Coated bearing component

Abstract

A bearing component (1) of a bearing assembly, in particular a rolling bearing assembly, is disclosed, wherein the bearing component (1) is made of steel, in particular rolling bearing steel. The bearing component (1) has a layer system (6) which is applied to a surface (4) of the bearing component (1), wherein the layer system (6) comprises nickel and tin.

Description

[0001] 2024P00257DE

[0002] bearing component

[0003] Technical field

[0004] The present invention relates to a bearing component of a bearing assembly, in particular a rolling bearing assembly, according to the preamble of claim 1.

[0005] Technical background

[0006] Bearing components, such as bearing rings or rolling elements, are often coated to protect their surfaces or add additional functionality. For example, the surfaces can be provided with a corrosion-resistant layer, which may contain zinc or other suitable elements.

[0007] Bearing components, however, are constantly facing new challenges related to new applications. For example, these components may be used in environments where they come into contact with new refrigerants, such as in compressors, with oxygen diluted by such refrigerants, or with ammonia attack and hydrogen absorption, such as in hydrogen and fuel production plants. The coatings used on bearing components to date are not suitable for such applications, which is why the service life of bearing components used in these environments is significantly reduced.

[0008] For example, zinc-containing coatings such as Zn, ZnNi, ZnFe are a proven protective system in humid environments with a neutral pH, but can exhibit high reactivity and self-dissolution or rapid corrosion under non-neutral pH values ​​or in certain chemically aggressive environments. Non-reactive coatings such as hard chrome may offer better chemical resistance, but on rolling bearing raceways, they may tend to flake off, have a microcracked structure due to the manufacturing process, or develop one during operation. Some such non-reactive coatings may require surface pretreatment such as fine blasting or etching. Such pretreatments can be detrimental to the quality of, for example, a rolling bearing raceway. Therefore, the object of the present invention is to provide a bearing component suitable for use in aggressive environments containing refrigerants, ammonia, hydrogen, or similar substances.suitable for hydrogen-based fuels, corrosive liquids, corrosive gases or similar substances.

[0009] Summary of the invention

[0010] This problem is solved by a bearing component according to claim 1.

[0011] Accordingly, a bearing component of a bearing assembly, in particular a rolling bearing assembly, is proposed. The bearing component can be, for example, bearing rings or rolling elements. Furthermore, the bearing assembly can also be a plain bearing. The bearing component is made of steel, in particular bearing steel. This means that the main material of the bearing component is steel and can therefore be damaged, for example by corrosion, when used in aggressive environments containing hydrogen, ammonia, or refrigerants.

[0012] The bearing component therefore has a layer system applied to its surface, wherein the layer system comprises nickel and tin. It has been shown that the combination of nickel and tin forms a particularly stable protective layer that can withstand even aggressive environments. Preferably, the layer system is applied to the entire surface of the bearing component in order to completely encapsulate and protect it.

[0013] Nickel has a very dense structure and is therefore particularly suitable for shielding the main material of the bearing component. Furthermore, nickel adheres well to steel, thus ensuring the durability of the coating system on the steel of the bearing component.

[0014] Furthermore, nickel has a medium hardness that is sufficient for rolling or sliding contact.

[0015] Tin, on the other hand, has high chemical resistance to several substances that can be present in the aggressive environments of typical modern applications, such as ammonia. Furthermore, tin possesses metallic dry-lubricating properties. This allows it to provide additional lubrication support for the bearing component (e.g., as emergency lubrication). A combination of nickel and tin in the coating system can thus utilize the advantages of both materials and provide a stable coating for the bearing component, which can also serve as corrosion protection. In particular, the coating system serves not only to provide conventional corrosion protection but also corrosion protection against chemical substances that are not limited to water or salt water.A bearing component coated in this way can therefore be used, for example, in pumps and compressors where an atmosphere containing ammonia or ammonia compounds is present. Such applications have multiplied, for example, in the context of hydrogen-based liquid fuel production.

