AT517721A4 - Method for producing a sliding bearing element - Google Patents

Abstract

The invention relates to a method for producing a sliding bearing element (1) according to which a composite material of a first layer and one or more further layer (s) is produced, wherein the further layer or one of the further layers is formed as a sliding layer (9), and as a sliding layer (9), a casting alloy of a lead-free copper-based alloy is produced, wherein in the copper-based alloy precipitates (10) are introduced, which have at least one alloying constituent of the copper-based alloy. The copper-base alloy is thermochemically treated after solidification, wherein the copper-base alloy is contacted with at least one oxidizing agent, and the oxidizing agent is diffused into the copper-base alloy so that at least one alloying constituent of the copper-base alloy is at least partially oxidized to form the precipitates (10) within the copper-base alloy wherein the precipitates (10) are formed only within a sub-layer (12) of the copper-base alloy.

Description

The invention relates to a method for producing a sliding bearing element according to which a composite material of a first layer and one or more further layer (s) is produced, wherein the further layer or one of the further layers is formed as a sliding layer, and as a sliding layer of a casting alloy of a lead-free copper-base alloy is prepared, wherein in the copper-based alloy precipitates are introduced, which have at least one alloying constituent of the copper-based alloy. Further, the invention relates to a sliding bearing member made of a composite material comprising a supporting metal layer and a sliding layer and optionally an intermediate layer between the supporting metal layer and the sliding layer, wherein the sliding layer is formed of a casting alloy of a lead-free copper-base alloy, in the precipitates having at least one alloying constituent of the copper-based alloy , are included.

Lead bronzes have long been used in slide bearings for the engine industry because they have a good-natured tribological behavior through the lead precipitates. In addition, their casting technology production is very robust from the process engineering point of view, since the metallurgical phenomena of micro segregation and the associated voids formation are prevented or compensated by the lead. For environmental reasons, however, leaded bronzes should be avoided. There are already various approaches of sliding layer alloys in the prior art. For example, in cast alloys based on brass or bronzes, with the aid of alloying additions, e.g. Chromium, manganese, zirconium or aluminum tries to improve the friction properties and in particular to reduce the tendency to eat. However, so far neither the tribological behavior nor the stability of the casting of

Lead bronzes for a sliding layer of a plain bearing are satisfactorily replicated with lead-free bronzes. This leads to problems with lead-free bronze alloys, since defects form during solidification. In addition, the directional solidification forms a microstructure which exhibits an increased tendency to crack in the case of tensile stresses in one direction.

It is the object of the invention to provide a plain bearing having a copper-based lead-free cast alloy as a sliding layer, the copper-base alloy exhibiting at least a similar tribological behavior as lead-containing bronzes.

This object is achieved with the aforementioned method for producing a sliding bearing element, after which the copper-based alloy is thermochemically treated after solidification, wherein the copper-based alloy is brought into contact with at least one oxidizing agent, and the oxidizing agent is diffused into the copper-base alloy, so that at least one alloying component of Copper-based alloy is at least partially oxidized to form precipitates within the copper-base alloy, wherein the precipitates are formed only within a sub-layer of the copper-base alloy. The object is further achieved with the slide bearing element mentioned above, in which the precipitates are formed only within a partial layer of the copper-base alloy.

Due to the precipitates formed, the hardness of the sub-layer decreases compared to the hardness of the starting material, whereby the sub-layer, which is close to the surface of the sliding layer, has a reduced tendency to seize. Obviously, the precipitates themselves act at least partially as solid lubricant, and can therefore replace the lead of lead-containing bronzes. Nevertheless, they prevent crack propagation, as a result of which the microstructure in the partial layer of the sliding layer becomes more viscous. In the preferred embodiment of the method, according to which the production of the precipitates takes place only after the casting of the alloy, moreover, the casting itself can be improved since the alloy system can be made simpler without precipitation particles added in advance. In addition, possibly occurring defects in the

Casting be used in the surface of the casting alloy to improve the process, since smaller pores favor the diffusion of the oxidizing agent in the alloy, so that the process time can be shortened. Despite the imperfections, however, it does not occur due to the particles to pronounced cracking.

However, it should be mentioned at this point that a faultless casting is primarily preferred.

Preferably, the oxidation is carried out with an oxidizing agent selected from a group consisting of or consisting of oxygen and oxygen donating compounds. Especially with oxygen or oxygen donating compounds as the oxidizing agent, the process time can be shortened because oxygen is more rapidly diffused due to the small molecule.

