EP3129519A1

EP3129519A1 - Tribological system with reduced counter body wear

Info

Publication number: EP3129519A1
Application number: EP15716018.5A
Authority: EP
Inventors: Juergen Ramm; Florian Seibert; Benno Widrig
Original assignee: Oerlikon Surface Solutions AG Pfaeffikon
Current assignee: Oerlikon Surface Solutions AG Pfaeffikon
Priority date: 2014-04-09
Filing date: 2015-04-09
Publication date: 2017-02-15
Also published as: JP2017514017A; US20170211174A1; KR20160145084A; CN106460158A; WO2015155275A1

Abstract

The invention relates to a tribological system with a substantially improved tribological behavior, said system at least partly covering a body with a first contact surface by means of a first coating and a counter body with a second contact surface by means of a second coating and comprising lubricant as an intermediate agent. The invention is characterized in that the first and the second coating each has a layer as the outermost layer. The composition of the outermost layer of the first coating and the composition of the outermost layer of the second coating are selected such that • both outermost layers lubricate steel surfaces upon being exposed to steel so as to make tribological contact, and • both outermost layers are materially related layers such that the element composition of the first outermost layer and the element composition of the second outermost layer match by at least 60 at.%.

Description

Tribological system with reduced counter body wear

The present invention relates to a tribological system with significantly improved tribological behavior and reduced Gegenkörperverschleiss according to claim 1.

The optimization of tribological behavior is an essential goal in the design of tools and components used in machinery, internal combustion engines and transmissions. In many cases, the one partner (hereinafter referred to as "tribological body" or simply as "body") of the tribological system is provided with a layer. With this coating, one pursues different goals, above all, it is intended to reduce the wear of the body, for example with a cutting tool. This is especially true for tooling applications, but is also important for components. Often, in tribological systems in which two components are in tribological contact, not only is the wear of a partner, i. In addition, the wear of the other partner in tribological contact (hereinafter referred to as "counter-body") can be reduced In many component applications, eg in the engine area, the friction coefficient in the tribological system is ultimately reduced, which is usually a prerequisite This is because wear on the tribocontact (tribocontact = tribological contact) is reduced.The use of coatings for such applications has been proven for decades and both tool coatings and component coatings are widely used.

Coatings of tools and components are often made by Physical Vapor Deposition (PVD) or Plasma Enhanced Chemical Vapor Deposition (PECVD) technology. The prior art includes coating methods such as sputtering, cathodic Funkenen evaporation and plasma-assisted CVD or combinations of these methods. The method of cathodic sputtering is mainly used in the field of tool coating in cutting, punching and forming tools. It is also used to a limited extent for component coating, for example, for coating piston rings with chromium nitride (CrN). This coating process is robust and reliable and allows you to synthesize a wide range of coating materials. The disadvantage of this method are splashes that occur during the evaporation process of the cathode material and are partially incorporated into the coatings as so-called droplets. This increases their surface roughness and makes it necessary for these layers to be post-treated for applications where low coefficients of friction are necessary. In the case of applications of CrN layers on piston rings, the usual layer thickness is between 30 μm and 50 μm. About 3 to 5um are removed by the post-treatment, so that the necessary for the layer surface Surface roughness is achieved. If one does not carry out this aftertreatment, on the one hand there is the danger that the top coarseness of the CrN layer (characterized by the Rpk and Rpkx values) causes the counterpart body to become very worn and, in addition, breakouts of splashes or layer particles can occur. because they have a higher hardness than the counter body, they additionally cause a quicker erosion due to the "emery effect." However, the after-treatment steps mentioned for smoothing the applied layers are standard procedures and long-established in the mass production and should not deal with a specific type of aftertreatment but the term is intended to encompass all types of surface roughness enhancements such as polishing, lapping, brushing, grinding, etc.

problem

Of course, it would be advantageous to be able to dispense with a post-treatment, which is possible in the current state of the art only for selected coating methods and only a few carbon-based materials. However, not all problems are solved with the aftertreatment and improvement of the layer surface. In many cases, the coated body, as is the case for example with the piston rings, occasionally operated for a short time in lack of lubrication. An important requirement of such tribological systems is therefore that they do not completely fail even in the case of insufficient lubrication, i. that neither destruction of the layer nor destruction of the counter body occurs. Since the layer material is usually chosen to be harder in its mechanical properties than the counter-body material, there is a risk that counter-body material is transferred to the layer material or lubricated in deficient lubrication. For the investigation of such tribological systems, in which the behavior of body and counter-body is examined, the vibration s-rubbing-wear test (SRV test, English, "reciprocating wear test") was developed. On the basis of this test, the problem of lubricating will now be clarified and the inventive results will be explained. All measurements in the SRV test were made with the same parameters regarding frequency, glide path, test force and test temperature, i. that all test results are comparable.

