EP3155284A1

EP3155284A1 - Brake disc for a motor vehicle

Info

Publication number: EP3155284A1
Application number: EP15724523.4A
Authority: EP
Inventors: Oliver Lembach
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2014-06-14
Filing date: 2015-05-23
Publication date: 2017-04-19
Also published as: JP2017523353A; US20170122392A1; CN106415048A; DE102014008844A1; WO2015188918A1

Abstract

The invention relates to a brake disc (1) for a motor vehicle comprising a substrate (2), in particular a grey cast substrate, at least one friction surface (8) formed on the substrate (2) and at least one cover layer which is applied to the at least one friction surface (8). Said cover layer is harder and thinner than the substrate (2), and colour changes (9) are introduced into the cover layer by means of a pulsed laser for identification purposes.

Description

Brake disc for a motor vehicle

The invention relates to a brake disk for a motor vehicle comprising a substrate, in particular a cast iron substrate, at least one friction surface formed on the substrate and at least one cover layer applied at least on the at least one friction surface. Furthermore, the invention relates to a method for producing such a brake disc.

Brake discs have friction surfaces, which form a tribological system with the brake pads. When braking, when the stationary pads are brought into contact with the rotating friction surfaces, the friction surfaces of the brake discs heat up due to friction. The braking effect depends on the condition and the surface condition of the friction surface. The brake disc temperature, which is increased as a result of the braking processes, possibly in conjunction with corrosive media such as water and road salt, leads to or accelerates corrosion occurring on the friction surfaces. For this reason, brake discs are often at the friction surfaces with a

Provided corrosion protection layer. However, due to different coefficients of thermal expansion, for example, this causes cracks which extend to the end of the period

Brake disc main body extend, or cover layer and body different electrochemical voltage potentials, it can lead to corrosion of the body under the cover layer (corrosive infiltration), which leads to a delamination of the coated body and thus to restrictions to the loss of braking effect.

In order to improve the resistance of the brake discs against corrosion and oxidation, especially at elevated temperature, the friction surfaces of

Brake discs made of iron-based material provided with a corrosion protection layer by undergoing a nitrocarburizing surface treatment and subsequent oxidative aftertreatment.

At the same time it is desirable for functional or optical reasons

Recesses, such as holes (perforated brake disc) or slots to introduce into the friction surfaces. Such recesses, however, would be the top layer pierced, which can again come to the corrosion of the body. Even if the cover layer were applied after the introduction of the recesses, there would be an increased risk of corrosion at the edges around the recesses.

From DE 10 2007 027 933 B4 a method for nitrocarburizing brake rotors of a motor vehicle is known. The brake rotor made of an iron-based material is heated and treated in a tempered ferritic nitrocarburizing salt bath and a tempered oxidizing salt bath. After that, the surface of the

Brake rotor on a connection layer and an underlying diffusion layer. Is located at the surface of the compound layer has a Fe ₃ 0 ₄ containing oxide layer before, including, the connection layer primarily of ε-iron nitride, Fe ₃ N, and a minor proportion γ'-iron nitride, Fe N. The diffusion layer contains the iron-based material has a concentration diffused nitrogen which is lower than in the tie layer.

DE 10 201 1 053 253 A1 describes a brake disk made of carrier part and friction ring, which are connected to one another via connecting elements made of steel material. In this case, the connecting elements at least at the end portions on a corrosion protection layer, which consists of a corresponding diffusion layer, an overlying Eisencarbonitride compound layer and an oxide layer lying thereon.

DE 195 25 182 A1 discloses a gas process for the production of corrosion and wear protection layers on iron-based materials, which has the disadvantages of

Salt bath process in terms of environmental impact and generated

Surface topography - the surfaces produced in the salt bath process are rough and require post-processing - avoids. First, the nitrocarburization is carried out in a normal pressure gas process, wherein the compound layer of iron carbonitrides is formed, whereupon in a plasma-assisted vacuum method, the surface of the connecting layer is activated before by oxidation in the normal pressure gas process, a closed and uniform oxide layer is formed.

