WO2008128849A1

WO2008128849A1 - Method for applying a wear-resistant coating

Info

Publication number: WO2008128849A1
Application number: PCT/EP2008/053679
Authority: WO
Inventors: Tim Matthias Hosenfeldt; Yashar Musayev
Original assignee: Schaeffler Kg
Priority date: 2007-04-20
Filing date: 2008-03-27
Publication date: 2008-10-30
Also published as: DE102007018716A1; EP2140039A1

Abstract

The invention relates to the application of a tribological layer on a component, wherein the layer contains at least one upper layer (4) with an amorphous carbon or hydrocarbon. According to the invention, in order to simplify the coating method, a lower layer (13) and an upper layer (4), different from said lower layer (13), are consecutively applied by the use of a direct current (DC) plasma-aided CVD method, optionally with modification of the process parameters, and by the use of different precursors.

Description

Method for applying a wear-resistant coating Description

Field of the invention

The invention is in the field of tribology and deals with a method for coating 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 in industrial applications such as in rolling bearings and linear guides and hydraulic support components 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 requirements for low frictional forces and adhesion in both 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 some cases, some of the requirements may be met by coatings of a specific nature, such as hardness or low friction. However, other properties of the tribological system regularly suffer.

This is particularly evident in the example of valve trains in internal combustion engines, where the focus is particularly on cam follower devices.

Such cam follower devices are incorporated, for example, in reciprocating piston engine engines having air intake and exhaust valves which 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 comes into 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 necessity of increased wear resistance lie in the ever-increasing loads and stresses of the tribological system, consisting of control cams and tappets. The reasons 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 tappet, which has a plunger base body and an inserted at the contact surface for the control cam of the valve control steel plate with a hardened surface.

A disadvantage of this approach, however, has been found to be the fact that such tappets in operation relatively large temperature fluctuations of -30 ⁰ C. are exposed during cold start up to about 130 ⁰ 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 with 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 abrasive wear with wear protection layers which, depending on the application, preferably consist of electroplated metals or of metals and / or metal alloys applied optionally with additions of hard material in a thermal spraying process.

Here, 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 by, for example, plasma jets, laser beams, electron beams, or arc so as to improve the strength the spray materials mix and alloy with the base material melted simultaneously in the surface area. 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, frictional 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 nitrocarburize. 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 Friction coefficient and wear resistance achieved. In addition, such materials pollute the environment unnecessarily. The same applies to galvanic layers, which can also be applied to the treads.

Hard metals and high-speed steels (ASP 23) are known from the state of the art as coating materials, but in addition to an unsatisfactory coefficient of friction and unsatisfactory wear resistance, they additionally have a disadvantageously high mass.

In addition, hard, for example by a PVD or a (PA) CVD method, produced layers, such as TiN, CrN, 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 conditions result due to the reactive surfaces.

As already explained above, a reduction in friction in the valve train is a necessary contribution to saving fuel and conserving resources. This is achieved, among other things, by the lowest possible overall roughness of the tribological system consisting of bucket tappet and camshaft.

In order to obtain the required low roughness of the tappet over the entire life, it is necessary to design 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 carbonitrided, nitrocarburised or nitrided, do not achieve the necessary wear resistance 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 wide variations, 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 compressive stresses of the hard material layer.

In addition, the induced dislocations and the ruptured droplets result in voids and microcracks, thus reducing the local fatigue strength of the layer in cup tappets and decreasing the adhesive strength to potential spalling during post-processing of the layer.

However, if, for example, the layers deposited with an arc process are omitted for subsequent polishing, the hard droplets lead to abrasive wear of the counter-body or at least to random polishing of the counter-body, which results in unfavorable consequences. In addition, the droplets break during operation from the layer, resulting in a layer damage and free, abrasive particles.

DE 102004043550 A1 discloses a constellation in which the wear-resistant coating consists of at least one nanocrystalline functional layer comprising at least two CrN _x phases for reducing friction and for increasing the wear resistance of the predetermined surface of the machine part. However, this coating does not meet all tribological requirements in an ideal way.

DE 102005 029 360 A1 discloses a method for plasma treatment, in particular also for plasma coating of a component under approximately atmospheric pressure, in which a CVD coating can be applied by means of suitable precursors using a high voltage of a few KV.

