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

Description

[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 has a base body with at least one wear protection layer on at least one friction contact region of the base body, wherein the wear protection 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, with at least one friction brake body which is designed as described above, with at least one brake pad which is assigned to the friction brake body and is arranged to be displaceable.

[0003] Furthermore, the invention relates to a method for producing the friction brake body described above. State of the art

[0004] Friction brake bodies for motor vehicles, in particular brake discs for friction brakes, are already known from the prior art. When used as intended, the friction brake body, in particular the brake disc, is connected in a rotationally fixed manner to a wheel of a motor vehicle and arranged opposite a movable brake block. When the brake block is pressed against the friction brake body, friction is generated between the friction brake body and the brake block, which reduces the wheel speed and thus brakes the wheel. To reduce wear caused by the friction that occurs, it is also known to apply a wear protection layer at least in the friction contact area of ​​the base body, which interacts with the brake block. The wear protection layer reduces wear during braking and thus extends the service life of the friction brake body itself and the friction brake as a whole.

[0005] A coated brake disc is already known from published patent application EP 3 034 902 A1, in which a wear-resistant layer with embedded ceramic particles is produced by laser deposition welding. Furthermore, published patent application DE 10 2010 048 075 A1 already discloses a brake disc with a base body made of a graphite-containing metallic material and with a wear-resistant layer on its friction surfaces, wherein a surface layer of the friction surfaces adjacent to the wear-resistant layer does not contain any graphite.

[0006] DE 10 2019 212 844 A1 can also be cited as a prior art document. Disclosure of the invention

[0007] The friction brake body according to the invention with the features of claim 1 has the advantage that the crack resistance of the friction brake body is advantageously increased. According to the invention, this is achieved by the hardness of the wear protection layer increasing gradually from the base body to the frictional contact surface. This increases the crack resistance of the coating from the frictional contact surface to 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 at the frictional contact surface, and at the same time, sufficient ductility and crack resistance to prevent a crack forming on the frictional contact surface from propagating into the base body.As a result, the friction brake body can also be subjected to thermomechanical stresses, such as those that can occur during emergency braking, without a crack forming in the base body or propagating into the base body, thereby increasing the overall mechanical strength and robustness, including corrosion resistance. Crack growth, if a crack occurs, therefore preferentially occurs along the hard materials in the friction brake body according to the invention, since these inclusions reduce the fracture toughness of the wear-resistant layer. However, according to the invention, they occur more strongly in the area of ​​the friction contact surface than in the area of ​​the base body.

[0008] According to a preferred embodiment of the invention, the wear protection layer has a proportion of carbide-forming elements and carbon that increases from the base body to the frictional contact surface. This ensures that the hardness of the wear protection layer increases toward the frictional contact surface, as described above. The carbide-forming elements are introduced into the wear protection layer, particularly during laser deposition welding. The wear protection layer preferably comprises an iron-based alloy in which the carbide-forming elements are incorporated and, if necessary, melted.

[0009] Vanadium, niobium, titanium, and / or chromium are preferably present as carbide-forming elements. During solidification, the carbide-forming elements react with carbon atoms of the base alloy to form finely distributed metal carbides in the wear-resistant layer, increasing the layer's hardness and thus its wear resistance.

[0010] Furthermore, it is preferably provided that the carbon content in the wear-protection layer increases linearly or degressively from the base substrate to the friction contact surface. The linear increase has a particularly positive effect on the crack resistance of the wear-protection layer. The degressive increase in carbon concentration is characterized by the carbon concentration gradient decreasing from the substrate toward the coating surface. The degressive increase combines the increased crack resistance with the longest possible maintenance of the friction coefficient of the wear-protection layer during braking.

[0011] According to the invention, the wear protection layer is formed in three layers, with the hardness increasing from layer to layer. In this case, a gradual increase in hardness or a gradual hardness progression of the wear protection layer is ensured, starting from the base body to the frictional contact surface. The wear protection layer can generally have at least two, preferably three, or even more than three layers, which together form the wear protection layer on the base body, with the layers lying one above the other in layers parallel to the base body.

[0012] According to the invention, the first layer of the wear-resistant coating arranged on the base body has a carbon content of less than 0.2 wt.%, in particular less than 0.1 wt.%. Thus, the first layer primarily serves as a ductile buffer layer with no or only a low carbide content and a low carbon content.

[0013] According to the invention, a second layer is arranged on the first layer, the carbon content of which is higher than that of the first layer, the carbon content being between 0.2 wt.% and 1.5 wt.%, in particular between 0.1 wt.% and 1.0 wt.%. The second layer represents a transition region to the third layer, which lies on the side of the second layer facing away from the first layer. The introduction of the transition layer not only improves the adhesion between the first and third layers, but also reduces the thermomechanical stresses in the layer system of the wear protection layer during braking.