The described method for producing a corrosion and

Wear-resistant coating on low-alloy steels is known under the name IONIT OX ™ from Sulzer Metco, Bergisch Gladbach (http://www.sulzer.com). EP 2 394 072 B1 describes a method for producing a cast iron brake disk for a vehicle, the friction surfaces of which are produced by means of carburizing, carbonitriding, case hardening, gas nitriding, oxide nitriding, gas nitrocarburizing, plasma nitriding,

Be treated by plasma oxidation, boriding, plasma carburizing or Plasmaborieren. The friction surfaces can be provided with a coating of tungsten carbide, chromium carbide and nickel or of tungsten carbide, cobalt, chromium and nickel before the after-treatment.

Also from DE 10 201 1 122 308 A1 a coated component or brake disc is known, wherein between the substrate and cover layer by an intermediate layer

Phosphating, nitriding, boriding, sputtering, bainitriding, carburizing, carbonitriding, plasmanitrocarburizing, anodizing, by a chemical nickel dispersion, by a thermal process, by a chemical process, by physical

Gas phase deposition and / or formed by chemical vapor deposition.

DE 10 2004 016 092 A1 discloses a brake disk with a main body and a coating with at least one wear-resistant layer serving as a friction layer. The layer thickness of at least one layer of the coating and / or the

Layer thickness of the coating is a maximum of about 150 pm.

From DE 10 2012 221 365 A1 a method is known to provide a brake disk with a marking on the friction surfaces of the brake disk. In order to achieve an abrasion-resistant marking, a chemical or physical treatment of the brake disc is performed by a template in the form of marking. Thus, the brake disc has an area in the form of the marking, the other properties, such as a different hardness, than the rest of the

Brake disc.

From DE 698 11 661 T2 discloses a brake disc with radial grooves on the friction surfaces, which are circular arc-shaped and to an outside, in the radial direction, the brake disc are open known.

DE 10 201 1075 821 A1 discloses a brake disk with a base body and a wear layer applied thereto. To realize the bond between the wear layer and the base body, the contact surface of the base body is pretreated by laser radiation to modify the surface topography, DE 10 2010 013 343 A1 describes a friction disk with a wear protection layer and an integrated wear indicator. Between the

Wear protection layer and the friction disc is at least one

Indicating surface provided, which occupies a part of the friction surface and differs by at least one of the features coloring and structure of the friction surface and the wear protection layer. The indication surface element is set free by removing the wear protection layer.

The present invention has for its object to provide a brake disc with optical markings, which is still protected against corrosion and wear.

This object is achieved by the objects of the independent

Claims solved. Advantageous embodiments are the subject of the dependent claims.

The invention is based on the general idea, instead of recesses which penetrate the brake disc, to introduce optical markings in the cover layer. This preserves the anticorrosion effect of the cover layer. Suitably, the cover layer is harder and thinner than the substrate, color changes being incorporated in the cover layer. It is therefore essential that the substrate is still covered by the cover layer where the color changes are located. In this case, the cover layer is preferably a wear protection layer or

Corrosion protection layer and the substrate a brake disc body made of gray cast iron. It can color changes are introduced to allow identification, for example, with a brand, type number or serial number, the brake disc.

A cheap option is that the color changes and

optionally depressions by means of a pulsed laser in the cover layer

are introduced. With a pulsed laser very precise material processing can be made, so that it is possible to introduce the color changes and possibly depressions only within the cover layer. By the energy of the pulsed laser, for example, chemical reactions or

Remelting processes are triggered which result in a color change, for example in a darkening, brightening or metallic luster. Another favorable possibility provides that the top layer has a microhardness of greater than 300 HV.03, more preferably greater than 500 HV.03 or most preferably greater than 800 HV.03. Due to the high hardness of the cover layer, the wear of the cover layer is reduced, so that the service life is increased.