A method for applying chemically functionalized surfaces to functional elements is known from DE 10 2004 057 155 A1, whereby the plasma-assisted coating with precursors, such as acrylic acid, allylamine, diamino cyclohexane, and the resulting functionalizations of the surface are discussed in particular. Further, the document relates to the plasma polymerization.

DE 10 2005 034 764 A1 relates to a process for plasma polymerization for the production of fluorocarbon polymer layers. There is a low-pressure high-frequency plasma at pressures between 0.03 mbar and 1 mbar applied at frequencies in the MHz range. A device for plasma-assisted carbon deposition is known from DE 10 2004 029 526, whereby a spatially distributed arrangement of base points for an arc is sought by a correspondingly optimized design of ignition devices for the plasma.

US Pat. No. 5,237,967 discloses carbon-based PVD and (PA) CVD layers with 20 to 60 atom% of hydrogen in the top layer, so-called metal-containing hydrocarbon layers (Me-C: H) and amorphous hydrocarbon layers (a-C: H).

From WO 03/064874, a coating of a carbon in a diamond-like structure is known for ball bearings in principle in order to improve the overall friction properties and in particular the dry-running properties. EP 454616 discloses a rolling bearing which is partially coated with a chemically deposited diamond material in order to improve the dry running properties, to increase the load capacity and the service life. From DE 69812389 T2, a coating of sp3 and sp2 hybridized carbon compounds, which contains 5 to 25% silicon, is known for rolling element bearings (cf. JP06341445A).

Thus, the present invention has for its object to provide a method for applying a coating that eliminates the above-mentioned disadvantages, in particular simple and inexpensive to apply and leads to coated components that low friction with a long service life of the respective component and also connect the opposite body. The coating process should be possible at the lowest possible temperatures.

The object is achieved according to the invention with the features of claim 1.

The basic idea is to use a direct current (DC) plasma-assisted CVD coating process, both for an undercoat layer to be applied, which typically contains a carbide, a boride or a nitride of a transition metal, as well as for a layer above it Upper layer containing amorphous carbon and / or hydrocarbons.

In order to explain the advantages of this process, in brief, the already known coating processes are briefly described: There are currently two main thin-film methods used to deposit functional layers on an industrial scale: CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition). The conventional thermal CVD methods allow three-dimensional, uniform coating of substrates with complex geometries while achieving excellent layer adhesion. However, the required substrate temperatures of 900 - 1200 ⁰ C are too high for many applications. On the other hand PVD processes enable coatings at temperatures below 400 ⁰ C. As a result, thermal stresses and thermal distortion are significantly reduced and heat-treatments are unnecessary frequently. A major disadvantage, however, is the difficulty of coating substrates with complex geometries. For example, the components often present in automotive technology can often not be coated at all or can only be coated with a great deal of technical equipment. Furthermore, PVD processes require considerably more expensive vacuum systems.

The Plasma Assisted CVD (PACVD) process developed out of a desire to combine the advantages of both processes. This substrates with complex geometries in three dimensions at temperatures of 400 - 500 ⁰ C are coated with a low technical expenditure vacuum at pressures in the range mbar-.

The known plasma-assisted CVD processes no longer use purely thermal energy to activate the chemical reactions, but instead activate the process by means of a plasma in the reactor. This targeted energy input is realized, for example, by:

Pulsed or unpulsed DC plasmas, either unipolar or bipolar, RF plasmas, low- or high-frequency, microwave plasmas acting directly or indirectly on the surface, as well as laser-induced plasmas or UV excitation.

When using a plasma, this has on the one hand a catalytic effect, on the other hand, the task of energy decoupling. This means that reactions can occur at lower temperatures or even become possible. This technique makes it possible to lower the substrate temperature below 500 ^° C. The different types of plasma realization lead to different plasmas. Thus, the RF plasma is a space charge, whereas in the DC plasma the glowing edge lies close to the contour of the cathodic substrate and thus has advantages for coating complex geometries. Therefore, when a DC plasma is used, a component to be coated does not necessarily need to be moved, in particular rotated, in order to achieve a uniform surface coating.

Since the type, composition and structure of the applied layers can be determined using suitable precursors and with appropriate adjustment of process parameters, such as pressure, substrate temperature, plasma voltage, pulsation and frequency of the plasma, the method is suitable for applying various successive layers Layers with the same process, in the same coating chamber and with the same device.

In principle, therefore, different layers such as the underlayer according to the invention and the upper layer can also be produced with the same precursors.