It may further be provided that thermomechanical treatment of the solidified copper-base alloy is performed before or simultaneously with the thermochemical treatment, whereby the toughness of the copper-base alloy can be improved. In addition, it can be achieved that for the production of the final form of the sliding layer does not need to be heated again after the thermochemical treatment, if the deformation takes place at elevated temperature, whereby the risk of changes in the mechanical properties of the copper-based alloy, for example by Rekristallisationserscheinungen reduced can be. Furthermore, a change in the precipitates due to thermo-mechanical processing of the sliding layer subsequent to the thermochemical treatment can thus be at least largely avoided. However, it is also advantageous that the structure of the copper-based alloy can be made more diffusible by the thermomechanical treatment by the formation of more grain boundaries, whereby the thermochemical treatment can be improved.

Preferably, a copper-based alloy is used, which comprises one or more of the elements from a group comprising boron, antimony, aluminum, silicon, vanadium, phosphorus, titanium, manganese, tin, zinc, magnesium. In particular, these elements, i. their oxides, compared to copper oxides on a much more negative free enthalpy, whereby the process flow can be simplified insofar as the risk of oxidation of copper during the thermochemical treatment of the copper-based alloy can be significantly reduced.

The thermochemical treatment of the copper-base alloy may be performed prior to the composite formation with the support metal layer. This has the advantage that with the composite formation, for example by roll cladding, possibly existing defects are at least partially cured. In addition, the layer thickness of the sub-layer can be reduced, whereby the proportion of precipitates per unit volume in the sub-layer can be increased. As a result, the duration of the oxidation process can be reduced, since it can be terminated as desired even with a lower proportion of precipitates per unit volume.

However, in the preferred embodiment, the thermochemical treatment of the copper-based alloy is performed after composing with the backing metal layer. By way of example, the layer of layered metal can be poured directly onto the support metal layer or the intermediate layer which may be present, whereby the integration of the method into existing processes in the plain bearing industry is easier. It can thus be achieved a corresponding cost advantage.

The at least one oxidizing agent can be used solid and / or gaseous or plasma-shaped. The use of a solid oxidizing agent has the advantage that specifically only at least one volume range of the sliding layer can be oxidized. The use of a plasma-shaped oxidant in turn has the advantage that the oxidation can take place very rapidly, as a result of which the duration of the process can be shortened. As with plasma-shaped oxidizing agents, it is relatively easy to apply the oxidant to the entire surface with a gaseous oxidizing agent, so that the precipitates can be produced relatively quickly by diffusion in the underlying partial layer. Gaseous (non-plasma) oxidants have the part before that the concentration of the oxidizing agent in the oxidation atmosphere can be easily adjusted and regulated.

To accelerate the generation of the precipitates and thus to shorten the process duration, it may be provided that the thermochemical treatment is carried out at a temperature which is selected from a range of 500 ° C to the solidification temperature of the copper-based alloy. In addition, the height of the treatment temperature can influence the particle size of the precipitates, since coagulation of the precipitates can be effected with higher temperatures.

According to another embodiment of the method can be provided, the gaseous oxidant used in the oxidation atmosphere with a partial pressure of at least 1.10-3 atm and a maximum of 3 atm is used. As with the temperature, the particle size can also be influenced by the pressure, but with increasing pressure the precipitations become smaller. At a partial pressure of less than 1.10'3 atm, particles which are too small thus result in an improvement in the tribological properties of the copper-based alloy, but to a lesser extent. At a partial pressure of greater than 3 atm, on the other hand, there is the danger that a stable, firmly adhering oxide layer is formed on the surface of the sliding layer, which would also adversely affect the tribological properties of the copper-based alloy.

According to a variant embodiment of the sliding bearing, it can be provided that the precipitates have a maximum particle size of at most 50 μm, the precipitations having a maximum particle size between 0.1 μm and 20 μm, according to a preferred embodiment. Fine-grained precipitates are therefore preferred, since with the same amount of precipitates in the copper-base alloy a more homogeneous distribution of the precipitates within the sublayer and less tendency to seize the overlay can be achieved. In addition, it has been observed that the self-lubricating properties of the precipitates are improved when the precipitates have a particle size between 0.1 pm and 50 pm.