A particularly favorable possibility provides that the cover layer ceramic,

For example, carbon fiber reinforced silicon carbide (C / SiC) and / or a silicon carbide particle reinforced aluminum alloy (Al-SiC). Through the use of ceramic in the top layer, a high hardness of the top layer is achieved, which in turn extends the life of the brake disc.

Another particularly favorable possibility provides that the top layer a

Layer thickness below 1000 pm, in particular has a layer thickness between 100 and 500 pm. By a small layer thickness of the cover layer, the cost of the cover layer can be reduced. In addition, the mechanical

Characteristics of the brake disc thereby more influenced by the substrate, which is cheaper and offers high mechanical stability.

An advantageous solution provides that between the substrate and the cover layer at least one surface layer is formed, the nitride, carbide, and / or oxide-containing layers comprise, that are formed by nitriding, carburizing, nitrocarburizing and / or oxidizing. To improve corrosion and crack resistance as well as wear protection, the cover layer consists of a cermet material of a metallic matrix and a ceramic component distributed therein, which constitutes 30 to 70% by weight of the cermet material.

"Cermet" refers to very hard and wear-resistant composites of ceramic materials in a metallic matrix with high thermal shock and

Oxidation resistance.

The cermet topcoat in conjunction with nitriding, carburizing,

Nitrocarburizing and / or oxidizing hardened surface layer formed as an electrochemical barrier gives the component significantly improved corrosion and crack resistance. As a result, corrosive infiltration with the consequence of total failure of the layer system by delamination significantly delayed and thus the life and longevity of the layer system or the component - such as Brake disc in the vehicle - significantly extended.

A further advantageous solution provides that the metallic matrix is a high-alloyed CrNiMo steel, which preferably has a composition comprising 28% by weight chromium, 16% by weight nickel, 4.5% by weight molybdenum, 1.5% by weight % Silicon, 1.75% carbon by weight, balance iron.

A particularly advantageous solution provides that the metallic matrix is a NiCrMo alloy which preferably has a composition comprising 20 to 23% by weight of chromium, up to 5% by weight of iron, 8 to 10% by weight of molybdenum, 3 , 15 to 4.15 wt .-% of niobium and tantalum in sum, balance nickel, particularly preferably a composition comprising 21, 5 wt .-% chromium, 2.5 wt .-% iron, 9.0 wt .-% molybdenum , 3.7 wt .-% of niobium and tantalum in sum, balance nickel.

Another particularly advantageous solution provides that the ceramic component comprises oxide ceramics selected from Al ₂ O ₃ , Ti0 ₂ , Zr0 ₂ and MgAl ₂ 0 ₄ and combinations thereof.

An advantageous possibility provides that the ceramic component Al ₂ 0 ₃ and at least one further oxide ceramic comprises, selected from the group comprising Ti0 ₂ , Zr0 ₂ , MgAI ₂ 0 ₄ , wherein Al ₂ 0 _3, a proportion of 60 to 90 wt. -% of the total

Ceramic component.

A further advantageous possibility provides that the surface layer starting from the substrate has a diffusion layer, a nitride- and carbide-containing bonding layer and an oxide layer, wherein the diffusion layer has a layer thickness of 0.1 to 0.8 mm, the bonding layer has a layer thickness of 2 to 30 μιη and the oxide layer has a layer thickness of 1 to 5 pm.

Preferably, the tie layer contains predominantly ε-iron nitride, as well as other nitrides and carbides. The oxide layer preferably contains predominantly iron oxide.

A particularly advantageous possibility provides that between the cover layer and the surface layer, an intermediate layer is provided, which consists of a nickel-based alloy, preferably a nickel chromium alloy, or of the metallic matrix consisting of the nickel-based alloy or the intermediate layer

Matrix metal has a layer thickness of 30 to 120 pm.