[0016] According to one embodiment, the coating system includes a corrosion protection layer consisting of a tin-nickel alloy (SnNi alloy). In this case, the coating system thus comprises nickel and tin combined in one alloy. The alloy can contain tin (Si) and nickel (Ni) in a ratio of 6:4 (Si) to 7:3 (Ni), in particular 6.5:3.5 to 6.8:3.2, preferably 6.7:3.3.

[0017] Such an alloy has the advantage of being relatively chemically resistant due to the tin, and particularly resistant to ammonia. Nickel, on the other hand, provides resistance to general corrosion, but not to ammonia. In an alloy, the individual properties of the components do not simply mix, but rather combine in an optimized new way. The alloy is therefore universally resistant, better than the individual components combined. Pure tin would be too soft and would wear down in bearings; however, the combination with nickel makes the alloy harder. Furthermore, the tin content of the alloy can, at least to some extent, act as a dry lubricant.

[0018] The deposition of the tin-nickel alloy is preferably carried out with high layer purity (i.e., without or at least with few impurities or inclusions) and a uniform microstructure (i.e., a uniform layer without defects). Defective areas, e.g., sphere boundaries, pores, or impurity inclusions, would contribute to an uneven charge distribution and an uneven surface potential.

[0019] The electrical surface potential of the deposited tin-nickel alloy proposed here, when measured using atomic force microscopy (AFM) or scanning Kelvin (probe) force microscopy (SKPFM), preferably has a peak distribution value between 120 and 140 mV. A less pure or more uneven tin-nickel alloy would, for example, have a much higher peak distribution value, typically between 230 and 280 mV.

[0020] An electrochemical analysis using the open-circuit potential (OCP) and potentiodynamic polarization (PDP) with a 3.5% NaCl electrolyte at ambient temperature with one hour of OCP and a sampling rate of 1 mV / s has shown that the corrosion potential of the tin-nickel alloy described here against Ag / AgCl is typically in the range of -180 to -190 mV for a high layer purity and uniform microstructuring, while a less carefully produced layer can have -330 to -400 mV.

[0021] Similarly, the measurement of the corrosion current density shows that a good tin-nickel alloy layer only has a current of 0.02-0.09 pA / cm². 2 exhibits 0.35-1.05 pA / cm², while a less carefully produced layer shows 0.35-1.05 pA / cm². 2 a tin-nickel alloy layer with the first values ​​(i.e., the values ​​of a good tin-nickel alloy layer) is, for example, suitable for use in rolling bearings.

[0022] According to another embodiment, the layer system between the corrosion protection layer and the surface of the bearing component has a nickel layer.

[0023] In addition to the tin-nickel alloy layer, a nickel layer is therefore provided between the alloy layer and the main material of the bearing component.

[0024] Such a nickel layer, especially an electrolytic nickel layer, also called nickel strike, stop nickel, or Woods strike, increases the adhesion of the tin-nickel alloy to the steel surface of the bearing component. The tin-nickel alloy can thus, for example, better withstand rolling or sliding contact without adhesion problems.

[0025] Here, the electrolytic nickel layer is first applied to the steel surface of the bearing component, and the tin-nickel alloy is then deposited on top. Nickel Strike is a special nickel deposition process using an electrolyte based on...

[0026] Nickel chloride, nickel sulfate, and boric acid are deposited at a pH of approximately 3. The deposition is extremely thin, for example, between 0.2 and 1 pm, occurs very rapidly, and does not damage the substrate, i.e., the steel of the bearing component, but rather promotes maximum adhesion. The adhesion of SnNi to Ni and Ni to Fe (iron, i.e., the main component of the steel of the bearing component) is higher than that of SnNi to Fe.