It is also possible that the precipitates have a maximum particle size, which decreases gradually in the direction from the surface of the copper-based alloy on the support metal layer, whereby within the sub-layer, a gradual change, in particular increase, the hardness of the sub-layer can be achieved. The sliding layer can thus be optimized in terms of lubricating properties in the area of the surface. In the direction of the support layer, on the other hand, the copper-base alloy can be hardened due to the finer precipitates, whereby the loadability of the sliding layer can be improved.

Also, for improving the lubricating properties of the copper-base alloy in the area of the surface, it may be provided that the number of precipitates in the direction from the surface of the copper-base alloy to the supporting metal layer gradually decreases. Due to the lower number of precipitates in deeper layer planes of the sliding layer, a smaller decrease in the hardness of the copper-base alloy in these deeper layer planes can be achieved.

The layer thickness of the partial layer of the copper-based alloy is preferably between 10 pm and 1000 pm. Although an improvement in the tribological properties of the copper-based alloy can also be achieved with a layer thickness of less than 10 μm, the long-term use properties of the sliding layer and thus also those of the sliding bearing element suffer with such low layer thicknesses. In the case of layer thicknesses of more than 1000 μm, on the other hand, the process duration is lengthened too much, as a result of which the economy of the method for producing the sliding bearing element suffers. Moreover, the decrease in the non-oxidized residual part layer of the sliding layer reduces too much the bearing capacity of the sliding layer due to the hardness drop due to the precipitations.

For a better understanding of the invention, this will be explained in more detail with reference to the following figures.

In part, in a simplified, schematic representation:

Figure 1 is a slide bearing element in side view.

FIG. 2 is a side view of a detail of the sliding layer of a variant of the sliding bearing element; FIG.

3 is a side view of a section of the sliding layer of a further embodiment of the sliding bearing element;

4 shows a detail of the sliding layer of another embodiment of the sliding bearing element in side view;

5 shows a scanning electron micrograph of a sliding layer in the region of the thermochemically treated partial layer;

6 shows a scanning electron micrograph of the sliding layer according to FIG. 5 in the region of the thermochemically treated partial layer in a larger magnification;

7 shows a light microscope photograph of another sliding layer.

By way of introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component names, the disclosures contained in the entire description can be mutatis mutandis to the same parts with the same reference numerals or component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and these position information in a change in position mutatis mutandis to transfer to the new location.

In Fig. 1, a sliding bearing element 1, in particular a radial sliding bearing element, made of a composite material in side view.

The sliding bearing element 1 is provided in particular for use in an internal combustion engine or for supporting a shaft.

The sliding bearing element 1 has a sliding bearing element body 2. The sliding bearing element body 2 comprises a supporting metal layer 3 and a further layer 4 arranged thereon or consists of the supporting metal layer 3 and the further layer 4 connected thereto.

As indicated by dashed lines in FIG. 1, the sliding bearing element body 2 can also have additional layers, for example a bearing metal layer 5, which is arranged between the further layer 4 and the supporting metal layer 3, and / or an inlet layer 6 on the further layer 4. Between at least two of the layers of the plain bearing element 1, at least one diffusion barrier layer and / or at least one bonding layer can also be arranged.

Since the basic structure of such multi-layer sliding bearing elements is known from the prior art, reference is made to the relevant literature on details of the layer structure.

Likewise, the materials used, from which the support metal layer 3, the bearing metal layer 5, the inlet layer 6, which may consist of at least one diffusion barrier layer and the at least one bonding layer, from the prior art, and therefore reference is made to the relevant literature with respect to this. By way of example, the support metal layer 3 is made of a steel, the bearing metal layer 5 of a copper alloy with 5% by weight of tin and the remainder copper, the inlet layer of tin or bismuth or of a synthetic polymer containing at least one additive, the bonding layer made of copper or nickel, may be formed.

The half-shell-shaped plain bearing element 1 forms together with at least one other sliding bearing element 7 - depending on the structural design can also be present more than another sliding bearing element 7 - a sliding bearing 8. In this case, the lower plain bearing element is preferably formed in the installed state by the sliding bearing element 1 according to the invention. But there is also the possibility that at least one of the at least one further Gleitlagerele elements by the sliding bearing element 1 or the entire sliding bearing 8 is formed from at least two sliding bearing elements 2 according to the invention.