The halogen-containing precursors conventionally used in CVD processes, ie starting materials which are introduced into the plasma and form the basis for the substances introduced into the coating, generate halogens or halogen compounds during the process, which more or less depend on the experimental parameters the layers are incorporated. These halogen corporations can cause undesirable effects. In the deposition of TiN layers by means of TiCl ₄ as a metal dispenser, for example, a low process temperature leads to increasing chlorine incorporation and higher wear of the coatings. The use of steels with low tempering temperatures and light metals in automotive engine construction requires due to the low wear resistance and high friction of the materials used a tailor-made coating of the component surfaces at the lowest possible temperatures, particularly advantageous below 180 ⁰ C. As sub-layers while carbides, nitrides or borides of About - serve transition metals, such as hard Ti (C, N) layers. These can be prepared from organometallic precursors at temperatures below 160 ⁰ C partially.

Organometallic compounds can be used particularly advantageously because of the lower binding energy of the metal-carbon or metal-heteroatom-carbon bond at low temperatures as a precursor in the PACVD process. These molecules have a high reactivity, so that low substrate temperatures are sufficient for the formation of a CVD layer. As precursor should According to an advantageous embodiment of the invention tetrakis (diorganylamino) titanium compounds (eg (Ti (NR ₂ ) ₄ , R = Me, Et, CH ₃ , CH ₂ CH ₃ )) or titanium (IV) - serve isopropyl.

The carbon or hydrocarbon layers can also be deposited from these or similar precursors (eg methane). It should be noted that the coating of a substrate exclusively with a carbon or hydrocarbon layer in the pulsed DC plasma method with an organometallic precursor is conceivable. Amorphous hydrocarbon layers are characterized by a low coefficient of friction, in particular against steel, high hardness and wear resistance, and a high chemical inertness. Typical fields of application are tribological systems in mechanical engineering, such as plain bearings, rolling bearings, shafts, axles, gears, guides and forming tools.

Hydrocarbon layers can be differentiated by their chemical composition into pure amorphous hydrocarbon layers (DLC, a-C: H), modified amorphous hydrocarbon layers (a-C: H: X), and metal-containing amorphous hydrocarbon layers (a-C: H: Me). In this group, the DLC layers have the highest hardnesses (> 20 GPa), the best wear resistance and the highest chemical inertness.

The amorphous or metal-containing amorphous hydrocarbon layers (DLC, Me-C: H) are generally prepared according to the prior art in the HF-PACVD or PVD process. According to the invention, however, the respective layers are to be produced in the DC-PACV D method, in particular unipolar or bipolar pulsed. The advantage lies in the continuous process control of the coating, since the deposition can be carried out inexpensively in the same plant as the deposition of the sublayers. This eliminates the need for an adapter for H F-P AC V D processes. The coating process can be carried out with reduced effort in a much shorter time than before. If tetrakis (diorganylamino) titanium compounds are used as precursors for the preparation of the carbon layers, although CC or CH top layers are formed on the Ti (C; N) layers, low-friction, harder DLC or aC: H: Me upper layers are deposited at temperatures <180 ⁰ C by means of CH ₄ or tetramethylsilane as precursors. Therefore, the topsheet or, if the topsheet is not the topsheet, a topsheet disposed above the topsheet can be applied using CH ₄ or tetramethylsilane as precursors.

In addition, under the cover layer, also using the DC plasma-assisted CVD method, a silicon-containing hydrocarbon layer can be applied as a bonding agent to compensate for the mechanical stresses.

The individual layers in the process described in sub advantageously be strattemperaturen below 180 ⁰ C, particularly advantageously applied even below 160 ⁰ C.

This is supported by the pulsed operation of the DC plasma. In this case, pulse ratios of pulse duration to pulse interval between 0.01 and 15 can be selected depending on the desired or permissible energy input. The DC plasma can be pulsed unipolar or bipolar.

Advantageous voltages of the plasma are between 450 and 650 volts, advantageous frequency range is below 50 kHz, preferably between 20 and 50 kHz.

A further advantageous method step lies in a plasma treatment preceding the coating, in particular plasma cleaning of the surface of the substrate. A major focus is on the environmental compatibility of the pretreatment, since many previously used methods must be replaced due to their pollution.

The invention relates not only to the described method for producing a coating but also to the coating obtained and to machine parts which have been coated by the method according to the invention, in particular to a valve tappet for a cam-actuated valve of an internal combustion engine and to a roller bearing.