For the tests, bodies were coated with different materials by the method of reactive cathodic sparks evaporation. As a body polished discs (022mm x 5.6mm) made of steel (90MnCrV8, 1.2842) were used, the one Rockwell hardness> 62HRC and possessed a surface roughness Ra≤ 0.05pm. Polished steel balls made of 100Cr6 (hardened steel, 60 - 68 HRC, 0 10mm) were used as counterparts. The mechanical properties of the layer materials to be compared were determined by the nanoindentation method and are summarized in Table 1. It will be understood by those skilled in the art that these changes may also be made by changes in the coating process, and they are only mentioned herein to indicate typical magnitude relationships and to better understand the results of the SRV tests. The SRV tests were performed on CrN, molybdenum nitride (MoN) and molybdenum-copper-nitride (MoCuN) for different conditions:

A. Dry [A1] (i.e., without lubricant, such as oil) or lubricated [A2] (always use a diesel oil as lubricant in the experiments carried out here)

B. Coated Body + Uncoated Counter Body [B1] or Coated Body + Coated Counter Body [B2]

C. With after-treatment of the coating [C1] or without aftertreatment of the coating [C2]

Table 1: Mechanical properties of the layers used for the SRV tests

1. SRV test: dry, coated body and uncoated counter body, without post-treatment of the layer

Figure 1 shows the friction coefficients obtained in the SRV test for the CrN, MoN and MoCuN coated bodies obtained in contact with the polished steel ball without using a lubricant and without post-treatment. The coefficient of friction of CrN (1) lies in the range between 0.7 and 0.8, making it the largest among the investigated layers. MoCuN (3) initially shows a coefficient of friction of 0.7, but after a short time it drops to 0.6 and below. This curve is characterized by high noise. MoN (2) starts with the smallest friction coefficient of 0.5, which at the end of the test approaches that of the MoCuN, which lies in the range between 0.5 and 0.6. As the curve progresses, there are some "breakouts" that can be explained by short-term greasing of the counter-body material, but each time it seems to be Relieve lubrication again. The greater "noise" in the curve of the MoCuN, which occurs after about 10 minutes, is attributed to the fact that this layer has a higher number of, above all, larger splashes, which is due to the fact that the MoCu targets, which serve as the cathode for When compared to the pure Mo targets, the sparks are usually more likely to spatter, and these spatters are partially reflected in the deposited layer.

Figure 2 shows the photographs taken with the light microscope after the SRV test, which characterize the wear marks on the layers (a-c) and the associated wear on the counter-bodies (d-f). The top line of the table illustrates the wear of the layers in the rubbing track. It turns out that the CrN (a) (also detected by an EDX analysis) comes to smear the counterbody material (100Cr6) on the layer surface, while such smearing MoN (b) and MoCuN (c) layers is not detectable , The wear of the counter body is shown in the bottom line of Figure 2. The diameter of the wear cap, the part of the uncoated counter body that was abraded in the SRV test, is the largest in the case of the CrN coated body (d). For MoN (e) one finds the least wear. In this case, there is a partial transfer from the Mo-containing layer material to the counter body (darkening of the wear cap). MoCuN (f) takes a mean position with respect to wear, but also shows the Mo and Cu containing carry on the counter body. This greasing of the counter body seems to be a major reason why there is no transfer of material to the layer.

In summary, it can be said that unlike the CrN coatings, the MoN layers do not cause greasing of the counter-body material on the layer even though the layers were not post-treated and no lubricant was used. The reason for this is that the counter body is at least partially lubricated by a Mo-containing layer. If one compares with the CrN, one can conclude that the lubrication of the counter body for its wear reduction of greater importance than an adaptation to its hardness. An adaptation of the layer hardness is used, for example, in the case of CrN, by reducing it for steel counter-bodies, which can be achieved by changing the coating parameters. The lower layer hardness leads to less wear of the counter body in lack lubrication, of course, on the other hand, the risk of higher Schichtversch leisses.