It is also possible that the sliding bearing element 1 is designed as a plain bearing bush, as indicated by dashed lines in Fig. 1. In this case, the sliding bearing element 1 at the same time the sliding bearing. 8

Furthermore, it is possible for the layer 4 to form a direct coating, for example a radially inner coating of a connecting-rod eye.

Next, the sliding bearing element 1 and the sliding bearing 8 in the form of a thrust washer, etc., may be formed.

The layer 4 is formed as a sliding layer 9. For this purpose, a first embodiment of this sliding layer 9 is shown in FIG.

The sliding layer 9 consists of a casting alloy of a copper-based alloy. The copper-based alloy is in particular a bronze. However, other copper base alloys are also usable for the sliding layer 9, for example brass, red brass, although this is not the preferred embodiment of the invention.

The copper-base alloy includes, in addition to copper, one or more of the elements selected from the group consisting of boron, antimony, aluminum, silicon, vanadium, phosphorus, titanium, manganese, tin, zinc, magnesium. Since the primary effects of the individual elements are known in prior art copper base alloys, reference is made thereto. In the preferred embodiment variant, however, the copper-based alloy contains, in addition to copper, at least tin and optionally at least one of the further elements mentioned above.

The possible proportions of the individual elements on the copper-base alloy are summarized in Table 1. The percentages for the proportions in Table 1, as throughout the specification, are to be understood as weight percent unless expressly stated otherwise. It should be noted that these proportions do not include the proportions of the oxidized metals. These are shown in Table 2.

For each copper-based alloy, copper forms the remainder, with the proportion of copper depending on the proportion of one or the sum of the several elements from the specified group.

Table 1: Quantity ranges of the alloying elements of the copper-base alloy

As can be seen from FIG. 2, 9 precipitates 10 are contained in the sliding layer. These precipitates 10 are formed from at least one alloying constituent and have at least one of the constituents of the alloy. The precipitates 10 are monovalent or polyvalent oxides of at least one of the alloying constituents of the copper-base alloy. The valency refers to the respective element involved in the reaction, which is oxidized. There are also mixed oxides possible.

As apparent from the method explained below, the precipitates 10 of the copper-base alloy are not added as such, but the precipitates of at least one alloying ingredient are generated due to an oxidation reaction.

It should already be noted that the term "oxidation", according to the general definition, means the release of electrons in the course of a chemical reaction. For example, MgO reacts with oxygen to give MgO by donating two electrons.

The sliding layer 9 has a layer thickness 11. The layer thickness 11 is in particular between 0.1 mm and 1.5 mm.

As can be seen from FIG. 2, the precipitates 10 are not distributed over the entire layer thickness 11 of the sliding layer 9, but their arrangement or design is limited only to a region within a partial layer 12 of the sliding layer 9. The precipitates 10 are within , In particular, only within, this sub-layer 12 is arranged. Owing to the chosen procedure, oxides which form on the surface of the sliding layer 9 by the oxidation do not form a firm bond with the copper-base alloy, so that these oxides can flake off or be easily removed.

The precipitates 10 are predominantly in the grains of the copper base alloy. By the term "predominantly" is meant that at least a proportion of 60% of the precipitates 10, based on the totality of the precipitates 10, is in the grains of the copper-based alloy. The rest is in the grain boundaries.

In the embodiment of the sliding layer 9 according to FIG. 2, the precipitates are distributed relatively uniformly over the entire volume of the partial layer 12. By the term "relatively uniform" is meant that the difference in the number of precipitates 10 of each two different volume regions of the sub-layer 12 by not more than 5%, in particular by not more than 3%, from each other, being used as a reference value with 100% is a number of precipitates 10 in a volume region of the sub-layer 12, which is calculated from the total number of precipitates 10 in the total volume of the sub-layer 12 divided by the number of volume regions comprising the total volume.

However, it is also possible that the number of precipitates 10 gradually decreases in the direction from the surface 13 of the copper base alloy of the sliding layer 9 to the supporting metal layer 3, as schematically shown in FIG.

It should be noted that FIGS. 2 to 4 each show, if appropriate, separate embodiments of the slide bearing element 1, wherein the same reference numerals or component designations are used for the same parts. In order to avoid unnecessary repetition, reference is made respectively to the detailed description of the entire figures.

By reducing the number of precipitates 10 in the sub-layer 12 in the direction of the support metal layer 3, a Flärtgradient the sub-layer 12 and thus in the sliding layer 9 can be adjusted.

