Friction Brake Body for a Friction Brake of a Motor Vehicle, Method for Producing a Friction Brake

Abstract

The disclosure relates to a friction brake body for a friction brake of a motor vehicle, in particular a brake disc, wherein the friction brake body comprises a base body made from gray cast iron, and at least one wear resistant layer formed at least in areas on the base body. The wear resistant layer is a laser alloyed or laser dispersed edge layer of the base body and comprises at least one additive.

Claims

1. A friction brake element for a brake disc of a friction brake of a motor vehicle, comprising: a main element made of gray cast iron; and at least one antiwear layer present at least in regions on the main element, wherein the at least one antiwear layer is one of a laser-alloyed and laser-dispersed surface layer of the main element, and comprises at least one additive.

2. The friction brake element as claimed in claim 1, wherein the at least one additive comprises carbides selected from a group consisting of chromium carbide, niobium carbide, titanium carbide, tungsten carbide, molybdenum carbide, and vanadium carbide.

3. The friction brake element as claimed in claim 1, wherein the at least one additive comprises chromium or ferrochromium and at least one further carbide-forming element selected from a group consisting of titanium, niobium, vanadium, tungsten, and molybdenum.

4. The friction brake element as claimed in claim 1, wherein the at least one antiwear layer has a martensitic basic microstructure after the one of laser alloying and laser dispersion.

5. A friction brake for a motor vehicle, having at least one brake disc configured to be joined in a fixed manner to a wheel of the motor vehicle and having at least one movable brake pad assigned to the brake disc, wherein the brake disc includes a friction brake element as claimed in claim 1.

6. A process for producing a friction brake element for a friction brake of a motor vehicle, comprising: making a main element of the friction brake element from gray cast iron; and providing the main element, at least in regions, with at least one antiwear layer, wherein the at least one antiwear layer is produced by one of laser alloying and laser dispersion of at least one additive with or in a surface layer of the main element.

7. The process as claimed in claim 6, wherein the surface layer of the main element is melted to form a melt and the melt is subsequently provided with the at least one additive during the laser alloying or laser dispersion.

8. The process as claimed in claim 7, wherein the at least one additive is introduced in powder form into the melt.

9. The process as claimed in claim 6, wherein carbides selected from a group consisting of chromium carbide, niobium carbide, titanium carbide, tungsten carbide, molybdenum carbide, and vanadium carbide, are used as the at least one additive.

10. The process as claimed in claim 6, wherein chromium or ferrochromium and at least one further carbide-forming element selected from a group consisting of titanium, niobium, vanadium, tungsten, and molybdenum, are used as the at least one additive.

11. The process as claimed in claim 6, wherein a martensitic basic microstructure is produced in the at least one antiwear layer after the laser alloying or laser dispersion.

12. The process as claimed in claim 10, wherein: the surface layer of the main element is melted to form a melt and the melt is subse-quently provided with the at least one additive during the laser alloying or laser dispersion; and more chromium is added to the melt than an amount of free carbon available for formation of chromium carbide in the melt in order to ensure a corrosion resistance of the at least one antiwear layer.

13. The process as claimed in claim 6, further comprising: cooling the surface layer after the laser alloying or laser dispersion; and carrying out at least one of a laser hardening, an induction hardening, and a flame hardening after cooling.

14. The process as claimed in claim 6, further comprising; cooling the surface layer after the laser alloying or laser dispersion; and heat treating at least the surface layer at least once after cooling.

Description

[0022] FIG. 1 shows, in a simplified perspective view, a friction brake element 1 which is configured as brake disc 2 for a friction brake, which is not shown in more detail here, of a motor vehicle. The brake disc 2 has a main element 3 made of gray cast iron, which is configured as an annulus. A brake disc chamber which is optionally present on the brake disc 2 is not shown in FIG. 1.

[0023] On each of its two faces, the main element 3 has an annular frictional contact surface 4 which is provided with an antiwear layer 5. In the intended use, the antiwear layer 5 forms the contact partner of one or more brake pads of the friction brake which can be pressed against the brake disc to achieve friction braking. The friction between brake pad and brake disc 2 or friction brake element 1 arising during friction braking results in abrasion on the friction brake element 1 which leads to wear of the friction brake element 1 and also to brake dust which can get into the surroundings of the motor vehicle. This wear and the brake dust are reduced by the antiwear layer 5. In addition, high corrosion resistance of the antiwear layer is provided.