It should also be noted that some carbonaceous layers sacrificing part of their own layered material also contain the graphitic carbon counterpart can smear. At high surface pressures, however, these layer systems fail, which is probably due to the fact that the lubrication of the counter body does not have good adhesion and also the "sacrifice" of the layer at higher temperatures can not be controlled and happens too fast.Also depends the reliability of this carbon lubrication in lubricated contact strongly from the lubricant.

For the sake of completeness and without the results being specified here in detail, it should be noted that even the aftertreatment of the layer under these dry test conditions brings no significant improvement, neither for the reduction of the layer wear nor for the Gegenkörperverschleisses. A polishing of the layer defuses this problem somewhat, by the run-in behavior with smaller coefficients of friction takes place, but it does not solve, because usually after a brief frictional contact, the greasing of the mating body material begins again on the layer, especially if the layer material does not lubricate the counter body ,

2. SRV test: smeared, coated body and uncoated counter body, without post-treatment of the layer

In further experiments lubricated conditions were examined for the above case. The tests were carried out with coated body without post-treatment and uncoated polished counter-body. The lubricant used was a standard diesel oil. Experiments were also carried out with other oils that gave qualitatively the same results, although, for example, the coefficients of friction were significantly lower for a 0W20 Mo DTC oil than for diesel oil. The coefficients of friction determined with the diesel oil are shown in Figure 3. They are much smaller under lubricated conditions and are all in a narrow band between about 0.15 and 0.2. While the coefficient of friction of CrN after running in is more or less stable, one can notice a slight steady decrease in the coefficients of friction for MoN and MoCuN. The associated wear images are summarized in Figure 4. Wear on the layers can hardly be determined. It essentially comes to a smoothing of the layer. Presumably, individual splashes, which are not carried away by forced lubricant transport under these simplified test conditions, result in minimal scratch marks in the coating. On the other hand, the wear of the uncoated counter body is clearly visible. For MoN, the wear cap diameter is the largest in this test, which may be due to the fact that this material also has the greatest hardness. There is no significant difference between CrN and MoCuN. In summary, it can be said that the additional lubricant contributes to a strong reduction of the friction coefficient and the layer wear compared to dry test conditions and that in all cases no material transfer of the counter body comes to the layer, as was observed for CrN under dry conditions. Although the counter body wear is lower compared to the dry conditions, it remains prominent and is greatest for the hardest of the layers, namely MoN.

3. SRV test: comparative investigations on MoN coatings

First, the results for the MoN coating that results for the lubricated case, the coated body with aftertreatment of the coating, and the uncoated polished counter body are shown. These are conditions that are used today in the prior art for tribological systems and lead to good results. They should therefore serve as a bar in order to be able to better assess the subsequent inventive step. For these conditions, using the diesel oil as a lubricant, the friction coefficient curve (1) shown in Figure 5 is obtained, which finally stabilizes at values around 0.2. It should be mentioned again here that the coefficient of friction is very clearly dependent on the respective lubricant and, for example, for otherwise identical test conditions, for a 0W20 Mo-DTC-oil under the same conditions is 0.07. In addition, two more temporal curves of the friction coefficient in Figure 5 were shown. The curve (2) shows the course for dry conditions, for the coated body with aftertreatment and the uncoated polished counter-body. The coefficient of friction at the end of the test is between 0.5 and 0.6 across much of the curve, so it is not very different from the one obtained without post-treatment of the layer (see Figure 1). Towards the end of the curve, however, it suddenly rises and then drops off again. Short-term greasing of the mating body material could be the cause. In addition, in the figure, the course of the coefficient of friction was recorded, which for dry conditions, coated body and coated counter-body, but on both sides not after treated layer resulted (3). Surprisingly, this curve usually runs below (2) and ends well below this curve. The wear on the MoN layers and their counterparts is shown in Figure 6. For (1) no wear of the layer can be detected. Also with the counter body it comes to no wear. The markings of the layer and the counter-body are created by the decoration of the lubricant and the diameter in the decoration of the counter-body arises only through its elastic deformation in the body Hertzian contact This result is typical of a tribological contact as it is desired and is the aim of optimizing a tribological contact by means of coatings, curve (2) shows little wear of the layer (coloring is again a decoration by the oil). However, the counter body has a significant wear, which hardly differs from the case A1 / B1 / C2 in Figure 1. For the curve (3), the time course of the friction coefficient shows an interesting behavior. Comparing (1) with (3) in Figure 5, the course of the latter shows, after a certain time, a steady decrease in the coefficient of friction between 0.5 and 0.8 to a value of approximately 0.4. This effect could be explained as a kind of self-smoothing. The friction coefficient of 0.4 is still too large for most applications. But the reference to a self-smoothing effect with similar, non-treated coatings of body and counter-body was surprising.