[0027] Additionally, this has the advantage that the nickel layer acts as an intermediate layer between the tin-nickel alloy and the steel, thus shielding the steel from the tin-nickel electrolyte. The electrolyte required for depositing the tin-nickel alloy could potentially damage or attack the steel of the bearing component, which is prevented by the nickel strike process. The tin-nickel electrolyte has a composition that is highly aggressive towards steel and can dissolve the steel surface. Direct coating can therefore result in significant roughening of the steel surface, which, while not detrimental to coating adhesion, can impair the dimensional accuracy of a surface suitable for rolling bearing raceways and can also lead to microstructural damage, which can be particularly exacerbated in rolling contact areas.If the nickel strike is applied to the steel before the bearing component is immersed in the tin-nickel electrolyte, then this thin nickel layer provides sufficient protection against the attack of the tin-nickel electrolyte on the steel.

[0028] The coating system, which in the case described here consists of a thin nickel layer plus a tin-nickel alloy layer, preferably has a total thickness in the range of 2 to 6 pm, particularly 3 to 5 pm. Furthermore, the coating system offers strong corrosion protection against many chemical attacks, including ammonia.

[0029] According to another alternative embodiment, the layer system, instead of a corrosion protection layer in the form of an alloy, features a corrosion and diffusion protection layer of pure nickel deposited from a nickel sulfamate electrolyte. When nickel is deposited using a nickel sulfamate electrolyte (also called sulfamate vemickeletons), a pure and ductile nickel layer, also called pure nickel, is obtained—that is, a layer containing only nickel without any other substances. This nickel sulfamate electrolyte can produce a clean and sulfur-free nickel layer. This particularly pure nickel deposition, which is only possible with sulfamate vemickeletons, has the advantage that, in addition to its corrosion protection effect, the nickel layer also provides a diffusion barrier function, which can, for example, protect the bearing component, or its main material, from hydrogen.

[0030] However, the pure nickel layer can exhibit poor resistance, particularly to ammonia. Therefore, in a further embodiment, the coating system can include a tin layer applied over the pure nickel layer. This tin layer provides protection against ammonia and also serves as a metallic dry lubricant. In this way, any potential lubrication deficiencies caused by the tin layer can be reduced, and hydrogen embrittlement during operation can be minimized by the underlying pure nickel layer. Simultaneously, the tin layer protects the pure nickel layer from chemical attack, for example, by ammonia. Furthermore, the tin layer according to this embodiment has the advantage of being soft and therefore remaining crack-free, even under stress and during operation.Thus, the protective effect of the tin on the pure nickel layer is limited only by the gradual erosion of the tin layer, but not by premature permeability of the tin layer.

[0031] If a hard layer, such as a chromium layer, were applied to the nickel layer, this hard layer could be affected by the elastic deformation of the substrate, i.e., the steel and the nickel layer. The tin layer, on the other hand, can adapt to the elasticity of the underlying layers due to its softness. Furthermore, the layer thickness tolerances increase with each coating step. Since the pure nickel layer has a high deposition rate and low dispersion, its thickness can already be quite considerable. Therefore, it is advantageous that the tin layer is soft and deformable, and can be plastically adjusted to the appropriate thickness by the bearing itself during operation under load.

[0032] Furthermore, tests have shown that the electrical surface potential signals measured with AFM / SKPFM for the combination of a nickel layer with a tin layer applied to it have a peak distribution value of approximately 400 mV, in contrast to the aforementioned values ​​for the tin-nickel alloy. X-ray diffraction reveals that the tin layer exhibits peaks from a multitude of crystalline planes. The corrosion potential of the nickel layer is higher than that of the tin top layer. However, a potential drop is observed in the top layer due to the electrochemical activity of tin. Compared to uncoated carbon steel, OCP / PDP reveals a significant difference in the tin / nickel corrosion potential relative to Ag / AgCl. During a test duration of 3600 seconds, carbon steel shows a rapid drop in the curve from -430 mV to -570 mV and a further decline without reaching a stable state.Although tin / nickel also shows an initial drop from -445 mV to -500 mV, it then stabilizes at this level.

