Friction brake body, friction brake, and method for producing a friction brake body

Abstract

The invention relates to a friction brake body, in particular a brake disc (1), for a friction brake (2) of a motor vehicle, wherein the friction brake body comprises a base body (3) having at least one wear-resistant protective layer (5) on at least one friction contact area of ​​the base body (3), wherein the wear-resistant protective layer (5) forms a friction contact surface (4) on its side facing away from the base body (3). It is provided that the hardness of the wear-resistant protective layer (5) increases stepwise or continuously from the base body (3) to the friction contact surface (4).

Description

Technical Field

[0001] The invention relates to a friction brake body, in particular a brake disc, for a friction brake of a motor vehicle, wherein the friction brake body comprises a base body having at least one wear-resistant protective layer on at least one friction contact area of ​​the base body, wherein the wear-resistant protective layer forms a friction contact surface on its side facing away from the base body.

[0002] Furthermore, the invention relates to a friction brake for a motor vehicle, comprising at least one friction brake body formed as described above, and comprising at least one movably arranged brake shoe assigned to the friction brake body.

[0003] Furthermore, the invention relates to a method for producing the above-mentioned friction brake body. Background Art

[0004] Friction brake bodies for motor vehicles, in particular brake discs for friction brakes, are already known in the prior art. When used as intended, the friction brake body, in particular the brake disc, is connected to the vehicle wheel in a rotationally fixed manner and is arranged opposite a movable brake pad. When the brake pad presses against the friction brake body, friction is generated between the friction brake body and the brake pad (reducing the wheel's speed due to friction), thereby braking the wheel. To reduce the wear caused by friction, it is also known to apply a wear-resistant protective layer to the base body, at least in the frictional contact area interacting with the brake pad. This wear-resistant protective layer reduces wear during braking and thereby extends the service life of the friction brake body itself and the entire friction brake.

[0005] A coated brake disk is already known from the publication EP 3 034 902 A1, in which a wear protection layer with embedded ceramic particles is produced by means of laser build-up welding. Summary of the Invention

[0006] According to the disclosure, the friction brake body according to the present invention has the advantage of advantageously increasing its crack resistance. According to the present invention, this is achieved by gradually or continuously increasing the hardness of the wear-resistant protective layer from the base body to the friction contact surface. As a result, the crack resistance of the coating increases from the friction contact surface toward the base body, thereby preventing crack propagation into the base body. This results in a friction brake body that, on the one hand, has a particularly high hardness and thus wear resistance on the friction contact surface, while simultaneously possessing sufficient ductility and crack resistance to prevent cracks occurring on the friction contact surface from propagating into the base body. This allows the friction brake body to withstand thermomechanical stresses, such as those that may occur during full braking, without cracks forming in the base body or propagating into the base body, thereby improving overall mechanical strength and robustness, including corrosion resistance. Therefore, if cracks occur, in the friction brake body according to the present invention, crack propagation occurs preferentially along the hard material, since the hard material, as an inclusion, reduces the fracture toughness of the wear-resistant protective layer. Therefore, according to the present invention, crack propagation occurs more strongly in the region of the friction contact surface than in the region of the base body.

[0007] According to a preferred embodiment of the present invention, the wear-resistant protective layer has a carbide-forming element and carbon content that increases from the base body toward the friction contact surface. This results in an increase in the hardness of the wear-resistant protective layer toward the friction contact surface, as described above. In particular, carbide-forming elements are incorporated into the wear-resistant protective layer during laser build-up welding. The wear-resistant protective layer preferably comprises an iron-based alloy in which the carbide-forming elements are absorbed and, if necessary, melted.

[0008] Vanadium, niobium, tungsten, titanium and / or chromium are preferably present as carbide-forming elements. During solidification, the carbide-forming elements react with the carbon atoms of the base alloy to form finely distributed metal carbides in the wear-resistant protective layer, which increases the layer hardness and thus the wear resistance of the wear-resistant protective layer.