However, it is also possible that the number of precipitates 10 in the sub-layer 12 gradually decreases or generally varies in the direction from the surface 13 of the copper-base alloy of the sliding layer 9 to the supporting metal layer 3.

In general, the concentration of the precipitates 10 in the partial layer 12 can be between 1% by weight and 25% by weight, in particular between 3% by weight and 20% by weight, preferably between 3% by weight and 15% by weight. %. At a concentration of more than 25 wt .-%, there is a risk of brittle fracture due to the increased brittle phase content. If the concentration drops below 1% by weight in the partial layer 12, although a slight reduction in the tendency to eat of the sliding layer 9 is still observed, the reduction of the tendency to eat is at least 1% by weight, in particular at least 3% by weight, much better. In the event that a concentration gradient of precipitates 10 is formed in the partial layer 12 (FIG. 3), this can be designed such that the proportion of the precipitates 10 in the region of the surface 13 of the sliding layer 9 is between 1% by weight and 20 Wt .-%, in particular between 1 wt .-% and 15 wt .-%, and in the direction of the support metal layer 3 to a value between 0 wt .-% and 3 wt .-%, in particular between 0 wt .-% and 1 wt .-%, decreases. To determine these values, the partial layer 12 is subdivided in the direction of the supporting metal layer 3 into ten subpart layers.

In general, the partial layer 12 may have a layer thickness 14 (FIG. 2) which is between 1% and 66%, in particular between 3% and 50%, of the layer thickness 11 of the sliding layer 9. Preferably, the layer thickness 14 of the sub-layer 12 is between 0.1 mm and 1.5 mm, in particular between 150 μιτι and 500 μιτι. Surprisingly, it has been shown in the course of investigations that it is sufficient for the reduction of the tendency to eat of the lead-free sliding layer 9 when the precipitates 10 are not distributed over the entire layer thickness 11 of the sliding layer 9, but the precipitates 10 are limited to the partial layer 12 ,

The partial layer 12 may be formed immediately adjacent to the surface 13.

In general, the precipitates 10 may have a maximum particle size 15 (FIG. 2) of at most 50 μm, in particular between 0.1 μm and 20 μm. Preferably, the maximum particle size 15 is between 15 μιτι and 20 μιτι. The maximum particle size 15 is understood to mean the largest dimension that a particle has.

It is possible in this case for the particle size 15 of the precipitates 10 to remain substantially constant over the entire volume of the partial layer 10, i. that the maximum particle sizes 15 of the precipitates 10 differ by no more than 15%, in particular not more than 10%.

On the other hand, according to another embodiment of the sliding element 1, it is possible, as shown in FIG. 4, for the precipitates 10 to have a maximum particle size 15 which gradually increases in the direction from the surface 13 of the copper-base alloy to the supporting metal layer 3. In this case, the particle size 15 of the precipitates 10 can be increased by a value selected from a range of 0.1% to 80%, in particular from a range of 0.1% to 70%, based on the particle size 15 of the precipitates 10 in the range the surface 13.

However, it is also possible for the precipitates 10 to have a maximum particle size 15 which gradually decreases or generally varies in the direction from the surface 13 of the copper-base alloy to the support metal layer 3. In this case, the particle size 15 of the precipitates 10 can decrease by a value which is selected from a range of 0.1% to 80%, in particular from a range of 0.1% to 70%, based on the particle size 15 of the precipitates 10 im Area of the surface 13.

The habit of the precipitates 10 may be at least approximately spherical, at least approximately ellipsoidal or egg-shaped, bulbous, at least approximately cubic, etc., or completely irregular. Preferably, the precipitates 10 are at least approximately round or at least approximately ellipsoidal.

As already mentioned, the precipitate 10 is preferably produced only after the casting of the sliding layer 9 or the copper-based alloy by oxidation. The precipitates 10 are therefore not added as such to the starting materials of the copper-based alloy.

In a first step, a starting material of at least two layers is produced for the production of the sliding bearing element 1. For this purpose, in the simplest case, a copper-based alloy is poured onto a metal strip, in particular a flat metal strip, or a metal sheet, in particular a flat metal sheet.

In this case, the metal strip or metal sheet forms the support metal layer 3. In the event that flat metal strips or metal sheets are used, they are converted in a later process step nor to the respective plain bearing element 1, as is known per se from the prior art.