[0033] According to another embodiment, the layer system between the corrosion and diffusion protection layer made of pure nickel and the surface of the bearing component can include a nickel layer. As described above in connection with the tin-nickel alloy, a nickel strike layer can also be provided beneath the pure nickel layer to optimize the layer adhesion to the steel of the bearing component. This nickel strike layer is not mandatory, as pure nickel already exhibits good adhesion, and its electrolyte aggressiveness is significantly lower than when depositing a tin-nickel alloy. However, the more layer transitions there are between sublayers, the greater the diffusion barrier of the entire layer system becomes.

[0034] Both the tin-nickel alloy layer and the nickel-tin double layer exhibit excellent general corrosion protection properties as well as ammonia resistance. The tin-nickel alloy layer focuses on general substrate protection along with continuous wear resistance and chemical resistance across the entire layer thickness during bearing operation.

[0035] The nickel-tin double layer (pure nickel with a tin layer placed on top) provides the function of a metallic dry lubricant and a barrier function as well as a reduction of hydrogen diffusion in separate sub-layers, whereby the general corrosion protection is provided by the nickel layer and the protection of the nickel layer against e.g. ammonia is provided by the tin layer.

[0036] The total thickness of the coating system can range from 2 to 6 pm, particularly from 3 to 5 pm. This means that all layers of the coating system together, in any variant (tin-nickel alloy alone, tin-nickel alloy with nickel strike, pure nickel layer, pure nickel layer with nickel strike, pure nickel layer with a tin layer above and a nickel strike below), can have a total thickness between 2 and 6 pm. The choice of embodiment depends primarily on the bearing's application, whether it is subject to more wear-intensive continuous operation or occasional operation, the load conditions, whether there is a need for explicit emergency running properties, whether there is a risk of hydrogen embrittlement, and whether the chemical attack is better counteracted by the tin-nickel alloy layer or the nickel-tin double layer.

[0037] Further advantages and advantageous embodiments are specified in the description, the drawings, and the claims. In particular, the combinations of features specified in the description and the drawings are purely exemplary, so that the features may also exist individually or in different combinations.

[0038] Brief character description

[0039] The invention will now be described in more detail with reference to exemplary embodiments illustrated in the drawings. These exemplary embodiments and the combinations shown in them are purely illustrative and do not define the scope of protection of the invention. The scope of protection is defined solely by the appended claims.

[0040] They show:

[0041] Fig. 1: a schematic sectional view through a section of a bearing component with a first embodiment of a layer system according to a first embodiment; Fig. 2: a schematic sectional view through a section of a bearing component with a second embodiment of the layer system according to the first embodiment;

[0042] Fig. 3: a schematic sectional view through a section of a bearing component with a first embodiment of a layer system according to a second embodiment; Fig. 4: a schematic sectional view through a section of a bearing component with a second embodiment of the layer system according to the second embodiment; Fig. 5: a schematic sectional view through a section of a bearing component with a third embodiment of the layer system according to the second embodiment; and Fig. 6: a schematic sectional view through a section of a bearing component with a fourth embodiment of the layer system according to the second embodiment. Detailed description of the invention

[0043] In the following, identical or functionally equivalent elements are marked with the same reference symbols.

[0044] Fig. 1 shows a section of a bearing component 1 of a bearing assembly. The bearing component 1 can be, for example, a bearing ring of a rolling bearing or a plain bearing. Furthermore, the bearing component can be a rolling element.

[0045] The bearing component 1 has a main material 2, which is steel, in particular bearing steel. In applications with aggressive environments containing, for example, hydrogen and / or ammonia, the surface 4 of this steel material 2 is attacked.

[0046] To protect the surface 4 of the steel material 2, the bearing component 1 has a coating system 6 applied to the surface of the steel material 2. In the embodiment shown in Fig. 1, the coating system 6 comprises a tin-nickel alloy 8.

[0047] An alloy containing both tin and nickel offers the advantages of both materials: Tin is relatively chemically resistant and exhibits particularly high resistance to ammonia. Nickel is generally resistant to corrosion, but not to ammonia. Therefore, the combination of tin and nickel provides resistance to both common corrosion and ammonia. Alloy 8 is thus universally resistant, offering superior resistance compared to the individual components.