For this reason, experiments were carried out in which both the body and the counter body were coated with the same layer material. After coating, neither the coated body nor the coated counterpart body was aftertreated. Figure 7 shows the measured friction coefficients as a function of time. The CrN system runs with the lowest friction coefficient of 0.4 and rises to values between 0.4 and 0.5 during the test. MoCuN starts at a friction coefficient of 0.5 and falls after a few minutes about the value of CrN. The coefficient of friction of MoN (this curve has already been shown in Figure 5) as the hardest layer initially has values between 0.5 and 0.6, and at the end of the test also falls to values between 0.4 and 0.5. Table 5 shows the corresponding wear images. Compared with an uncoated and polished counter body (Figure 2), the coating of the counter body leads in all cases to a significantly smaller diameter of the wear cap, thus, therefore, to a lower counter body wear. There is little difference between CrN and MoN in this respect. Even with MoCuN, the wear cap diameter is only marginally larger. Noticeable here are the increased deposits at the edges of the wear track, which is due to the larger splash density that occurs in the cathodic arc evaporation of MoCu. At the end of the test, the coefficients of friction are close to each other. Greasing does not take place under these conditions.

The results so far can be summarized as follows:

• In dry running (applies analogously, albeit less so to deficient lubrication), the uncoated 100Cr6 counter-body is worn with or without after-treatment of the layer. In many layer systems (here only CrN shown as an example, but valid for almost all Al-containing layers such as AICrN, AlCrO, TiAIN but also for many hard nitride layers such as TiN, ZrN, NbN) in the case of a softer counter body material transfer from the counter body to the harder layer .

Although the MoN-based layers also wear the counter body under these conditions, there is no material transfer from the counter body to the layer. The reason for this is that the MoN-based layers smear the counterbody with a Mo-containing layer,

• Without a post-treatment of the layer, the uncoated counter body is worn even under lubricated conditions, although the friction coefficient is small,

• A coating not only of the body but also of the counter body, significantly reduces both the friction coefficient of the tribological system and the wear of the counter body for dry conditions. The effect of greasing is omitted.

From the described, the following problems to be solved can be derived:

• Many tribological systems where only the body is coated (e.g., CrN) will fail, even if they are in the area of insufficient lubrication or dry friction for a short time. Possible causes may be an insufficient or briefly interrupted lubricant supply or a short-term high contact pressure of the friction partners, which pushed away the lubricant from the contact surface more than expected. As a result, and because the layer material usually has the better mechanical and thermal properties, one observes a greasing of the counter body on the coated body. The greasing of the counter-body material can lead to seizure in the tribological system and to partial or total blockage. Therefore, the feeding must be prevented. The most important object of the invention is therefore to avoid or reduce the wear of the counter body in contact with a coated body, if the tribological system runs into a deficient lubrication.

• Layers that are produced by means of cathodic spark evaporation (but also other PVD layers such as those produced by sputtering) and which must meet the requirements for tribological applications generally have to be aftertreated in order to reduce their surface roughness and thus their counter-body wear. The aftertreatment requires depending on Substrate geometry great effort and also an optimal after-treatment should be matched to the counter-body (eg surface quality). Therefore, it is a further object of the invention that post-treatment of the coated parts intended for use under lubricated conditions is no longer necessary.

• There is usually no free choice of a counter body material mechanically adapted to the layer in order to optimize a tribological system. Reasons for this are high material costs, availability of such a material or because the processing of such a material is too difficult and expensive. This limitation is to be remedied.

Description of the inventive solution

The described problem is solved by a coating not only of the body, but in addition of the counter body, wherein the coatings of the body and the counter body have substantially the same material related layers on their surface.

The layers are selected in such a way that the essentially related coatings of body and counter-body smooth themselves with the addition of a lubricant, without the need for aftertreatment even for one of the layers.

Material-related layers in the context of the present invention are layers that have an elemental composition that is not necessarily the same but that is at least 80 atomic percent.

That is, a first layer or a first coating and a second layer or coating are material related layers or related coatings if the elemental composition of the first layer or coating matches the elemental composition of the second layer or coating at least 60 atomic percent.

Another condition for solving the problem is the property of the layer material to lubricate the counter body at least partially.