As already mentioned above, the plain bearing element 1 can also have more than three layers. In this case, the copper-based alloy may be cast on the uppermost layer of the composite material with the support metal layer, or another composite material, especially two-layer composite material, may be produced which is subsequently bonded to the support metal layer or a composite material comprising the support metal layer, for example by roll-plating.

The casting of the copper-based alloy onto the metal strip or the metal sheet or onto a layer of a composite material may, for example, take place by means of horizontal or vertical strip casting.

But it is also possible that a copper-based alloy is produced in a first step, for example by means of continuous casting and the solidified copper-based alloy is then connected to at least one of the other layers of the sliding bearing element 1, in particular the support metal layer 3, for example by means of roll cladding.

According to another embodiment, it is possible that the sliding bearing elements 1 is produced by a centrifugal casting process. In this case, preferably no thermomechanical treatment is carried out.

The proportions of metallic and optionally non-metallic components in the starting mixture used for the Fierstellung of the sliding layer 9 are selected according to the information in Table 1, plus the proportions of these components, which are consumed during the oxidation to the precipitates 10.

The casting of alloys from the melt is known in principle to the sliding bearing expert, so that with regard to the parameters, such as temperature, etc., reference is made to the relevant prior art.

After the composite material has been produced from at least two layers, the precipitates 10 are produced in the sliding layer 9 from the solidified copper-base alloy. These precipitates 10 are produced from at least one of the components of the copper-based alloy. To this end, after solidification, the copper-base alloy is thermochemically treated, contacting the copper-based alloy with at least one oxidizer, and oxidizing the oxidizer into the copper-based alloy such that at least one alloying constituent of the copper-base alloy is at least partially oxidized to form the precipitates 10 within the copper-base alloy ,

At least one element from a group comprising oxygen and oxygen-releasing compounds is preferably used as the oxidizing agent, so that oxides are formed as precipitates. It is also possible to use a mixture of different oxidizing agents or the copper-based alloy can also be treated repeatedly with at least one oxidizing agent, for example in successive process steps, each with an oxidizing agent.

The at least one oxidizing agent may be, for example, oxygen, water vapor or ozone.

Preferably, the at least one oxidizing agent is used in gaseous or plasma form. For this purpose, the composite material is brought into contact with the cast copper-base alloy in a, in particular closed on all sides, treatment chamber with the oxidizing agent, in which the oxidizing agent is introduced into the atmosphere of the treatment chamber. Optionally, by means of a regulation, the proportion of the oxidant consumed over the time of treatment can be automatically supplemented by a fresh oxidant in the treatment chamber so that an at least approximately equal partial pressure prevails in the treatment chamber on the oxidant.

However, it is also possible to deliberately change the partial pressure of the oxidizing agent in the treatment chamber over the time of treatment of the composite material, for example to form a concentration gradient of the precipitates 10 over the layer thickness 14 of the partial layer 12, as stated above.

In general, the partial pressure of the gaseous or plasma oxidant used in the oxidation atmosphere may have a partial pressure of at least 1.10'5 atm and of at most 5 atm, in particular of at least 1.10 3 atm and at most 3 atm. The remaining portion of the oxidizing atmosphere preferably forms an inert gas, such as argon, helium, or nitrogen. But it is also possible that the remaining portion of the oxidation atmosphere is formed by air.

The temperature at which this thermochemical treatment is carried out is preferably selected from a range of 500 ° C, especially 600 ° C, to the solidification temperature of the respective copper base alloy.

The duration of the thermochemical treatment can be selected from a range of 1 hour to 96 hours, especially from a range of 3 hours to 48 hours.

In the method variant just described, the production of the precipitates 10 takes place after the composite formation of the copper-base alloy with at least one further layer. However, according to a variant embodiment of the method, it is also possible for the thermochemical treatment of the copper-base alloy to be carried out before the composite formation with at least one further layer of the plain bearing element 1, in which case the same process parameters can be used.

According to a further embodiment variant of the method it can be provided that the at least one oxidizing agent is used firmly. In this case, for example, the oxidizing agent may be applied to at least a part of the surface of the copper-base alloy. The treatment temperature and the duration of treatment can be selected from the ranges mentioned above.

As the solid oxidizing agent, an oxide powder or mixtures of various oxide powders may be used. Possible oxide powders are, for example, BaO 2, ΚΜηθ 4, KNO 3, KClO 3, K 2 CrO 4.