In order to improve the bonding of the cover layer to the substrate, the surface of the substrate and thus the surface or intermediate layers in the through

Cover layer covered areas mechanically roughened or profiled, so that the cover layer interlocks with the substrate.

Furthermore, the above-mentioned object is achieved according to the invention by a method for producing a brake disk as described above,

which comprises producing a brake disk blank, forming the cover layer, at least on the friction surfaces of the brake disk, and introducing the color changes into the cover layer by means of a pulsed laser.

In this way you get a brake disc, with a corrosion and

wear-protective cover layer.

A favorable solution envisages nitriding, carburizing, nitrocarburizing in a gas, plasma or salt bath process and / or oxidizing, preferably nitrocarburizing, plasma activating and oxidizing, the substrate, at least at the friction surfaces, thereby forming, by anodic or plasma oxidation of the

Surface layer, providing a cermet material of a metallic matrix and a distributed therein ceramic component, which constitutes 30 to 70 wt .-% of the cermet material before, and thereon before the forming of the cover layer by applying the cermet material on the surface layer.

The application of the cermet material can be carried out by thermal spraying.

A particularly favorable solution provides before the nitriding, carburizing, nitrocarburizing and / or oxidizing that the surfaces of the substrate, at least to the

Friction surfaces, mechanically roughened or profiled.

Alternatively or in addition to the profiling of the substrate surface can after the

Nitriding, carburizing, nitrocarburizing and / or oxidizing the substrate surface, a nickel-based alloy or the pure matrix metal are applied to the surface layer and so an additional intermediate layer as wear protection and optionally be formed to assist the adhesion of the cover layer to the surface layer.

The nickel-based alloy or the matrix metal can also be applied by thermal spraying.

Other important features and advantages of the invention will become apparent from the

Subclaims, from the drawings and from the associated description of the figures with reference to the drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Preferred embodiments of the invention are illustrated in the drawings and will be described in more detail in the following description, wherein like reference numerals refer to the same or similar or functionally identical components.

In each case show schematically:

Fig. 1 is a plan view of a brake disc according to the invention with several

recesses

2 is a sectional view of a section of the brake disc, in the region of a depression, along the line AA of Fig. 1,

3 is a sectional view of a section of the brake disc, in the region of a depression, with an alternative form of the depression, along the line AA of Fig. 1,

Fig. 4 is a cross-sectional view through a section of an inventive

Brake disc without recess with hardened surface layer, another nickel-based intermediate layer and cover layer, 5 shows a cross-sectional view through a section of a brake disk according to the invention with the surface layer formed from diffusion layer, connecting layer and oxide layer, a further nickel-based intermediate layer and covering layer, and FIG

6 is a microscopic micrograph of a portion of a brake disc according to the invention with profiled surface and hardened surface layer, another nickel-based

Interlayer and topcoat.

The invention relates to a brake disk 1 with a substrate 2, in particular with a cast iron substrate whose corrosion and wear properties are improved by a hardened surface layer 3 and a cover layer 4 applied thereon, optionally also further layers, wherein color changes 5 and optionally recesses 6, which do not penetrate the cover layer 4, are introduced into the cover layer 4. The layers prevent or reduce z. As the spread of cracks that can occur during operation of the brake disc 1 on the surface. The fact that the crack propagation is avoided in the substrate 2, a corrosive infiltration of the layers is effectively prevented, so that it does not come or only much later for failure of the brake disc 1, for example by delamination. The recesses 6 may be intended for example for cleaning the brake pads or be designed as a wear marker.

A brake disk 1 shown in FIG. 1 has a hub 7 and at least one, for example two, friction surfaces 8, which are arranged coaxially with the hub. Brake pads are applied to the friction surfaces during a braking process. The friction surfaces 8 each have the surface layer 3 and the cover layer 4 applied thereto. In each cover layer several, for example four, recesses 6 are introduced.