Another condition for solving the problem is the property of the layer material that the existing in the layer or its surface splashes (also called Droplets) are not intimately connected to the layer, ie can be easily removed, demonstrable by about a post-treatment and determination of the Surface finish, wherein after the post-treatment Rpk and Rpkx are smaller than Rvk and Rvkx.

The solution is based on a coating containing Mo or MoN consisting of a MoN-based layer material that may contain additional dopants of other elements.

The coating of body and counter-body is carried out by means of a PVD method or a PECVD method or a combination of these methods. The preferred method for the coating is reactive cathodic sputtering. In this method, the cathode (= target) of Mo or an alloy of Mo and one or more corresponding doping element (s) is vaporized by cathodic sparks in vacuo and the corresponding reactive gas is evaporated Process added via a gas flow regulator. Either the reactive gas addition is controlled by the gas flow or by the total pressure. The process is well known to those skilled in the art and has been used for industrial scale coatings for many years. Of course, the dopants can also be introduced via a further target from the doping material or else into the coating for the addition of gases. In the latter case, the gas is supplied to the spark discharge or another gas discharge via a controllable gas inlet and correspondingly decomposed or excited wholly or partly in the plasma of the spark discharge or another auxiliary plasma. In this way, for example, MoN or MoCuN (ie MoN layers with Cu doping) can be produced. Characteristic of layers that are produced by means of spark evaporation, the roughness of the layer surface, which is mainly due to macroparticles {or splashes), which arise in the sparks evaporation, but which can also occur in an evaporation by sputtering, for example. However, the increase in roughness in / on the layer by these spatters is striking, especially in cathodic sputtering. A post-treatment, for example, by polishing or

Brushing or microblasting does not cause a significant reduction in roughness in all layers made by cathodic sputtering. This is due to the fact that the incorporation of the splashes in the layer takes place with different levels of stability and that, for this reason, the layers can be treated more or less well. In the case of the MoN-based layer, however, the aftertreatment works well, both for the pure MoN layers and for the layers with dopants. This is shown in Figure 9, in which the roughness of MoN layers of about the same thickness as that of MoCuN before and after the aftertreatment (here, for example, by brushing, but this is not to be understood as a limitation on this method) is compared. The original roughness of the polished steel substrate was Rz = 0.2 μm and Ra = 0.02 μm. This means that the coating significantly increases the original roughness of the uncoated, polished substrate. Depending on the type of coating, this increase in roughness can be different, as shown by the values in the figure for a MoN (black) and a MoCuN (gray) layer. In the figure, two layers are compared, which have approximately the same layer thickness of 2 pm. However, experience also shows that the layer roughness in the spark coating not only depends on the coating material but also increases with the layer thickness, since the number of splashes striking the substrate surface accumulate. Aftertreatment of the layers should therefore either remove the splashes from the layer surface or they should be smoothed easily. The data in Figure 9 shows that this is true for the MoN and MoCuN layers. In the figure, the roughness parameters of the layers before the aftertreatment are indicated in the left quadrant, and those of the aftertreated ones in the right quadrant. The comparison shows, on the one hand, that the after-treatment has a clear effect. This can be seen in addition to the significant reduction of the Rz and Ra values, especially at the peak roughness Rpk and Rpkx. It is also surprising that the post-treated MoN and MoCuN layers hardly differ in the roughness values. That was significantly different before the aftertreatment. The Rz and Ra values for MoN and MoCuN differed markedly, with MoCuN having values approximately twice as large as MoN. The differences in the Rpk and Rpkx values before the aftertreatment were even clearer, disappearing only slightly after the aftertreatment. The Rvk and Rvkx values also show a significant reduction after the aftertreatment, but the difference between the two layers remains more pronounced than is the case for the other roughness parameters.

The investigations in Figure 9 were performed on substrates that had a well-polished substrate surface before coating. It is obvious that in many applications no such well-polished surfaces are present and these often can not be produced or only with great economic effort. Therefore, "technical surfaces" whose roughness values are in the range of layer roughness or even higher were also measured in Table 6. Typical surfaces of valve stems before and after coating were measured in Table 6. The Rpkx value on the stem of the valves was 1.33 pm The valve stem was brushed and then a roughness measurement was performed again, reducing the Rpkx value to about 25% of the original value, which means that the original roughness of the valve stem surface was significantly reduced by the combination of coating and aftertreatment. This is astonishing also from the point of view, since the mechanical properties, for example of the MoN layer, have significantly higher values in terms of hardness and modulus of elasticity (see Table 1) than is the case for both cold work steel and high speed steel. An explanation can not be given for that.