In the following the invention with reference to an exemplary embodiment with respect to said valve stem and a hydraulic support member is shown in a drawing and described below.

Showing: Figure 1 is a front view of a friction pair consisting of tappets 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 roller bearing with a cam follower in connection; and

Figure 4 in cross section a layer sequence on a base body / substrate.

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

Fig. 1 shows a friction pairing with a tappet 5 with a cam contact surface 50 and a cup shirt 51 and a cam 6. The tappet 5 is shown below in more 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, not shown, which opens or closes the valve by moving the cam surface against the cam contact surface 50 of the tappet 5.

As is known, valve train components of the automotive industry, such as, for example, cup and pump tappets, are subject to high requirements with respect to wear resistance and resource conservation, in particular at the contact surface 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 cup tappet 5, according to a preferred embodiment of the present invention, an implementation of the present invention is explained in more detail below.

The tappet 5 is provided with a wear-resistant and low-friction coating according to the invention for reducing the coefficient of friction and for increasing 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 Trap high deformations of the cup 51 of the tappet 50 in the open side, can optionally also be a partial coating of the cup 51 done.

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

The main body 1, in the present case, the tappet 5, which advantageously consists of a cost-effective steel material, such as 16MnCr5, C45, 100O6, 31 CrMoV9, 80Cr2 or the like, is first coated with an underlayer 13 according to the present embodiment. This may consist of a carbide, a nitride or boride of a transition metal, preferably of TiN or TiC and be applied in a pulsed DC-PACVD method using a tetrakis (diorganylamino) titanium compound as a precursor. Thereafter, an adhesion-promoting layer 3 can optionally be applied to the underlayer. The adhesion-promoting layer 3 can consist, for example, of a metal-containing carbon or hydrocarbon, for example in each case in conjunction with tungsten, but preferably of a silicon-containing hydrocarbon.

The underlayer 13 is intended to increase the fatigue strength of the overall coating, i. it should be 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, formation of the layer 13 as a subbing layer, either alone or in combination with a suitable primer layer 3, is preferable.

As shown in FIG. 4, according to the present embodiment, a wear-resistant layer 4 is formed over the undercoat and / or the adhesion promoting layer 3 as a top or top layer.

The layer 4 is shown there schematically, wherein the size ratios are not reproduced to scale.

The functional layer or upper layer 4, which may also be identical to the cover layer, is characterized by a carbon-containing layer, a hydrocarbon-containing layer Layer, a modified or a metal-containing amorphous hydrocarbon layer is formed, in which the carbon is present in sp2 and sp3 hybridized form and the sp3 bonds are advantageously more than 50%.

If the carbon-containing CC and CN top layers obtained directly from the organometallic precursors TMT and TET (Ti (NR ₂ →, R = Me; Et) are unsuitable for the respective purpose due to their properties, then an alternative subsequent deposition of DLC or aC: H: Me upper layers at temperatures <180 ^° C. from hydrocarbons or silanes provided in the multilayer method, which can be supported by too high residual stresses by a likewise deposited aC: H: Si adhesion promoter layer 3.

The environmentally friendly pre-treatment is being given increasing attention today, as many previous processes have to be replaced due to their high environmental impact. Before the coating process, the substrates are therefore advantageously subjected to a solvent-free ultrasound treatment and in addition to a plasma cleaning. The plasma cleaning takes place in the form of a "sputter cleaning" with variation of plasma voltage and gas mixture in the same device as the subsequent coating.

The described invention provides a novel coating process which requires only manageable structural changes with respect to the necessary coating device compared with the previously used production means in PVD and (PA) CVD coating.

The maximum coating temperature is preferably from 180 ⁰ C, so that the base material is not annealed at a coating operation.

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 1 1, 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 frictional contact region 90 the drag lever 1 1 on. Furthermore, the piston 9 has a frictional contact region 91 between the lateral surface of 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 coating 13, 4 according to the invention, optionally with a bonding agent layer 3.

Furthermore, the contact region 91 between the piston 9 and the housing 10 can also be coated with such a coating 13, 4. As a result, the overall service life of the illustrated tribological system is increased, whereby a failure of the individual machine parts can be reduced during operation and thus a total cost 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 can also be provided to increase the wear resistance and to reduce friction with the coating of the invention.