In order not to destroy the corrosion protection effect of the cover layer 4, the recesses 6 are introduced only in the cover layer 4, so the cover layer 4 does not penetrate. The residual thickness of the cover layer 4 below the recesses 6 should be large enough to prevent white ^¬ terhin cracking in the top layer. 4

The depressions 6 can be introduced into the cover layer 4 with the aid of a pulsed laser. With the pulsed laser, the cover layer 4 can be processed without exerting large forces on the cover layer 4. As a result, damage to the cover layer 4 can be avoided even with small layer thicknesses of the cover layer 4.

Furthermore, the pulsed laser makes it possible to form the depressions 6 almost as desired. For example, steep edges or smooth transitions between the surface and the recess 6 are possible.

Furthermore, a color change 9 of the surface can also be made possible with the aid of the pulsed laser. For example, serial numbers,

Type numbers or trademarks are applied to the friction surfaces 8 of the brake disc 1. It is also possible to use a recess 6 for the identification of the brake disc 1.

In the following, the embodiment of an exemplary cover layer 4 is explained, in which color changes 9 can be introduced according to the invention.

On the surface of the substrate 2, which forms the main body of the brake disc 1, a hardened surface layer 3 is formed by nitriding, carburizing, nitrocarburizing and / or oxidizing, to which a cover layer 4 is applied. The cover layer 4 consists of a cermet material of a metallic matrix and a ceramic component distributed therein, which constitutes 30 to 70 wt .-% of the cermet material.

An alternative brake disk shown in FIG. 4 has, between the hardened surface layer 3 and the cover layer 4, an additional intermediate layer 10 of a nickel-based alloy, preferably a corrosion-resistant and high-temperature resistant nickel chromium alloy.

The production of a brake disk 1 according to the invention is explained below with reference to FIG. 5, in which the layers of a brake disk 1 according to the invention are sketched in more detail in an embodiment with an additional intermediate layer 10.

A brake disc according to the invention comprises on the substrate 2, which forms a cast brake disc blank 12, the hardened surface layer 3, preferably by nitrocarburizing, plasma activating and oxidizing by the IONIT OX ™ method, but optionally also by other nitrating, carburizing, nitrocarburizing and / or oxidation processes is formed. Optionally, the surface of the substrate 2 may be previously be profiled chanically. Starting from the substrate 2, the surface layer 3 is composed of a diffusion layer 31, a connection layer 32 and an oxide layer 33. During the nitrocarburization nitrogen and carbon penetrate into the surface of the substrate 2, wherein in the connecting layer 32, the layer thickness is in a range of 2 to 30 μιη, predominantly ε-iron nitride or carbonitride and to a lesser extent γ'-iron nitride and Special nitrides are formed. Below the bonding layer 32, the diffusion layer 31 extends into the substrate 2, which has lower concentrations of diffused nitrogen and carbon than in the bonding layer 32, and the nitrogen is in "solution" in the substrate structure besides the special nitrides, carbides, and nitride precipitates 31 is in a range of 0.1 to 0.8 mm, depending on the treatment conditions and the substrate properties.

The surface of the connecting layer 32 is oxidized after plasma activation, so that a substantially closed oxide layer 33 of Fe ₃ 0 ₄ with a layer thickness in the range of 1 to 5 pm is formed on the connecting layer 32, which has a defined pore structure.

In order to obtain the layer structure from FIG. 5, an intermediate layer 10 made of a nickel-based alloy or the matrix metal is applied to the oxide layer 33 before the cermet material is applied to form the cover layer 4. The intermediate layer 10 can have a layer thickness in the range from 30 to 120 μm and the cover layer 4 can have a layer thickness in the range from 100 to 500 μm.