[0014] According to the invention, the third layer, which, as already mentioned above, lies or is 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 of more than 1.0 wt.%. Thus, the third layer functions as the actual wear protection layer with the highest layer hardness and wear resistance.

[0015] Preferably, the ratio of carbon content to carbide-forming elements is selected such that the carbon atoms are completely or almost completely bound in the carbides. The content of carbide-forming metal atoms is preferably formed analogously to the carbon content in the coating, because the formation of metal carbides requires not only carbon but also carbide-forming metal atoms such as vanadium, titanium, niobium, or chromium.

[0016] Furthermore, it is preferred 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 is advantageous for increasing the corrosion resistance of the wear-resistant layer, chromium does not act as a carbide former and is thus available for the corrosion protection of the wear-resistant layer.

[0017] The friction brake according to the invention with the features of claim 6 is characterized by the inventive design of the friction brake body. This results in the advantages already mentioned.

[0018] The inventive method with the features of claim 7 is characterized in that the wear protection layer is produced with a hardness that gradually increases from the base body to the frictional contact surface. To this end, in particular, the proportion of carbide-forming elements and carbon is increased from the base body to the frictional contact surface. Vanadium, titanium, niobium, and / or chromium are used in particular as carbide-forming elements, with the carbon content preferably increasing linearly or degressively from the base substrate to the frictional contact surface. According to the invention, the wear protection layer is produced in multiple layers, in particular three layers, with an increasing degree of hardness from layer to layer.

[0019] Further advantages and preferred features and combinations of features emerge in particular from the above description and from the claims. The invention will be explained in more detail below with reference to the drawings. Figure 1 shows an advantageous friction brake body in a perspective view, and Figure 2 shows a schematic sectional view of the friction brake body to explain the advantageous structure of the friction brake body and an advantageous manufacturing method.

[0020] Figure 1shows a simplified perspective view of a friction brake body designed as a brake disc 1 of a friction brake 2 of a motor vehicle (not shown in detail here). The brake disc 1 is circular in shape and serves to interact with a displaceable brake pad of the friction brake, which can be pressed against at least one of the end faces of the brake disc 1. An optionally available brake disc chamber is shown in Figure 1 not shown.

[0021] The brake disc 1 has a base body 3, which is circular in shape and has a frictional contact surface 4 on each of its end faces, which is formed by a wear-protection layer 5 on the base body 3. The base body 3 is preferably made of gray cast iron, and the wear-protection layer 5 extends at least over a frictional contact area of ​​the respective end face of the base body 3. The wear-protection layer is produced on the base body 3, for example, by a laser deposition welding process.

[0022] The wear protection layer 5 is characterized in that it has an increasing hardness starting from the base body 3 up to the free friction contact surface 4. In particular, the wear protection layer has a stepwise or continuous hardness progression axially or in the direction from the base body 3 to the friction contact surface 4. According to the embodiment of Figure 1the wear protection layer 5 is multi-layered, namely two-layered, so that 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. In particular, the different degrees of hardness of the two layers 5_1, 5_2 are ensured by different proportions of carbide-forming elements and carbon. By increasing the hardness of the wear protection layer, starting from the base body 3 up to the layer surface at the friction contact surface 4, the brake disc 1 is improved in its crack resistance. In particular, this advantageous design ensures that crack propagation into the base body 3 is prevented.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 forms finely distributed metal carbides in the wear protection layer 5, which increase the layer hardness of the respective layer 5_1, 5_2 and thus the wear resistance of the wear protection layer 5. The content of carbon and carbide-forming elements increases in the direction of the frictional contact surface 4, whereby according to the present embodiment of . Figure 1 increases stepwise from layer 5_2 to layer 5_1. According to an alternative embodiment, the hardness of the wear protection layer 5, or the content of carbon and carbide-forming elements, increases continuously from the base body 3 to the frictional contact surface 4.

[0023] The wear-resistant layer 5 comprises, in particular, an iron-based alloy whose carbon content within the wear-resistant layer 5 tends to increase from the base body up to the frictional contact surface 4. This is achieved, for example, by varying the coating material. The carbon content preferably increases at least substantially linearly or degressively, with a linear increase improving crack resistance and a degressive increase ensuring the friction coefficient at the frictional contact surface 4 is maintained for as long as possible.