Table 2: Comparison of surface parameters before and after MoN coating (with post-treatment) of valve stems

In summary, it can be said that the MoN-based layers can be easily post-treated and there is a significant reduction in the characteristic of the peak roughness Rpk and Rpkx. In addition, it is possible to reduce the original substrate roughness by a combination of coating and post-treatment.

Now that the preparation and the properties of the MoN-based layers have been described with regard to their aftertreatment capability, the invention will be discussed in more detail, which could be related to these properties in a manner not yet clarified. Referring to Figure 7 and Figure 8, it has already been found that the SRV test, in the event that both the body and the counterbody are coated, provides reasonably astonishing results under dry conditions in the SRV test:

• The coefficient of friction was significantly lower for MoN (0.4 to 0.5) compared to the case of the coated body with after-treatment and the uncoated polished counterbody (0.5 to 0.6) • The counter body wear was significantly lower compared to the case of the coated body without aftertreatment and the polished uncoated counter body for lubricated conditions.

It also shows that a low coefficient of friction is not a sufficient condition for a low Gegenkörperverschieiss, friction coefficient and Gegenkörperverschieiss must necessarily for a tribological, especially the latter shows the complex behavior of Gegenkörperverschteisses friction coefficient, surface roughness of the partners in the tribological contact and the hardnesses of the two friction partners System to be optimized.

4. SRV test: Lubricated, coated body and coated counter body, without post-treatment of the layers

Based on the results discussed above, it has now been of great interest to perform the SRV coated body and coated counter-body test under lubricated conditions. The curves of the coefficient of friction for these tests are shown in Figure 10. All curves show very low noise, which can only be compared with that of curve 1 in Figure 3. The highest coefficient of friction of about 0.2 is found in the CrN coated mating. MoN and MoCuN can hardly be distinguished from each other. This even applies to the run-in behavior. At the end of the test, the coefficient of friction shows values between 0.16 and 0.17. These coefficients of friction are thus no greater than that of the curve 2 in Figure 3, which is 0.17. From the above investigations, however, it was learned that a low coefficient of friction does not guarantee a low wear, especially not with respect to the counter body failure. The wear tests are given in Table 2. There is virtually no wear on the layers. Only in the case of CrN can one recognize streaks which indicate both the decoration by the lubricating oil and scratches by the chips carved out of the layer. The counter body also has such stripes on CrN. Noteworthy is the fact that in spite of the greater surface roughness of the MoCuN no such streaks occur in the corresponding counterbody. Both MoN and MoCuN can not measure wear, neither on the layers nor on the counterpart. Only a two-sided smoothing is observed whose range is determined by the deformation due to the Hertzian pressure. These results show that when the body and the counter body are coated and lubricated in MoN-based material, self-smoothing occurs, ie neither of the two coatings must be treated to achieve such ideal conditions as shown in curve 1 of Figure 5.

The present invention is an excellent solution for improving the tribological behavior and reducing the wear of:

Splitting of worm gears, planetary gears, differential gears, crank gears, roller gears, gearboxes, screw drives, crank gears, locking gears such as gears, spur gears. Ball wheels and their axles and bearings

Parts of compressors such as pistons, vanes, blades, rotary valves

Parts of ball bearings such as balls, cages, rollers, rollers

Sharing pumps such as push pins, plungers, pistons

Tools such as injection molding tools, forming and punching tools, thread cutting tools, cutting tools

Parts of machine tools such as clamping systems, fittings, guide rails

Parts of textile machines such as thread guides, spindles, spinning rings, twine holders

Parts of internal combustion engines and their propulsion systems, such as cylinders, pistons, piston pins, plungers, key plungers, pestles, flat plungers, mushroom plungers, roller plungers, pistons, piston rings, piston pump, connecting rod, connecting rod bearings, radial shaft seals, bearings, bushes, crankshaft shafts, crankshaft bearings, camshafts, camshaft bearings, Gear drive, crank rod, oil pump, water pump injection system, rocker arm, rocker arm, tow lift], body, turbocharger parts, vanes, bolts, valve timing, valvetrain, intake and exhaust valves, bearings of coolant pumps, parts of injection pumps

Clockworks and their components

Parts of vacuum pumps such as forepumps, roots pumps and

Turbomolecular pumps, in particular bearings

Seals and valves

Sharing turbines like bearings and rods

Sharing wind generators such as bearings Captions of the pictures:

• Figure 1: Time course of the friction coefficients under the SRV test conditions A1 / B1 / C2 for the coatings of the body with CrN (1), MoN (2) and MoCuN (3).