Between the intermediate layer 10 and the oxide layer 33 - in embodiments without intermediate layer 10 corresponding between the cermet cover layer 4 and the oxide layer 33 - there is a mixing zone 1 1, in which the iron oxide of the oxide layer 33 with the nickel-based alloy or the matrix metal of the intermediate layer 10 (or mixed with the matrix metal of the cover layer 4). If the intermediate layer 10 consists of a nickel-based alloy, which differs from the matrix metal, then there is also a mixing zone 11 between the cover layer 4 and the intermediate layer 10. The thickness of the mixing zone 11 may vary depending on the type of application and application parameters.

Both the application of the nickel-based alloy or the matrix metal to form the intermediate layer 10 and the application of the cermet material to form the cover layer 4 can be carried out by thermal spraying. The hardened surface layer 3 is on the surface of the substrate 2 with a layer thickness of about 30 μητι connecting layer 32 and 3 μηι oxide layer 33 before and is indicated by the dashed line , On the profiled substrate 2 and the surface layer 3, a nickel-based intermediate layer 10 is applied in this embodiment, with a layer thickness of about 100 pm average. As can be seen in the photograph, the layer thickness of the intermediate layer 10 varies due to the profiled surface of the substrate 2. The cover layer 4 made of cermet has an average thickness of about 350 μιη. Variations in the layer thickness also result from the profiled surface of the substrate 2, which, however, advantageously provides a better bond between the cover layer 4 and the substrate 2 coated with the intermediate layer 10 due to this toothing effect.

The cover layer 4 and the underlying layers 3, 10 may be limited to tribologically stressed surfaces, that is, to the friction surfaces of the brake disk.

The matrix metal may be a high alloy CrNiMo steel or a NiCrMo alloy. For the additional intermediate layer 10 nickel-based, preferably NiCr alloys, or pure matrix metal without ceramic component in question.

A suitable for forming the metallic matrix of the cover layer 4 CrNiMo steel has the composition Fe 28Cr 16 Ni 4.5 Mo 1, 5 Si 1, 75 C. Suitable NiCrMo alloys include Ni 20-23Cr <5Fe 8-1 OMo 3.15-4.15Nb (+ Ta) compositions (Inconel ™ 625, Special Metals Corporation, Huntington, West Virginia, USA), most preferably Ni 21 , 5Cr 2.5Fe 9.0Mo 3.7 (Nb + Ta).

As a material for forming the intermediate layer 10, other nickel-based alloys, in particular NiCr alloys can also be used.

The ceramic component of the cover layer 4 comprises oxide ceramics such as Al ₂ O ₃ , Ti0 ₂ , Zr0 ₂ and MgAl ₂ 0 ₄ (spinel). These can be selected individually or in combinations as a reinforcing ceramic component of the cermet. For example, in addition to Al ₂ O ₃ as the main component, the ceramic component may have at least one further oxide ceramic as a minor component, which is selected from the group comprising TiO ₂ , ZrO ₂ , MgAl ₂ O ₄ . The proportion of Al ₂ 0 ₃ of the total ceramic component, the proportion in the cermet material in the range of 30 to 70 wt .-% of the cermet material can account for 60 to 90 wt .-%. The further oxide ceramic Ti0 ₂ , Zr0 ₂ and / or MgAl ₂ 0 ₄ is then present in a proportion of 10 to 40 wt .-% of the total ceramic component. Preferably, the proportion of Al ₂ 0 ₃ of the total ceramic component in the range of 75 to 85 wt .-%, preferably 80 wt .-%.

The covering layer 4 of the cermet material, for example applied by thermal spraying, has a porosity of less than 5% and a microhardness of between 300 HV.03 and 1000 HV.03.

Claims

claims

1. brake disk (1) for a motor vehicle comprising a substrate (2), in particular a gray cast substrate, at least one on the substrate (2) formed friction surface (8) and at least one at least on the at least one friction surface (8) applied cover layer ( 4)

characterized in that

- The cover layer (4) is harder and thinner than the substrate (2), and that

- In the cover layer (4) by means of a pulsed laser color changes (9) are introduced to allow an identification.

