Brake Disc for a Motor Vehicle

Abstract

A brake disc for a motor vehicle is disclosed. The brake disc includes a substrate, in particular a grey cast iron substrate, at least one friction surface formed on the substrate and at least one cover layer applied at least to the at least one friction surface. The cover layer is harder and thinner than the substrate and color changes to enable identification are introduced in the cover layer by a pulsed laser.

Claims

1.-9. (canceled)

10. A brake disc for a motor vehicle, comprising: a substrate; a friction surface formed on the substrate; and a cover layer formed on the friction surface; wherein the cover layer is harder and thinner than the substrate; and wherein a color change is included in the cover layer, wherein the color change is formed by a pulsed laser, and wherein the brake disc is identifiable by the color change.

11. The brake disc according to claim 10, wherein the substrate is a grey cast iron.

12. The brake disc according to claim 10, wherein the cover layer has a microhardness of more than 300 HV.03 and/or the cover layer has ceramic and/or the cover layer has a thickness of less than 1000 m.

13. The brake disc according to claim 10, further comprising a surface layer formed between the substrate and the cover layer wherein the surface layer comprises nitride, carbide, and/or oxide containing layers; wherein the cover layer consists of a cermet material made of a metallic matrix and a ceramic component distributed in the cermet material and wherein the ceramic component makes up 30 to 70% b. w. of the cermet material.

14. The brake disc according to claim 13, wherein: the metallic matrix is a high alloy CrNiMo steel which has a composition comprising 28% b. w. chromium, 16% b. w. nickel, 4.5% b. w. molybdenum, 1.5% b. w. silicon, 1.75% b. w. carbon, and the rest iron, or is an NiCrMo alloy which has a composition comprising 20 to 23% b. w. chromium, up to 5% b. w. iron, 8 to 10% b. w. molybdenum, 3.15 to 4.15% niobium and tantalum in total, and the rest nickel.

15. The brake disc according to claim 13, wherein the metallic matrix is an NiCrMo alloy which has a composition comprising 21.5% b. w. chromium, 2.5% b. w. iron, 9.0% b. w. molybdenum, 3.7% b. w. niobium and tantalum in total, and the rest nickel.

16. The brake disc according to claim 13, wherein the ceramic component comprises oxide ceramics which are selected from the group consisting of Al2O3, TiO2, ZrO2 and MgAl2O4 and combinations thereof or wherein the ceramic component comprises Al2O3 and at least one further oxide ceramic selected from the group consisting of TiO2, ZrO2, MgAl2O4, wherein Al2O3 makes up a proportion of 60 to 90% b. w. of total ceramic components.

17. The brake disc according to claim 13, wherein the surface layer, starting from the substrate, has a diffusion layer, a nitride and carbide containing connection layer, and an oxide layer, wherein the diffusion layer has a thickness of 0.1 to 0.8 mm, the connection layer has a thickness of 2 to 30 m, and the oxide layer has a thickness of 1 to 5 m.

18. The brake disc according to claim 13, further comprising an intermediate layer disposed between the cover layer and the surface layer, wherein the intermediate layer consists of a nickel based alloy or of the metallic matrix and wherein the intermediate layer has a thickness of 30 to 120 m.

19. A method for producing a brake disc according to claim 10, comprising the steps of: producing a brake disc blank; forming the cover layer; and introducing of the color change into the cover layer by the pulsed laser, wherein energy of the pulsed laser triggers chemical reactions or fusing processes in the cover layer.

20. The method according to claim 19, further comprising the steps of: forming a surface layer on the substrate by nitriding, carburizing, or nitrocarburizing in a gas, plasma or salt bath method and/or by anodic or plasmaoxidation oxidizing of the substrate at least on the friction surface; providing a cermet material made of a metallic matrix and a ceramic component distributed within the cermet material, wherein the ceramic component makes up 30 to 70% b. w. of the cermet material; and applying the cermet material on the surface layer to form the cover layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is an overview of the brake disc according to the invention having several dents,

[0045] FIG. 2 is a sectional depiction of a section of the brake disc, in the area of a dent, along the line AA in FIG. 1,

[0046] FIG. 3 is a sectional depiction of a section of the brake disc, in the area of a dent having an alternative shape of the dent, along the line AA in FIG. 1,

[0047] FIG. 4 is a cross-sectional view through a section of a brake disc according to the invention without dents, having a hardened surface layer, a further nickel based intermediate layer and a cover layer,

[0048] FIG. 5 is a cross-sectional view through a section of a brake disc according to the invention having the surface layer formed of diffusion layer, connecting layer and oxide layer, a further nickel based intermediate layer and a cover layer, and

[0049] FIG. 6 is a microscopic image of the microsection through a section of the brake disc according to the invention having a profiled surface and a hardened surface layer, a further nickel based intermediate layer and a cover layer.