According to a further embodiment variant of the method, provision can be made for thermomechanical treatment of the solidified copper-base alloy to be carried out before or simultaneously with the thermochemical treatment. The thermomechanical treatment may be for example a rolling, forming or forming.

The temperature of the thermomechanical treatment can be selected from a range of 450 ° C to 1000 ° C, especially from a range of 750 ° C to 950 ° C.

The duration of the thermo-mechanical treatment may be selected from a range of 3 hours to 25 hours, especially from a range of 5 hours to 20 hours.

Due to the thermomechanical treatment of the copper-based alloy, a more permeable structure can be produced by increasing the fraction of grain boundaries. In addition, it can also be used to increase the toughness of the copper-based alloy.

From the composite material is then finally the sliding bearing element 1 by optionally forming strips of a plate material and by appropriate deformation, for example in a half-shell mold, and optionally finishing operations such. Fine boring, etc. produced. These final processing steps are known to the sliding bearing specialist, so that reference is made to the relevant literature.

As already mentioned, as a result of the thermochemical treatment of the copper-base alloy, oxide precipitates 10 are produced. Table 2 below shows such precipitates 10 together with the (preferred) proportions of the copper base alloy. Again, they are quantities in wt .-% to understand. Furthermore, the proportions are based on the particular cation of the compounds, since other than the exemplified oxides can be produced. By referring to the respective cation, the quantities are also valid for these oxides not listed in Table 2.

Generally, the cumulative amount of precipitates 10 in the copper base alloy of the sliding layer 9 can be selected from a range of 1% by weight and 25% by weight, especially from a range of 3% by weight to 20% by weight.

Table 2: Quantities of the precipitates in the sliding layer 9

The proportions and size of the precipitates 10 may be affected by the concentration of the oxidizing agent and / or the treatment temperature and / or the treatment time. Furthermore, by varying the concentration of the oxidizing agent and / or the treatment temperature over the duration of the treatment, the abovementioned concentration gradient of the precipitates 10 over the layer thickness 14 of the partial layer 12 of the copper-base alloy can be adjusted. By way of the concentration of the oxidizing agent, the particle size 15 of the precipitates and thus also the gradient in the particle size 15 can be influenced via the layer thickness 14 of the partial layer 12 of the copper-base alloy, as has already been explained above.

The following are some of the experiments performed.

Example 1:

An alloy containing 96% by weight of copper, 3% by weight of tin and 1% by weight of zinc was poured onto a support metal layer 3 made of a steel 220 mm wide and 4 mm thick by means of strip casting. The preheated steel had a temperature of 1070 ° C and a speed of 6 cm / min. On top of this, the casting alloy is poured at a temperature of 1170 ° C. The steel is cooled by means of oil cooling from below to 100 ° C and solidified with the cast alloy in the composite. This composite was a thickness reduction of min 25% and max. 60% subjected to rolling. Thereafter, this material was thermochemically treated by air at 900 ° C for 24 hours.

This resulted in a partial layer 12 with a layer thickness 14 of approximately 250 μιτι. Analysis of the copper-based alloy in the sub-layer 12 revealed 88.5 wt% copper, 7.5 wt% tin, 1 wt% zinc, and 3 wt% oxygen. As precipitates 10 so tin oxide (s), zinc oxide (s) and mixtures thereof have formed.

FIGS. 5 and 6 show the scanning electron micrographs of the copper-based alloy for this purpose. Clearly visible are the precipitates 10 as bright "dots" within the sub-layer 12 of the copper-base alloy. The dots with a dark "core" are oxides on which other oxides are grown.

The predisposition of this copper-based alloy was determined after a predisposition test. It was found a value of 57 MPa.

In comparison, a lead-containing bronze with 20 wt .-% lead to a predisposition of 62 MPa.

The same unoxidized sample, on the other hand, has only a predilection of 35 MPa. Example 2:

An alloy was cast with 92 wt.% Copper and 7 wt.% Tin and 1 wt.% Zinc.

Thereafter, this material was thermochemically treated by air at 950 ° C for 12 hours. This resulted in a partial layer 12 with a layer thickness 14 of approximately 130 μm. The photomicrograph (FIG. 7) shows the resulting partial layer 12 and the resulting precipitates 10 (tin oxides, zinc oxides and their mixed oxides) as dark "dots".