[0009] Furthermore, it is preferably provided that the carbon content in the wear protection layer increases linearly or degressively from the substrate to the friction contact surface. A linear increase has a particularly positive effect on the crack resistance of the wear protection layer. A degressive increase in carbon concentration is characterized by a decreasing carbon concentration gradient starting from the substrate toward the coating surface. This degressive increase combines increased crack resistance with the ability to maintain the friction coefficient of the wear protection layer for as long as possible during braking.

[0010] It is particularly preferred to construct the wear-resistant protective layer in multiple layers, in particular three layers, wherein the hardness increases with each additional layer. In this case, a gradual increase in hardness or a gradual hardness curve of the wear-resistant protective layer from the substrate to the friction contact surface is thus ensured. The wear-resistant protective layer can, in principle, have at least two layers, preferably three or more layers, which together form the wear-resistant protective layer on the substrate, wherein the layers are stacked one above the other parallel to the substrate.

[0011] Particularly preferably, the carbon content of the first wear protection layer arranged on the base body is less than 0.2 weight percent, in particular less than 0.1 weight percent. Thus, the first layer primarily serves as a ductile buffer layer and contains no or only low carbide content and a low carbon content.

[0012] A second layer is preferably arranged on the first layer, having a higher carbon content than the first layer, with the carbon content being between 0.2 weight percent and 1.5 weight percent, in particular between 0.1 weight percent and 1.0 weight percent. The second layer represents a transition region to the third layer, which is located on the side of the second layer facing away from the first layer. The inclusion of the transition layer not only improves the adhesion between the first and third layers but also reduces thermomechanical stresses in the layer system of the wear protection layer during braking.

[0013] Preferably, as described above, the third layer located or arranged on the side of the second layer facing away from the first layer has the highest carbon content of the layers, in particular a carbon content greater than 1.0 weight percent. Therefore, the third layer serves as the actual wear protection layer with the highest layer hardness and wear resistance.

[0014] The ratio of carbon content to carbide-forming elements is preferably selected such that the carbon atoms are completely or almost completely incorporated in the carbide. The content of carbide-forming metal atoms is preferably similar to the carbon content in the coating, since, in addition to carbon, carbide-forming metal atoms such as vanadium, titanium, niobium or chromium are also required to form metal carbides.

[0015] Furthermore, it is preferably provided that the carbide-forming elements present have a higher affinity for carbon than chromium. This ensures that, in the case of an optional additional alloying of chromium which contributes to increasing the corrosion resistance of the wear protective layer, chromium does not act as a carbide former and can therefore be used to protect the wear protective layer 5 from corrosion.

[0016] The friction brake according to the invention is characterized by the design according to the invention of the friction brake body. This results in the aforementioned advantages.

[0017] The method according to the invention is characterized in that the wear-resistant protective layer is produced with a hardness that increases gradually or continuously from the substrate to the friction contact surface. To this end, the proportion of carbide-forming elements and carbon increases in particular from the substrate to the friction contact surface. In particular, vanadium, titanium, niobium, and / or chromium are used as carbide-forming elements, with the carbon content preferably increasing linearly or decreasingly from the substrate to the friction contact surface. In particular, the wear-resistant protective layer is produced in multiple layers, in particular three layers, with its hardness increasing with each additional layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Further advantages and preferred features and feature combinations are particularly apparent from the preceding description. In the following, the invention will be explained in more detail with reference to the accompanying drawings.

[0019] Figure 1 An advantageous friction brake body is shown in a perspective view, and

[0020] Figure 2 A schematic sectional view of a friction brake body is shown in order to explain an advantageous design and an advantageous production method of the friction brake body. DETAILED DESCRIPTION

[0021] Figure 1 In a simplified perspective view, a friction brake body of a friction brake 2 (not shown in greater detail here) of a motor vehicle is shown, which is designed as a brake disk 1. The brake disk 1 is of circular design and serves to cooperate with a movable brake pad of the friction brake, which can press against at least one of the end faces of the brake disk 1. The brake disk groove, which is optionally present, is located in the Figure 1 Not shown.

