of the parameters pressure, temperature, admixture of dopants, hydrogen content, rotational speed of carbon content can be changed abruptly or continuously during the production of the functional layer.

During the deposition process as well as any other steps of the coating, such as heating or plasma etching, a process temperature of 250 ° C. is advantageously not exceeded because the hardening of the base material of the machine part is thus retained and reworking, for example by inductive hardening, does not have to take place.

The deposition takes place in the context of known PVD (physical vapor diposition) and (PA) CVD (plasma assisted chemical vapor diposition) method.

In a PVD process, a starting material, such as graphite, heated so that a jet of high-energy carbon ions from the Imitating graphite and accelerated in the direction of the surface to be coated in a field.

In a (PA) CVD process, a gas mixture is introduced into the process chamber with the aid of a plasma, in which the material parts to be coated are located. The (PA) CVD process is a further development of the CVD process and combines the advantages of the CVO process (unrated process) and the PVD process (low temperatures). In the PACVD process, the layer deposition takes place by chemical reaction from the gas phase at temperatures of less than 200 ° C with a targeted plasma support.

By changing the process parameters such as pressure, temperature and hydrogen content and dopants or the Rotationsgeschwidigkeit of the object to be coated, the structure of the resulting coating is determined. In the case of certain parameter limits, there are also sudden changes in the consistency of the deposited layer, since certain, in particular, crystalline configurations can only be formed up to certain material fractions of individual substances. If these components are not present, then another crystal or another modification or a mixed phase is formed.

Thus, by varying the process parameters at appropriate time intervals, correspondingly small (smaller than 10 nm) regions can be deposited either particle-wise or layer-by-layer.

Finally, the invention also relates to machine parts which are provided with the coating according to the invention, in particular to a valve tappet for a cam-actuatable valve of an internal combustion engine.

The invention is shown below with reference to an embodiment with reference to said valve stem in a drawing and described below. Showing:

Figure 1 is a front view of a friction pair, consisting of Tassenstö- and camshaft for the operation of a valve of an internal combustion engine;

Figure 2 is a perspective view of the tappet of Figure 1;

Figure 3 is a perspective view of a hydraulic support element, which is connected via a rolling bearing component with a finger lever in connection;

Figure 4 is a schematic cross-sectional view of a machine part with wear-resistant coating according to an embodiment of the present invention and

Figure 5 representation of a functional layer.

In the figures of the drawing, like reference characters designate like or functionally identical components, unless otherwise indicated.

FIG. 1 illustrates a friction pairing consisting of a tappet 5 with a cam contact surface 50 and a cup skirt 51 as well as a cam 6. The tappet 5 is shown in greater detail in FIG. 2 in a perspective view. The tappet 5 is generally connected for machine parts in internal combustion engines with the shaft 7 of a valve which opens or closes the valve by moving the cam surface against the cam contact surface 50 of the tappet 5.

In general, modern valve train components, such as, for example, cup and pump tappets, are subject to high requirements with respect to wear resistance and resource conservation, in particular with regard to contact area 50.

In conjunction with FIG. 4, which illustrates a schematic cross-sectional view of a wear-resistant coating for a machine part 1, for example for a bucket tappet 5, according to a preferred embodiment of the present invention, an embodiment of the present invention is explained in more detail below.

The tappet 5 is coated with a wear-resistant coating according to the invention for a reduction of the coefficient of friction and for an increase of the wear resistance in the region of the cam contact surface 50 or, if required, in the region of the cam contact surface 50 and the cup 51. In the case of high deformations of the cup skirt 51 of the tappet 50 in the region of the open side, optionally also a partial coating of the cup 51 can take place.

The area 2 to be coated, i. in the present case the cam contact surface 50 of the tappet 5, is preferably case hardened or carbonized and tempered before coating.

The base body, in the present case, the cam contact surface 50 of the tappet 5, which advantageously consists of a cost-effective steel material, such as 16MnCr5, C45, 100Cr6, 31 CrMoV9, 80Cr2 or the like, is first coated with an adhesion-promoting layer 3 according to the present embodiment. The adhesion-promoting layer 3 may, for example, each consist of a metal-containing carbon, for example a compound of tungsten and carbon, but also of metallic materials (eg Cr, Ti), as well as borides, carbides, nitrides and suicides of the transition metals. An additional support layer above the primer layer may consist of an amorphous carbon containing a metal or non-metal such as W, Ta, Cr, V, Hf, Ti, Ni or Si, O, F, N and hydrogen. The adhesion-promoting and the supporting layer can be used in connection with a heat treatment, for example case-hardening, Carbonitriding, nitrocarburizing, by a thermochemical process, for example nitriding, boriding, by a galvanic process, for example by applying a chromium-containing layer, or by a PVD process, for example, application of Me-C, carbides and nitrides of the transition metals, are formed.