[0048] Optionally, a nickel layer 10 can be provided beneath the tin-nickel alloy 8 of the layer system 6. This layer can be used to protect the surface 4 of the steel 2 of the bearing component 1 from an electrolyte contained in the alloy 8. This nickel layer 10 can be very thin, for example, less than 1 / 2µm, since it serves only to protect the surface 4 from the electrolyte. As shown in Fig. 3, instead of a tin-nickel alloy 8 (Figures 1 and 2), the layer system 6 can also have a pure nickel layer 8'. Such a pure nickel layer 8' is produced by depositing a nickel sulfamate electrolyte. Pure nickel has proven to be particularly advantageous in hydrogen applications.

[0049] Optionally, as shown in Fig. 4, a further nickel layer 10 can be provided below this pure nickel layer 8', analogous to the embodiment of Fig. 2. This nickel layer 10 is not pure nickel, but a nickel strike. In contrast to the pure nickel layer 8', the nickel strike layer 10 may contain impurities.

[0050] Since the pure nickel layer 8' is not resistant to ammonia, a tin layer 12 can be deposited on the pure nickel layer 8', as shown in Fig. 5. This tin layer 12 provides protection for the pure nickel layer 8' against ammonia and also offers the advantage of dry lubrication.

[0051] It should be noted that Fig. 5 shows a combination of the pure nickel layer 8', the nickel strike 10, and the tin layer 12. However, it is also possible to omit the nickel strike 10 and provide only the pure nickel layer 8' and the tin layer 12, as shown in Fig. 6.

[0052] In summary, a bearing component is provided that can also be used in aggressive environments and applications that utilize, for example, ammonia or hydrogen. Previously used bearing components could not withstand these conditions; this is improved in the bearing component described here by the special layer system. Reference numeral list

[0053] 1 bearing component

[0054] 2 Steel / Main material

[0055] 4 Surface

[0056] 6-layer system

[0057] 8 Corrosion protection layer / tin-nickel alloy 8' pure nickel layer

[0058] 10 Nickel Strike

[0059] 12 tin layer

Claims

2024P00257DE Patent claims bearing component 1. Bearing component (1) of a bearing assembly, in particular a rolling bearing assembly, wherein the bearing component (1) is made of steel (2), in particular rolling bearing steel, characterized in that the bearing component (1) has a layer system (6) which is applied to a surface (4) of the bearing component (1), wherein the layer system (6) comprises nickel and tin.

2. Bearing component according to claim 1, characterized in that the layer system (6) has a corrosion protection layer (8) consisting of a tin-nickel alloy.

3. Bearing component according to claim 2, characterized in that the layer system (6) between the corrosion protection layer (8) and the surface (4) of the bearing component (1) has a nickel layer (10).

4. Bearing component according to claim 3, characterized in that the nickel layer (10) has a thickness of less than 1 pm.

5. Bearing component according to claim 1, characterized in that the layer system (6) has a corrosion protection and diffusion protection layer (8') made of pure nickel, which is deposited from nickel sulfamate electrolyte.

6. Bearing component according to claim 5, characterized in that the layer system (6) has a layer (12) which contains tin and is applied to the corrosion protection and diffusion protection layer (8').

7. Bearing component according to claim 5 or 6, characterized in that the layer system (6) between the corrosion protection and diffusion protection layer (8') and the surface (4) of the bearing component (1) comprises a nickel layer (10).

8. Bearing component according to claim 7, characterized in that the nickel layer (10) has a thickness of less than 1 pm.

9. Bearing component according to one of the preceding claims, characterized in that the total thickness of the layer system (6) is between 2 and 6 pm, in particular between 3 and 5 pm.

10. Bearing assembly comprising at least one bearing component (1) according to one of the preceding claims, wherein the bearing component (1) is a bearing ring or a rolling element.

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