DETAILED DESCRIPTION OF THE DRAWINGS

[0050] The invention relates to a brake disc 1 having a substrate 2, in particular having a grey cast iron substrate, whose corrosion and wear properties are improved by a hardened surface layer 3 and a cover layer applied on top of it 4, where applicable more layers as well, wherein color changes 9 and, if applicable, dents 6, which do not pierce through the cover layer, are introduced in the cover layer. The layers prevent or reduce the broadening of tears, for example, that could appear on the surface during the service of the brake disc 1. Due to the fact that the spreading of tears into the substrate 2 is prevented, a corrosive infiltration of the layers is also effectively prevented, such that failure of the brake disc 1, for example through delamination, does not occur, or only occurs much later. The dents 6 can be designed to clean the brake pad or be formed as wear markings, for example.

[0051] A brake disc 1 presented in FIG. 1 has a hub 7 and at least one, for example two, friction surfaces 8, which are arranged coaxially to the hub. When braking, brake pads are applied to the friction surfaces. The friction surfaces 8 each have the surface layer 3 and the cover layer 4 applied on top of them. In every cover layer, several, for example four, dents are introduced.

[0052] In order to not destroy the corrosion protection effect of the cover layer 4, the dents 6 are only introduced in the cover layer 4, meaning they do not pierce through the cover layer 4. The remaining thickness of the cover layer 4 under the dents 6 should be large enough to avoid any further crack formation in the cover layer 4.

[0053] The dents 6 can be introduced into the cover layer 4 by means of a pulsed laser. With the pulsed laser the cover layer 4 can be treated without exerting large amounts of force on the cover layer 4. In this way, damages to the cover layer 4, even with small thicknesses of the cover layer 4, can be avoided.

[0054] Additionally, the pulsed laser enables the dents 6 to be formed virtually at random. For example, steep edges or smooth transitions between the surface and the dent 6 are possible.

[0055] Moreover, a color change 9 of the surface can also be made possible by means of the pulsed laser. In this way, serial numbers, type numbers or trademarks, for example, can be applied to the friction surfaces 8 of the brake disc 1. Likewise, it is possible to use a dent 6 to identify the brake disc 1.

[0056] In the following, the embodiment of an exemplary cover layer 4 will be explained, in which color changes 9 according to the invention can be introduced.

[0057] On the surface of the substrate 2 which forms the base plate of the brake disc 1, a hardened surface layer 3 is formed by nitriding, carburizing, nitrocarburizing and/or oxidizing, onto which a cover layer 4 is applied. The cover layer 4 consists of a cermet material made of a metallic matrix and a ceramic component distributed in it, the component making up 30 to 70% b. w. of the cermet material.

[0058] An alternatively designed brake disc, presented in FIG. 4, has an additional intermediate layer 10, made of a nickel based alloy, between the hardened surface layer 3 and the cover layer 4, preferably a corrosion resistant nickel chromium alloy, capable of withstanding high temperatures.

[0059] The production of a brake disc 1 according to the invention is explained below by reference to FIG. 5, in which the layers of a brake disc 1 according to the invention are outlined in more detail in an embodiment having an additional intermediate layer 10.

[0060] A brake disc according to the invention has the hardened surface layer 3 on the substrate 2, which is a cast brake disc blank, the surface layer 3 being preferably formed by nitriding, plasma-activating and oxidizing, according to the IONIT OX method, where applicable also by other nitriding, carburizing, nitrocarburizing and/or oxidization processes. Optionally, the surface of the substrate 2 can be mechanically profiled beforehand. The surface layer 3, starting from the substrate 2, is composed of a diffusion layer 31, a compound layer 32 and an oxide layer 33. During the nitrocarburizing, nitrogen and carbon penetrate the surface of the substrate 2, wherein in the connecting layer 32, whose thickness is in a range from 2 to 30 m, predominantly iron nitride or carbon nitride are formed, as well as iron nitride and other nitrides in smaller quantities. Under the connecting layer 32, the diffusion layer 31 extends into the substrate 2, the diffusion layer having a lower concentration of nitrogen and carbon diffused in than in the connecting layer 32, and the nitrogen is in solution in the substrate structure, alongside the other nitrides, carbides and nitride precipitation. The thickness of the diffusion layer 31 ranges from 0.1 to 0.8 mm, also depending on the conditions of treatment and the properties of the substrate.