The support layer is intended to increase the fatigue strength of the overall coating, i. plastic deformation, cracking, growth and fractures of the layer system can be prevented. Such fatigue operations can be caused by the load on the cam and the material stress of the bucket tappet 5 induced therefrom as well as by different degrees of hardness, moduli of elasticity, deformability of the individual layers or of the main body and of the wear-resistant coating. In this case, a formation of the layer 3 as a support layer 3 either alone or in combination with a suitable adhesion-promoting layer is preferable.

As shown in FIG. 4, according to the present embodiment, a wear-resistant coating 4 is formed over the backing and / or the primer layer 3.

The functional layer 4 is shown there as schematically constructed from many individual nanosheets, wherein the size ratios are reproduced only schematically and not to scale.

In contrast, in FIG. 5, the functional layer is shown to scale greatly enlarged. In this case, the variants are shown in the left half of the figure, which have different superimposed less than 10 nm thick layers, each consisting of a hydrogen-containing amorphous carbon with different consistency, while on the right side of the figure a variant with additional nanodisperse particles is shown.

The scale is widely spaced because of the small thickness of the nanosheets in the direction perpendicular to the surface. The wavy line at the Surface represents the real surface that self-adjusts due to irregularities in manufacturing or after use. The waviness is in reality not as great as shown but appears exaggerated by the uniaxial magnification of the scale perpendicular to the friction surface. Nevertheless, the effect achieved with the invention can be explained on the basis of this illustration. The individual layers 60, 61, 62 are hatched differently at least in the upper area toward the surface and can therefore be distinguished. It turns out that due to the somewhat (a few nm) irregular structure of the surface, at the latest after a first startup and wear at various points, the lower layers 61, 62 and even layers not individually marked below are revealed. These layers each have different tribological properties, so that the entire surface of the friction partner is a mixture of many different areas with different properties in terms of hardness, elasticity, wear resistance and friction coefficient. This state is maintained even if the wear continues to progress, but this is greatly delayed by the said structure and the resulting wear resistance.

The individual layers differ at least partially in relation to the consistency, that is to say the hydrogen content, the type and amount of added, doped substances or crystal modifications and orientations. At the same time, some or many of the layers are open at the surface.

On the right side of FIG. 5, the variant in which nanoparticles 63, 64 are introduced into the carbon matrix is shown. The corresponding nanoparticles, which may be formed, for example, as borides, carbides or nitrides, form where they come to the surface, so for example in the case of the particles 63, 64 hard and wear-resistant areas and thus also prevent the removal of the surrounding material the carbon matrix. This, in turn, contributes somewhat to a reduction in the coefficient of friction, depending on the composition on the surface, for example. If something is removed from the surface of the functional layer in the course of material wear, new nanoparticles are exposed, which then again perform the stated task of ensuring hardness and wear resistance.

In principle, the nanoparticles can also be concentrated in different layers. This can be offered, for example, in the context of the deposition process by introducing between the deposition of the remaining layers during the PVD or PACVD process certain metal nitrides, borides or carbides which are deposited in mixing ratios which automatically form different phases lead. This then leads to the formation of hard nanoparticles in the relevant layer.

The described invention provides a novel coating which, by selection of the particles and the individual nanolayers, allows adaptation to the present tribological requirements in a very accurate manner, whereby macro-range parameters can be set by the mixture of regions with different surface textures can be achieved with any known homogeneous material. The invention also provides a simple production process for such a functional layer, which does not require any constructive changes compared with the production means used hitherto in PVD and (PA) CVD coating.

The maximum coating temperature is preferably 250 ° C, so that in a coating process, the base material is not tempered.

The coating is preferably formed with a thickness of about 0.5 μm to about 10.0 μm, preferably 2.0 μm. As a result, the dimensions and surface roughness of the base body change to such a small extent that no reworking is necessary. In the following, a further advantageous use of the coating according to the invention is explained in more detail. FIG. 3 illustrates a perspective view of a hydraulic support element 8 which has a piston 9 and a housing 10. The hydraulic support element 8 is coupled to a drag lever 11, wherein the drag lever 1 1 is pivotally mounted via a rolling bearing 12. As can also be seen in FIG. 3, the piston 9 has a contact region 90 between the piston 9 and the drag lever 11. Furthermore, the piston 9 has a contact region 91 between the piston 9 and the housing 10. For a reduction of the wear in the contact region 90 between the piston 9 and the drag lever 1 1, the contact region 90 is likewise provided with a nanostructured functional layer 4 according to the invention.

Furthermore, the contact region 91 between the piston 9 and the housing 10 can also be coated with such a coating 3, 4 depending on the application and manufacturing technology. As a result, the overall service life of the illustrated tribological system is increased, as a result of which a failure of the individual machine parts during operation is reduced and thus overall costs can be saved.

In addition, components of the rolling bearing 12, for example, the rolling elements, the inner and outer rings of the rolling bearing 12, the rolling bearing cages, the axial discs or the like also to increase the wear resistance and friction reduction with the functional layer 4 according to the invention with the interposition of, for example, a support and / or primer layer 3 are coated.