[0022] The brake disk 1 has a base body 3 of circular design and, on its end sides, each having a friction contact surface 4 formed by a wear-resistant protective layer 5 on the base body 3. The base body 3 is preferably made of gray cast iron, and the wear-resistant protective layer 5 extends at least over the friction contact region of the respective end side of the base body 3. The wear-resistant protective layer is produced on the base body 3, for example, by a laser build-up welding process.

[0023] The wear protection layer 5 is characterized in that it has an increasing hardness from the base body 3 to the free friction contact surface 4. In particular, the wear protection layer has a stepped or continuous hardness profile in the axial direction or in the direction from the base body 3 to the friction contact surface 4. Figure 1In the exemplary embodiment, the wear protection layer 5 is multi-layered, i.e., bi-layered. Thus, the wear protection layer 5 is formed from two layers 5_1 and 5_2, wherein the outer layer 5_1 has a higher hardness than the layer 5_2 located between the layer 5_1 and the base body 3. The different hardnesses of the two layers 5_1 and 5_2 are particularly due to the different proportions of carbide-forming elements and carbon. By increasing the hardness of the wear protection layer from the base body 3 to the layer surface at the friction contact surface 4, the crack resistance of the brake disc 1 is improved. In particular, the advantageous design ensures that crack propagation into the base body 3 is avoided. This is achieved by a graded distribution of carbon and carbide-forming elements, such as vanadium, titanium, niobium, or chromium, within the wear protection layer 5. During solidification, the reaction of the carbide-forming elements with carbon atoms results in the formation of finely distributed metal carbides in the wear protection layer 5. This increases the hardness of the respective layers 5_1 and 5_2 and, therefore, the wear resistance of the wear protection layer 5. The content of carbon and carbide-forming elements increases in the direction of the friction contact surface 4, wherein the carbon and carbide-forming elements increase in the direction of the friction contact surface 4 according to Figure 1 In this embodiment, the hardness of the wear-resistant protective layer 5 or the content of carbon and carbide-forming elements increases continuously from the substrate 3 to the friction contact surface 4 .

[0024] In particular, the wear-resistant protective layer 5 comprises an iron-based alloy whose carbon content tends to increase within the wear-resistant protective layer 5 starting from the base body toward the friction contact surface 4. This can be achieved, for example, by varying the coating material. The carbon content preferably increases at least substantially linearly or degressively, wherein a linear increase improves crack resistance and a degressive increase ensures that the coefficient of friction on the friction contact surface 4 is maintained as long as possible.

[0025] Figure 2 Another embodiment of a brake disc 1 is shown, wherein Figure 2 A longitudinal section through a cutout of a brake disc 1 is shown. Unlike the previous embodiment, the wear protection layer 5 is now constructed as a three-layer structure, with the third layer 5_3 located between the base body 3 and the previous layer 5_2. The carbon content varies from layer to layer to ensure a stepwise increase in the direction of the friction contact surface 4.

[0026] The first layer 5_3 on the base body 3 serves here primarily as a ductile buffer layer with no or only a small proportion of carbides and therefore has only a low carbon content of preferably less than 0.1 wt. %.

[0027] The second layer 5_2 represents the transition region to the outer layer 5_1, which forms the friction contact surface 4. Layer 5_2 not only improves the adhesion between layer 5_1 and layer 5_3, but also reduces the thermomechanical stresses in the layer system during braking with the brake disc 1. Layer 5_2 has a higher carbon content than the first layer 5_3, preferably between 0.1 weight percent and 1.0 weight percent.

[0028] The third layer 5_1 acts as the actual wear protection layer and thus forms the friction contact surface 4. The third layer 5_1 is characterized by the highest carbon content and thus the highest layer hardness. Therefore, the carbon content of the layer 5_1 is preferably greater than 1.0 weight percent.