[0024] The antiwear layer 5 is for this purpose a laser-alloyed and/or laser-dispersed surface layer 6 of the main element 3, which comprises at least one additive 9.

[0025] FIG. 2 shows a production process for the brake disc in a simplified sectional view. The main element 3 and its surface layer 6 in which the antiwear layer 5 is produced by laser alloying are shown. To effect laser alloying, a laser beam 7 is passed over the main element 3, with the laser beam being sufficiently energy-rich for the surface layer 6 of the main element 3 to melt so as to give a melt 8. At least one pulverulent additive 9 is introduced in this melt 8. Compared to laser buildup welding in which the additive 9 can be at least partially liquefied before reaching the melt, both the amount and the rate of introduction of the additive 9 is significantly lower in the case of laser alloying, so that the additive 9 introduced is, in particular, at least largely melted in the melt 8 and together with the molten material of the main element 3 leads to a zone having altered chemical compositions in the region close to the surface or the surface layer 6 of the main element 3.

[0026] The hardness and corrosion resistance of the surface layer 6 is increased by the alloying-in of the abovementioned metallic or ceramic powders. Compared to conventional antiwear layers which are applied by means of laser buildup welding or thermal spraying processes, the present friction brake element 1 has a significant cost advantage brought about by a significantly decreased amount of additive. Due to the increased wear and corrosion resistance and the resulting reduced brake duct emission, advantages in respect of environmental protection are also obtained.

[0027] FIG. 3 shows the production process of the friction brake element 1 in a simplified flow diagram.

[0028] In a first step S1, a main element 3 made of gray cast iron is provided. Here, the main element 3 is manufactured in a conventional way so that it has an annular configuration and has an annular frictional contact surface 4 for a brake pad of the friction brake on each face.

[0029] In the subsequent step S2, the frictional contact surface is provided with the antiwear layer 5 by the surface layer 6 of the main element 3 being melted in a first step S4_1 and the at least one additive 9 being introduced in powder form into the resulting melt in a subsequent step S4_2. In step S4_1, the surface layer 6 is, in particular, partially melted by scanning with the laser radiation.

[0030] The melt is subsequently cooled in a step S5 and the antiwear layer 5 is obtained.

[0031] The additive(s) which is/are introduced into the, in particular superheated, melt 8 melt at least partially. As a result of convection, substantial homogenization of the melt bath composition occurs, as indicated by arrows in FIG. 2.

[0032] The friction brake element 1, in particular the antiwear layer 5, is optionally mechanically worked, in particular ground, in a concluding step S6 in order to obtain, for example, a desired surface roughness or geometry.

[0033] In a first working example, carbides, in particular from the group consisting of chromium carbide, niobium carbide, titanium carbide, tungsten carbide, molybdenum carbide and vanadium carbide, are added as additives 9 to the melt 8. These melt at least partially in the melt 8 and form a substance-to-substance bond to the gray cast iron matrix, thus forming the antiwear layer 5. If the additive 9 or supplementary material added does not melt or melts only insignificantly, the process is laser dispersion rather than laser alloying.

[0034] In a second working example, elemental chromium or more inexpensive ferrochromium and at least one further carbide-forming element, in particular from the group consisting of titanium, niobium, vanadium, tungsten and molybdenum, are added as additive 9 to the melt 8. During solidification, the added carbide-forming elements form metal carbides with the carbon present in the molten material of the main element 3 made of gray cast iron, as a result of which the content of free carbon in the laser-alloyed surface layer is reduced. Particular preference is given to adding more elemental chromium than the amount of free carbon present for formation of chromium carbide in the surface layer, so that the chromium remains substitutionally dissolved in the iron matrix of the laser-alloyed surface layer after solidification and in the presence of oxygen forms a passive layer on the surface, offering corrosion protection.

[0035] In step S5, cooling is preferably carried out so quickly that a martensitic basic microstructure is formed in the surface layer 6 immediately after laser alloying or laser dispersion. If the cooling rate is not sufficient, an additional hardening process, for example laser hardening, induction hardening or flame hardening, is preferably carried out after laser alloying and/or cooling.

[0036] The high hardness of the surface layer 6 is then based on the formation of martensite. The high heat resistance and thermal stability of the martensite up to temperatures of 600° C. is achieved by precipitation of fine metal carbides which reduce the carbon diffusivity in the iron lattice of the main element 3. To effect carbide precipitation, multiple heat treatment at temperatures of 550° C. is preferably carried out.