• Figure 2: Photomicrographs of the wear track on the CrN (a), MoN (b) and MoCuN (c) layer (top line) with the corresponding wear of the uncoated counter body (df, bottom line) for the test conditions A1 / B1 / C2 ,

• Figure 3; Time course of the friction coefficients under the SRV test conditions A2 / B1 / C2 for the coatings of the body with CrN (1), MoN (2) and MoCuN (3).

• Figure 4; Optical micrographs of the wear track on the CrN (a), MoN (b) and MoCuN (c) layer (top line) with the corresponding wear of the uncoated counterbody (d-f, bottom line) for the test conditions A2 / B1 / C2.

• Figure 5: Time course of the coefficients of friction in the case of MoN coatings for the test conditions A2 / B1 / C1 (1), A1 / B1 / C1 (2) and A1 / B2 / C2.

• Figure 6: Comparison of the wear for MoN layers for different conditions in the SRV test, light microscopy of the wear track (top line) and the corresponding wear of the counter body (bottom line) for the conditions A2 / B1 / C1 (a vs d), A1 / B1 / C1 (b vs e) and A1 / B2 / C2 (c vs f),

• Figure 7: Time course of the friction coefficients under the SRV test conditions A1 / B2 / C2 for the coatings of the body with CrN (1), MoN (2) and MoCuN (3),

Figure 8: Photomicrographs of the wear track on the CrN (a), MoN (b) and MoCuN (c) layer (top line) with the corresponding wear of the same layer coated counter body (df, bottom line) for the test conditions A1 / B2 / C2.

• Figure 9: Comparison of MoN and MoCuN layers before (left) and after (right) after-treatment. It can be seen that the aftertreatment leads to a significant reduction of the Rpk and Rpkx values. This is also true for the Rvk and Rvkx values. But the reduction of these values is less pronounced than with the Rpk and Rpkx values (for definition of the values see [2]).

• Figure 10: Time course of the friction coefficients under the SRV test conditions A2 / B2 / C2 for the coatings of the body with CrN (1), MoN (2) and MoCuN (3). Figure 11: Photomicrographs of the wear track on the CrN (a), MoN (b) and MoCuN (c) layer (upper line) with the corresponding wear of the uncoated counter body (df, bottom line) for the test conditions A2 / B2 / C2.

Specifically, the invention relates to a triboiogical system comprising a body having a first contact surface at least partially coated with a first coating, a counter body having a second contact surface at least partially coated with a second coating and lubricant as an intermediate means, characterized in that the first and the second coating each having a layer as the outermost layer, wherein the composition of the outermost layer of the first coating and the composition of the outermost layer of the second coating are selected, wherein

• Both outermost layers lubricate steel surfaces when exposed to steel under tribological contact, and

Both the outermost layers are material-related layers, so that the elemental composition of the first outermost layer coincides with the elemental composition of the second outermost layer at least in 60 atomic percent.

According to a preferred embodiment of the present invention, the surface of the outermost layer of the first coating and / or the surface of the outermost layer of the second coating is not aftertreated such that the surface of the outermost layer of the first coating and / or the surface of the outermost layer of the second Coating at the beginning of the tribological contact (between the contact surfaces of the body and the counter body) Droplets have, which can be smoothed and / or removed by the relative movement of the coated contact surfaces. Such outermost layers with droplets can be deposited, for example, by means of arc vaporization. Are layers generally have excellent film quality, but at the same time have the disadvantage of having droplets. Therefore, such layers must be aftertreated before tribological application such that the droplets are smoothed or removed. However, the droplets according to this preferred embodiment of the present invention are not detrimental but, on the contrary, are very advantageous because these droplets contribute to the mutual smoothing without producing layer damage or layer flaking. In tribological systems according to the present invention, in particular, the inventors observed very good tribological behavior when the droplets were not intimately bonded to the layers. The inventors have further found that in these cases, the roughness values Rpk and Rpkx of the examined exposed layers after mechanical post-treatment or after tribological contact during operation of the tribological system were smaller than the roughness values Rvk and Rvkx.

According to a further preferred embodiment, the outermost layer of the first coating and / or the outermost layer of the second coating contains molybdenum. Even more preferably, the outermost layer of the first coating and / or the outermost layer of the second coating contain molybdenum nitride.