Of course, the layer system described above is also suitable for other structural and functional units, such as valve stems or valve stem supports, supporting and inserting elements, roller bearing components, release bearings, piston pins, bearing bushings, control pistons for, for example, injection nozzles in the engine area, linear guides and other mechanical and tribological devices. highly stressed parts suitable.

It should be noted at this point that the functional layer 4 can also be deposited directly on the main body of the machine part to be coated, without a support layer 3 or adhesion-promoting layer 3 being applied therebetween.

Although the present invention has been described above with reference to preferred embodiments, it is not limited thereto but modifiable in a variety of ways.

LIST OF REFERENCE NUMBERS

1 machine part

2 predetermined area of the machine part

3 support layer / adhesion-promoting layer

4 nanocrystalline functional layer

5 tappets

6 cam

7 valve stem

8 hydraulic support element

9 pistons

10 housing

11 drag lever

12 rolling bearings

50 cam contact surface

51 cup shirt

60.61, 62 layers

63.64 nanoparticles

90 contact area between piston and drag lever

91 Contact area between piston and housing

Claims

claims 1. A wear-resistant coating for a machine part, which is exposed to frictional wear, with an amorphous carbon and water-based functional layer, characterized in that the Functional layer in cross-section regions (60, 61, 62, 63, 64) of different consistency, the extent of which is less than 20 nm in at least one direction. 2. Coating according to claim 1, characterized in that the regions (60, 61, 62, 63, 64) are at least partially formed by layers substantially parallel to the surface. 3. Coating according to claim 2, characterized in that at least at least one of the layers (60, 61, 62) is thinner than 10 nm. 4. Coating according to claim 2 or 3, characterized in that adjacent layers (60, 61, 62) each have different consisten- zen. A coating according to claim 4, characterized in that at least two adjacent layers (60, 61, 62) each have different of the following three consistencies: amorphous metal-free carbon with hydrogen, amorphous metal-containing carbon with hydrogen, amorphous carbon containing a non-metal with hydrogen. 6. Coating according to claim 4 or 5, characterized in that adjacent layers (60, 61, 62) differ by the type and / or extent of doping. 7. Coating according to claim 4, 5 or 6, characterized in that that adjacent layers (60, 61, 62) differ by the percentage of hydrogen. 8. Coating according to claim 4 or one of the following, character- ized in that adjacent layers differ by the ratio of sp ³ - and sp ² -hybridized carbon. 9. Coating according to claim 2 or one of the following, characterized in that in at least one layer (60, 61, 62) at least one of the parameters: hydrogen content, proportion of sp ³ -hybhdisierten C- Atoms, doping, perpendicular to the surface of the coating has a gradient. 10. Coating according to claim 2 or one of the following, character- ized in that a top layer of a hydrogen-containing Carbon layer has a doping with fluorine, oxygen and / or silicon. 11. Coating according to claim 1 or one of the following, characterized in that the regions (63, 64) at least partially through Nanoparticles are formed. 12. Coating according to claim 11, characterized in that the nanoparticles (63, 64) are formed from one or more of the materials: nithd, boride, carbide, silicide. 13. Coating according to claim 11 or 12, characterized in that nanoparticles (63, 64) of the same composition are provided with different crystal orientation. 14. Coating according to claim 11, 12 or 13, characterized in that the nanoparticles (63, 64) are converted into a hydrogen-containing carbon monoxide. Substance layer are embedded. 15. Coating according to claim 13, characterized in that a layer of nanocrystalline material is formed. 16. A coating according to claim 1 or one of the following, characterized in that below the functional layer (4) at least one bonding layer (3), which consists essentially of chromium, tungsten or titanium or borides, carbides nitrides or suicides of the transition metals , is provided. 17. Coating according to claim 1 or one of the following claims, characterized in that below the functional layer (4) a support layer (3) made of a hydrogen-containing, metal-containing or non-metal-containing carbon layer is provided which contains one or more of the components tungsten, tantalum, Chromium, vanadium, haffnium, titanium, nickel on the one hand or silicon, oxygen, fluorine, nitrogen on the other hand. 18. Coating according to claim 1 or one of the following, characterized in that the thickness of the functional layer is between 0.5 and 10 micrometers. 19. A coating according to claim 1 or one of the following, character- ized in that the carbon layer less than 20 atomic percent Contains hydrogen. 20. A method for producing a coating according to one of claims 1 to 19, characterized in that in a Abscheververfah- ren for applying the functional layer on the surface at certain time intervals in each case at least one process parameter is changed such that the size of the formed by deposition U.N- Different ranges in the cross section of the coating 20 nm below. 21. The method according to claim 20, characterized in that the process parameters are controlled such that the size of the different regions falls below 10 nm in the cross section of the coating. 22. The method according to claim 20 or 21, characterized in that at least one of the parameters pressure, temperature, admixture of Dopants, hydrogen content rotational speed during the production of the functional layer is repeatedly changed abruptly. 23. The method according to claim 20 or one of the following, character- ized in that the production of the coating is carried out at temperatures below 250 ° C. 24. Valve tappet for a valve actuatable by a cam of an internal combustion engine with a coating according to one of claims 1 to 19.