Further examples:

The following table summarizes further examples of precipitates 10 in sliding layers 9. The quantities are to be understood as wt .-%.

Table 3: Example Compositions of Slide Layer 9:

The embodiments show possible embodiments of the sliding bearing element 1, wherein it should be noted at this point that also various combinations of the individual embodiments are possible with each other.

For the sake of the order, it should finally be pointed out that, for a better understanding of the construction of plain bearing element 1, this or its constituent parts have been shown partly unevenly and / or enlarged and / or reduced in size

REFERENCE SIGNS LIST 1 sliding bearing element 2 sliding bearing element body 3 supporting metal layer 4 layer 5 bearing metal layer 6 inlet layer 7 sliding bearing element 8 slide bearing 9 sliding layer 10 precipitation 11 layer thickness 12 partial layer 13 surface 14 layer thickness 15 particle size

Claims (15)

claims 1. A method for producing a sliding bearing element (1) according to which a composite material of a first layer and one or more further layer (s) is produced, wherein the further layer or one of the further layers is formed as a sliding layer (9), and as a sliding layer (9) a cast alloy is prepared from a lead-free copper-base alloy, wherein precipitates (10) having at least one alloy constituent of the copper-base alloy are incorporated in the copper-base alloy, characterized in that the copper-based alloy is thermochemically treated after solidification, the copper-based alloy having at least one Oxidizing agent is brought into contact, and the oxidizing agent is diffused into the copper-based alloy, so that at least one alloying constituent of the copper-based alloy is at least partially oxidized to form the precipitates (10) within the copper-based alloy, wherein the Ausscheidun gene (10) are formed only within a partial layer (12) of the copper-based alloy. 2. The method according to claim 1, characterized in that at least one element from a group comprising oxygen and oxygen-releasing compounds is used as the oxidizing agent. 3. The method according to claim 1 or 2, characterized in that before or simultaneously with the thermochemical treatment, a thermomechanical treatment of the solidified copper-based alloy is performed. 4. The method according to any one of claims 1 to 3, characterized in that a copper-based alloy is used, the one or more of the elements from a group comprising boron, antimony, aluminum, silicon, vanadium, phosphorus, titanium, manganese, tin, zinc, Has magnesium. 5. The method according to any one of claims 1 to 4, characterized in that the thermochemical treatment of the copper-based alloy is carried out prior to the composite formation with the layer of the support metal. 6. The method according to any one of claims 1 to 4, characterized in that the thermochemical treatment of the copper-based alloy is carried out after the composite formation with the layer of the support metal. 7. The method according to any one of claims 1 to 6, characterized in that the at least one oxidizing agent is used solid and / or gaseous or plasma-shaped. 8. The method according to any one of claims 1 to 7, characterized in that the thermochemical treatment is carried out at a temperature which is selected from a range of 500 ° C to the solidification temperature of the copper-based alloy. 9. The method according to claim 7 or 8, characterized in that the gaseous oxidant used in the oxidation atmosphere with a partial pressure of at least 1.10'3 atm and a maximum of 3 atm is used. 10. sliding bearing element (1) made of a composite material comprising a support metal layer (3) and a sliding layer (9) and optionally an intermediate layer between the support metal layer (3) and the sliding layer (9), wherein the sliding layer (9) made of a casting alloy of a lead-free A copper-base alloy is formed in which precipitates (10) containing at least one alloying constituent of the copper-base alloy are contained, characterized in that the precipitates (10) are formed only within a partial layer (12) of the copper-base alloy. 11. plain bearing element (1) according to claim 10, characterized in that the precipitates (10) have a maximum particle size (15) of a maximum of 50 pm. 12. plain bearing element (1) according to claim 11, characterized in that the precipitates (10) have a maximum particle size (15) between 0.1 pm and 20 pm. 13. plain bearing element (1) according to one of claims 10 to 12, characterized in that the precipitates (10) have a maximum particle size (15), which gradually decreases in the direction of a surface (13) of the copper-based alloy on the support metal layer (3) , 14. plain bearing element (1) according to any one of claims 10 to 13, characterized in that the number of precipitates (10) gradually decreases in the direction of the surface (13) of the copper-based alloy on the support metal layer (3). 15. plain bearing element (1) according to one of claims 10 to 14, characterized in that a layer thickness (14) of the sub-layer (12) of the copper-based alloy is between 10 pm and 1000 pm.