The inventors have also found it to be very advantageous that at least one of the molybdenum nitride-containing layers contains a doping element or a combination of doping elements composed of the elements Cu, Cr, Ti, Zr. Si, O, C, Zr, Nb, Ag, Hf, Ta, W, B, Y, Pt, Au, Pd and V. Preferably, at least in one of the molybdenum nitride-containing layers, the doping element is Cu or the combination of doping elements contains mostly Cu.

According to yet another preferred embodiment of the present invention, the first and / or the second coating has at least one further layer below the outer layer, wherein the lower layer is an oxide layer. This embodiment is particularly advantageous when the tribological system is first operated at a low temperature, for example room temperature, and subsequently operated at higher temperatures. In these cases, it may also be that the oxide layers are deposited by means of are-evaporation. The exposed layers may then function as sacrificial layers to initiate the saturation of the coated contact surfaces. In this way, the droplets of the oxide layers are gently smoothed or removed without causing the droplets in the oxide layers to damage or flake the coatings. Preferably, the first and second coatings each have an oxide layer below the outermost layer, wherein the coalescence of the two oxide layers is selected such that the oxide layers are material-related layers, such that the composition of the oxide layer in the first coating coincides with the composition of the oxide layer the second coating is at least 60 atomic percent.

Preferably, at least the outermost layers of the coatings are deposited by means of arc evaporation. In this way, at least the droplets present in the outermost layers are "characteristic droplets produced by means of arc vaporization" and the layers have an excellent layer quality with regard to further layer properties.

Preferably, the oxide layers are deposited by means of Are evaporation and therefore have "characteristic Droplets" and excellent layer quality.

However, the first and the second coating may also have further lower layers, which may be, for example, one or more support layers, or one or more adhesion layers to increase the adhesion between the coating and the substrate.

Claims

Expectations

1. Tribological system, which comprises a body with a first contact surface at least partially coated with a first coating, a counter body with a second contact surface at least partially coated with a second coating and lubricant as an intermediate, characterized in that the first and the second coating respectively have a layer as the outermost layer, the composition of the outermost layer of the first coating and the composition of the outermost layer of the second coating being selected such that

• Lubricate both outermost layers of steel surfaces when exposed to tribological contact with steel, and

• Both outermost layers are material-related layers, so that the elemental composition of the first outermost layer matches the elemental composition of the second outermost layer at least in 60 atomic percent.

2, tribological system according to claim 1, characterized in that the surface of the outermost layer of the first coating and / or the surface of the outermost layer of the second coating at the beginning of the tribological contact between the contact surfaces of the body and counter body have droplets, which are through the Allow the relative movement of the coated contact surfaces to be smoothed and/or removed.

3. Tribological system according to claim 2, characterized in that the droplets are not intimately connected to the layers, so that the roughness values Rpk and Rpkx after mechanical aftertreatment or after tribological contact during operation of the tribological system are smaller than the roughness values Rvk and Rvkx are.

4. Tribological system according to one of the preceding claims, characterized in that the outermost layer of the first coating and / or the outermost layer of the second coating contains molybdenum.

5. Tribological system according to one of the preceding claims, characterized in that the outermost layer of the first coating and / or the outermost layer of the second coating contains molybdenum nitride,

6. Tribological system according to claim 5, characterized in that at least one of the molybdenum nitride-containing layers has a doping element or a combination of doping elements made up of the elements Cu, Cr, Ti, Zr, Si, O, C, Zr, Nb, Ag, Hf , Ta, W, B, Y, Pt, Au, Pd and V.

7. Tribological system according to claim 6, characterized in that at least in one of the molybdenum nitride-containing layers the doping element is Cu or the combination of doping elements largely contains Cu.

8. Tribological system according to one of the preceding claims, characterized in that the first and / or the second coating has at least one further layer under the outer layer, the lower layer being an oxide layer.

9. Tribological system according to claim 8, characterized in that both the first and the second coating have an oxide layer under the outermost layer, the composition of the two oxide layers being selected so that the oxide layers are material-related layers, so that the composition of the Oxide layer in the first coating matches the composition of the oxide layer in the second coating at least in 60 atomic percent.

10. Tribological system according to one of claims 2 to 9, characterized in that at least the outermost layers of the coatings were deposited by means of Are evaporation and therefore the droplets present are characteristic droplets which were produced during the implementation of the Are evaporation process.

11. Tribological system according to one of claims 8 to 10, characterized in that the oxide layers were deposited by means of arc evaporation and therefore have characteristic droplets.