[0061] The surface of the connecting layer 32 is oxidized after plasma activation, such that a largely sealed oxide layer 33 made of Fe.sub.3O.sub.4, with a thickness ranging from 1 to 5 m, is formed on the connection layer 32, which has a defined pore structure.

[0062] In order to obtain the layer construction 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 for forming the cover layer 4 is applied. The intermediate layer 10 can have a thickness ranging from 30 to 120 m and the cover layer 4 a thickness ranging from 100 to 500 m.

[0063] Between the intermediate layer 10 and the oxide layer 33in exemplary embodiments without the intermediate layer 10 correspondingly between the cermet cover layer 4 and the oxide layer 33there is a mixed zone 11, in which the iron oxide of the oxide layer 33 is combined with the nickel based alloy or the matrix metal of the intermediate layer 10 (or 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 mixed zone 11 between the cover layer 4 and the intermediate layer 10. The thickness of the mixed zone 11 can vary depending on the type of application and parameters of application.

[0064] Both the application of the nickel based alloy or the matrix metal for forming the intermediate layer 10, and the application of the cermet material for forming the cover layer 4, can be carried out by thermal spraying.

[0065] The photographic microscope image in FIG. 6 shows a substrate 2 profiled on the surface. The hardened surface layer 3 is on the surface of the substrate 2 having a thickness of approx. 30 m of compound layer 32 and 3 m of oxide layer 33, and is indicated by the dotted line. In this exemplary embodiment, a nickel based intermediate layer 10 with a thickness of on average ca. 100 m is applied to the profiled substrate 2 or the surface layer 3. As can be seen in the image, the thickness of the intermediate layer 10 varies because of the profiled surface of the substrate 2. The cover layer 4 made of cermet has an average thickness of approx. 350 m. Variations in the thickness also arise here from the profiled surface of the substrate 2, which, however, advantageously makes for a better connection between the cover layer 4 and the substrate 2 coated with the intermediate layer 10, by this interlocking effect.

[0066] The cover layer 4 as well as the layers 3, 10 lying below it can be restricted to tribologically loaded surfaces, meaning to the friction surfaces of the brake disc.

[0067] The matrix metal can be a highly alloyed CrNiMo steel or an NiCrMo alloy. Nickel-based, preferably NiCr alloys or pure matrix metal without ceramic components, are possibilities for the additional intermediate layer 10.

[0068] A CrNiMo steel suitable for forming the metallic matrix of the cover layer 4 has the composition Fe 28Cr 16 Ni 4.5 Mo 1.5 Si 1.75 C. Suitable NiCrMo alloys comprise compositions of Ni 20-23Cr<5Fe 8-10Mo 3.15-4.15Nb(+Ta) (Inconel 625, Special Metals Corporation, Huntington, W.V., USA), in particular Ni 21.5Cr 2.5Fe 9,0Mo 3.7 (Nb+Ta) is preferably suitable.

[0069] Other nickel based alloys, in particular NiCr alloys, are also possibilities as materials to form the intermediate layer 10.

[0070] The ceramic component of the cover layer 4 comprises oxide ceramics such as Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2 and MgAl.sub.2O.sub.4 (Spinell). These can be chosen individually or in combinations as reinforced ceramic components of the cermet. In this way, the ceramic component alongside Al2O3 as the main component can, for example, have at least one further oxide ceramic as an accessory component, which is chosen from the group comprising TiO.sub.2, ZrO.sub.2, MgAl.sub.2O.sub.4. The proportion of Al.sub.2O.sub.3 in the total ceramic component, whose proportion in cermet material is in the range of 30 to 70% b. w., can thereby make up 60 to 90% b. w. The other oxide ceramics TiO.sub.2, ZrO.sub.2 and/or MgAl.sub.2O.sub.4 are thus correspondingly present, with a proportion of 10 to 40% b. w. of the total ceramic component. The proportion of Al.sub.2O.sub.3 of the total ceramic components is preferably in the range of 75 to 85% b. w., preferably at 80% b.w.

[0071] The cover layer 4 applied by thermal spraying, for example, and made of the cermet material has a porosity of under 5% and a microhardness of between 300 HV.03 and 1000 HV.03.