The layer system described above is of course also for other construction and functional units, such as valve stems or valve stem supports, support and plug-in elements, rolling bearing components, release bearing, piston pin, bushings, control piston for example injectors in the engine area, linear guides and other mechanical and tribologically highly stressed parts suitable. In order to adapt the coating process to the respective desired properties of the coating and to emphasize the diversity of the different partial layers, the following parameters are adapted and controlled during coating:

Substrate temperature (T) Coating time (t)

Heating, cooling rate of the substrate during the coating

Gas mixture (N ₂ , H ₂ , Ar, TMT, TET, CH ₄ , TMS)

Process gas pressure (p) in the recipient

Gas flow (m) voltage (U)

Pulse / pause ratio (PD / PP) of the plasma

Ratio of additional heating / plasma power Successful tests for the coating of metallic substrates by means of an organometallic precursor were carried out with the following process parameters:

Coating temperature: 160-180 ^° C. Pressure: 50-300 Pa

Gas flow: 20 - 60 l / h

Plasma parameters Voltage U: 450 - 650 V Bipolar pulsed 20 - 5O kHz

Duty cycle PD / PP: 0.01 - 15

(PD: pulse duration, PP: pulse pause)

Precursor / evaporator temperature: Ti (NMe ₂ ) ₄ : 35-55 ⁰ C Ti (NEt ₂ ) ₄ : 75-100 ⁰ C CH ₄ TMS 35 ⁰ C

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 component, basic body

2 to be coated surface 3 adhesion promoting layer

4 upper class

5 tappets

6 cam

7 valve stem 8 hydraulic support element

9 pistons

10 housing

1 1 drag lever

12 rolling bearings 13 lower layer

50 cam contact surface

51 cup shirt

90 contact area between piston and drag lever

91 Contact area between piston and housing

Claims

claims

1. A method for applying an underlayer (13), consisting of a Car bid, a nitride or boride of a transition metal, in particular Ti N, Ti C, and an overlying upper layer (4), the amorphous carbon or

Hydrocarbon contains, on a metallic base body (1), characterized in that first applied by applying a direct current (DC) plasma-assisted CV D method, the lower layer (13) and then using the same method, the upper layer (4) auf- is brought.

2. The method according to claim 1, characterized in that the application of the lower layer (13) and the upper layer (4) in the same coating chamber is performed with the same coating device.

3. The method according to claim 1 or 2, characterized in that the application of the lower layer (13) and the upper layer (4) is carried out using the same precursor.

4. The method according to claim 1 or one of the following, characterized in that when applying the lower layer (13) is used as precursor an organometallic compound.

5. The method according to claim 4, characterized in that as precursor titanium (IV) isopropylate or a tetrakis (Diorganylamino) titanium compound is used.

6. The method of claim 1, 2, 4 or 5, characterized in that the upper layer (4) or arranged on the upper layer layer using hydrocarbons or silanes as precursors in the DC

Plasma-assisted CVD method is applied.

7. The method according to claim 6, characterized in that immediately below the cover layer or the upper layer, a silicon-containing amorphous hydrocarbon layer (3) as a primer in the DC plasma-assisted

CVD method is applied.

8. The method according to claim 1 or one of the following, characterized in that the application of the lower layer (13), the upper layer (4) and optionally the cover layer is carried out at substrate temperatures below 180 ° C.

9. The method according to claim 1 or one of the following, characterized in that the DC plasma-assisted CVD method is performed with pulsed DC plasma.

10. The method according to claim 9, characterized in that the DC plasma is bipolar pulsed.

1 1. A method according to claim 10, characterized in that the DC plasma is pulsed at a voltage between 450 and 650 volts.

12. The method according to claim 10, characterized in that the DC plasma is pulsed at a frequency between 20 and 50 kHz.

13. The method of claim 10, 11 or 12, characterized in that the duty cycle of pulse duration to pulse interval is between 0.01 and 15.

14. The method according to claim 1 or one of the following, characterized in that the metallic base body (1) is cleaned before applying the lower layer (13) using the DC plasma.

15. Component with a surface exposed to mechanical wear, characterized in that a tribological coating is produced according to one of claims 1 to 14.

16. cup tappet (5) which is designed to be longitudinally displaceable for actuation by a camshaft at its bottom, characterized in that a tribological coating in the region of interaction with the camshaft, produced according to one of claims 1 to 14.

17. Rolling bearing (12) with a tribological coating in the region of the raceways on the inner and / or outer ring or on the surface of the rolling elements, produced according to one of claims 1 to 14.