[0029] Since, in addition to carbon, carbide-forming elements such as vanadium, titanium, niobium, or chromium also contribute to the formation of metal carbides, the content of carbide-forming elements is preferably distributed or varied in layers 5_1 to 5_3 in a manner similar to the carbon content, as described above. The ratio of carbon content to carbide-forming metal atoms is preferably selected such that the carbon atoms in the carbides are fully incorporated in the respective layers 5_1 to 5_3. Furthermore, it is preferred that the alloyed carbide-forming metal atoms have a higher affinity for carbon than chromium. This ensures that, despite the additional alloying of chromium, which contributes to improving the corrosion resistance of the wear-resistant protective layer, chromium does not act as a carbide former and can therefore be used to provide corrosion protection for the wear-resistant protective layer 5.

Claims

1. A friction brake body for a friction brake of a motor vehicle (2), wherein: The friction brake body comprises a base body (3), the base body comprising at least one wear-resistant protective layer (5) on at least one friction contact area of ​​the base body (3), wherein the wear-resistant protective layer (5) forms a friction contact surface (4) on a side thereof facing away from the base body (3), wherein the hardness of the wear-resistant protective layer (5) increases stepwise from the base body (3) to the friction contact surface (4), Characterized in that the wear protection layer (5) is constructed in three layers, wherein the hardness increases from layer (5_1-5_3) to layer (5_1-5_3), wherein the first layer (5_3) arranged on the substrate (3) has a carbon content of less than 0.2 weight percent, wherein the second layer (5_2) arranged on the first layer (5_3) has a higher carbon content than the first layer (5_3), i.e. a carbon content of between 0.1 weight percent and 1.0 weight percent, and wherein a third layer (5_1) is arranged on the side of the second layer (5_2) facing away from the first layer (5_3), which has the highest carbon content of the layers (5_1-5_3), i.e. greater than 1.0 weight percent.

2. The friction brake body according to claim 1, characterized in that The wear protection layer (5) has a content of carbide-forming elements and carbon which increases from the base body (3) to the friction contact surface (4).

3. The friction brake body according to claim 1 or 2, characterized in that: Vanadium, niobium, tungsten, titanium and / or chromium are present as carbide-forming elements.

4. The friction brake body according to claim 1 or 2, characterized in that: The ratio of carbon content to carbide-forming elements is selected such that the carbon atoms are completely or almost completely incorporated in the carbide.

5. The friction brake body according to claim 1 or 2, characterized in that: In the case of additional alloying with chromium, the other carbide-forming elements present have a higher affinity for carbon than chromium.

6. The friction brake body according to claim 1, characterized in that The friction brake body is a brake disc (1).

7. The friction brake body according to claim 1, characterized in that The first layer (5_3) arranged on the substrate (3) has a carbon content of less than 0.1 weight percent.

8. A friction brake (2) for a motor vehicle, comprising at least one friction brake body and at least one movable brake pad assigned to the friction brake body, characterized in that The construction of a friction brake body according to any one of claims 1 to 7.

9. Method for producing a friction brake body for a friction brake (2) for a motor vehicle according to any one of claims 1 to 7, wherein: A friction brake body is manufactured from a base body (3) having at least one wear-resistant protective layer (5) in at least one friction contact area of ​​the base body (3) such that the wear-resistant protective layer (5) forms a friction contact surface (4) on its side facing away from the base body (3), wherein the wear-resistant protective layer (5) is manufactured with a hardness that increases gradually from the base body (3) to the friction contact surface (4). Characterized in that the wear-resistant protective layer (5) is constructed in three layers, wherein the hardness increases from layer (5_1-5_3) to layer (5_1-5_3), wherein the first layer (5_3) arranged on the substrate (3) has a carbon content of less than 0.2 weight percent, wherein the second layer (5_2) arranged on the first layer (5_3) has a higher carbon content than the first layer (5_3), i.e. a carbon content between 0.1 weight percent and 1.0 weight percent, and wherein a third layer (5_1) is arranged on the side of the second layer (5_2) facing away from the first layer (5_3), which has the highest carbon content of the layers (5_1-5_3), i.e. greater than 1.0 weight percent.

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