[0024] Figure 2 shows a further embodiment of the brake disc 1, wherein Figure 2a longitudinal sectional view of a section of the brake disc 1. In contrast to the previous embodiment, the wear protection layer 5 is now formed in three layers, with a third layer 5_3 being present between the base body 3 and the previous layer 5_2. The carbon content varies from layer to layer to ensure a gradual increase toward the frictional contact surface 4.

[0025] The first layer 5_3 on the base body 3 serves primarily as a ductile buffer layer with no or only a small carbide content and therefore also has only a low carbon content of preferably less than 0.1 wt.%.

[0026] The second layer 5_2 represents a transition area to the outer layer 5_1, which forms the friction contact surface 4. Layer 5_2 not only improves the adhesion between layers 5_1 and 5_3, but also reduces 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 wt.% and 1.0 wt.%.

[0027] The third layer 5_1 functions as the actual wear protection layer and therefore forms the friction contact surface 4. The third layer 5_1 is characterized by the highest carbon content and thus the highest layer hardness. The carbon content of layer 5_1 is therefore preferably higher than 1.0 wt.%.

[0028] Since, as already mentioned above, carbide-forming elements such as vanadium, titanium, niobium or chromium are used in addition to carbon to form metal carbides, the content of the carbide-forming elements is preferably distributed or varied analogously to the carbon content in layers 5_1 to 5_3. The ratio of the carbon content to the carbide-forming metal atoms is preferably selected such that the carbon atoms are completely bonded into carbides in the respective layer 5_1 to 5_3. Furthermore, it is preferred that the added carbide-forming metal atoms have a higher affinity for carbon than chromium. This ensures that in the case of additional alloying of chromium, which is advantageous for increasing the corrosion resistance of the wear protection layer, chromium does not function as a carbide former and is thus available for corrosion protection of the wear protection layer 5.

Claims

1. Friction brake member, in particular brake disc (1), for a friction brake (2) of a motor vehicle, wherein the friction brake member comprises a base member (3) having at least one wear protection layer (5) on at least one frictional contact area of the base member (3), wherein the wear protection layer (5) forms a frictional contact surface (4) on its side facing away from the base member (3), wherein the hardness of the wear protection layer (5) increases stepwise from the base member (3) up to the frictional contact surface (4), characterised in that the wear protection layer (5) is formed in three layers, wherein the hardness increases from layer (5_1-5_3) to layer (5_1-5_3), wherein a first layer (5_3) arranged on the base member (3) comprises a carbon content of less than 0.2 % by weight, in particular less than 0.1 % by weight, wherein a second layer (5_2) arranged on the first layer (5_3) comprises a higher carbon content than the first layer (5_3), in particular a carbon content between 0.1 % by weight and 1.0 % by weight, 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 comprises the highest carbon content of the layers (5_1-5_3), in particular greater than 1.0 % by weight.

2. Friction brake member according to claim 1, characterised in that the wear protection layer (5) comprises a proportion of carbide-forming elements and carbon which increases from the base member (3) to the frictional contact surface (4).

3. Friction brake member according to one of the preceding claims, characterised in that vanadium, niobium, tungsten, titanium and / or chromium are present as carbide-forming elements.

4. Friction brake member according to one of the preceding claims, characterised in that the ratio of carbon content and carbide-forming elements is selected in such a way that the carbon atoms are completely or almost completely bound in the carbides.

5. Friction brake member according to one of the preceding claims, characterised in that other carbide-forming elements present comprise a higher carbon affinity than chromium, in the case of an additional alloying of chromium.

6. Friction brake (2) for a motor vehicle, with at least one friction brake member and with at least one displaceable brake pad assigned to the friction brake member, characterised by the design of the friction brake member, in particular as a brake disc (1) according to one of claims 1 to 5.

7. Method for manufacturing a friction brake member, in particular according to one of claims 1 to 5, for a friction brake (2) of a motor vehicle, wherein the friction brake member is manufactured from a base member (3) with at least one wear protection layer (5) on at least one frictional contact area of the base member (3) in such a way that the wear protection layer (5) forms a frictional contact surface (4) on its side facing away from the base member (3), wherein the wear protection layer (5) is manufactured with a hardness which increases stepwise from the base member (3) up to the frictional contact surface (4), characterised in that the wear protection layer is manufactured in three layers, with an increasing degree of hardness from layer to layer, wherein a first layer (5_3) arranged on the base member (3) comprises a carbon content of less than 0.2 % by weight, in particular less than 0.1 % by weight, wherein a second layer (5_2) arranged on the first layer (5_3) comprises a higher carbon content than the first layer (5_3), in particular a carbon content between 0.1 % by weight and 1.0 % by weight, 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 comprises the highest carbon content of the layers (5_1-5_3), in particular greater than 1.0 % by weight.