2. Brake disc (1) according to claim 1,

characterized in that

- The cover layer (4) has a microhardness greater than 300 HV.03 and / or

- The cover layer (4) ceramic, for example C / SiC; Al-SiC, and / or

- The cover layer (4) has a layer thickness below 1000 pm, in particular a layer thickness between 100 and 500 μηι.

3. Brake disc (1) according to one of claims 1 to 2,

characterized in that

- Between the substrate (2) and the at least one cover layer (4) at least one surface layer (3) is formed, which comprises nitride, carbide and / or oxide-containing layers, and that

- The cover layer (4) consists of a cermet material of a metallic matrix and a ceramic component distributed therein, which constitutes 30 to 70 wt .-% of the cermet material.

4. Brake disc (1) according to claim 3,

characterized in that the metallic matrix is a high alloy CrNiMo steel which preferably has a composition comprising 28% by weight of chromium, 16% by weight of nickel, 4.5% by weight of molybdenum, 1.5% by weight of silicon, 1.75 Wt .-% carbon, balance iron, or is a NiCrMo alloy, which preferably has a composition comprising 20 to 23 wt .-% chromium, up to 5 wt .-% iron, 8 to 10 wt .-% molybdenum, 3.15 to 4.15% by weight of niobium and tantalum in total, remainder nickel, particularly preferably a composition comprising 21.5% by weight chromium, 2.5% by weight iron, 9.0% by weight Molybdenum, 3.7 wt .-% of niobium and tantalum in sum, balance nickel.

5. Brake disc (1) according to claim 3 or 4,

characterized in that

the ceramic component comprises oxide ceramics selected from Al ₂ O ₃ , Ti0 ₂ , Zr0 ₂ and MgAl ₂ 0 ₄ and combinations thereof, or the

Ceramic component Al ₂ 0 ₃ and at least one further oxide ceramic selected from the group comprising Ti0 ₂ , Zr0 ₂ , MgAI ₂ 0 ₄ , wherein Al ₂ 0 _{3 constitutes} a proportion of 60 to 90 wt .-% of the total ceramic component.

6. Brake disc (1) according to one of claims 3 to 5,

characterized in that

the surface layer (3) has, starting from the substrate (2), a diffusion layer (31), a nitride- and carbide-containing bonding layer (32) and an oxide layer (33), the diffusion layer (31) having a layer thickness of 0.1 to 0, 8 mm, the bonding layer (32) has a layer thickness of 2 to 30 μm, and the oxide layer (33) has a layer thickness of 1 to 5 μm.

7. Brake disc (1) according to one of claims 3 to 6,

characterized in that

between the cover layer (4) and the surface layer (3) an intermediate layer (10) is provided, which consists of a nickel-based alloy, preferably a nickel chromium alloy, or of the metallic matrix, wherein the

Intermediate layer (10) of the nickel-based alloy or the matrix metal has a layer thickness of 30 to 120 m.

8. A method for producing a brake disc (1) according to any one of claims 1 to 7, comprising the steps: - producing a brake disc blank (12),

Forming the cover layer (4),

Introducing the color changes (9) into the cover layer (6) by means of a pulsed laser in that the energy of the pulsed laser triggers chemical reactions or remelting processes.

9. The method according to claim 8,

comprising the steps before forming the cover layer (4):

- nitriding, carburizing, nitrocarburizing in a gas, plasma or

Salt bath method and / or by anodic or plasma oxidation, preferably nitrocarburizing, plasma activation and oxidation, of the substrate (2), at least on the friction surfaces (8), thereby forming the surface layer (3),

- Providing a cermet material of a metallic matrix and a ceramic component distributed therein, which makes up 30 to 70 wt .-% of the cermet material, and

- Applying the cermet material, in particular by thermal spraying, on the surface layer (3) and thereby forming the cover layer (4).