Hard material coated brake element and method for producing hard material coated brake element

Abstract

The invention relates to the field of vehicle technology and industrial equipment engineering, and relates to a hard material coated brake element. The aim of the invention is to provide a brake element which has a prolonged service life and at the same time a reduced production cost. This object is achieved by means of a brake element coated with a hard material, comprising a metallic main body having at least one region designed as a friction surface, on which at least one wear-resistant protective layer is arranged by means of a thermal coating method, wherein the wear-resistant protective layer is formed by at least one metal matrix material and a hard material particle aggregate which is at least partially embedded in the metal matrix material, and the hard material particle aggregate is connected with the metal matrix material in a material bonding manner. The hard material particle aggregate is formed by at least one hard material A, one hard material B and a hard material mixed crystal of the hard material A and the hard material B. In the hard material particle aggregate, the volume fraction of the hard material A is larger than that of the hard material B. For example, the brake element can be used for brake systems of motor vehicles and rail vehicles, or for brake systems of industrial equipment.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of automotive engineering and industrial plant engineering and to a hard material-coated brake element, which can be, for example, a brake disc or a brake drum. For example, a hard material-coated brake element according to the invention can be used in a brake system of a motor vehicle or a rail vehicle, in a disc brake system of a bicycle or in a brake system of an industrial plant or a wind turbine. BACKGROUND

[0002] A brake element has a plurality of functional areas. For example, a brake element in a motor vehicle is arranged on the front and rear axles and for this purpose has a contact surface which comes into contact with the wheel rim and the wheel hub.

[0003] Known brake discs are designed as solid constructions, as non-ventilated or internally ventilated brake discs, and can be made of metal or ceramic materials. Conventional brake drums are also solid constructions, sometimes with a cooling structure on the outside of the drum body, and are made of metal materials.

[0004] The friction surface of a brake element has a coating which is gradually worn away as a result of the braking process, by means of which the braking effect is achieved in cooperation with the brake pad.

[0005] Various brake elements with a wear coating are known from the prior art.

[0006] According to DE 197 11 830 A1, a brake pad of a sintered friction element, in particular a fiber-reinforced ceramic brake element, is known which comprises raw carbon and metal particles which are at least partially bonded to the raw carbon or pyrolytically formed carbon.

[0007] According to DE 100 56 161 A1, a brake disc and a method for producing it are known, in which a brake disc element made of cast iron material is provided with a metallic, non-ceramic coating at least in partial regions and at least on one of its axial outer surfaces. To prepare the contact surface of the main body element to be coated, the existing oxide layer and other impurities on the contact surface are removed and the contact surface is roughened by irradiation with microparticles in order to enhance the adhesion of the wear protection layer. Subsequently, the wear protection layer is applied to the contact surface of the main body element by means of a flame, arc or plasma injection molding coating method.

[0008] According to WO 2012 156 114 A1, furthermore, a brake disc and a method for producing a brake disc are disclosed, wherein the base element has at least one contact surface, which is provided with a wear-protective layer, wherein, in order to achieve a bond between the wear-protective layer and the base element, at least one contact surface of the base element is pretreated. The at least one pretreated contact surface of the base element has a surface topography which is modified by means of laser radiation having at least one predetermined parameter, in order to increase the positive-fit adhesion between the wear-protective layer and the base element.

[0009] According to DE 10 2019 207 291 A1, furthermore, a friction brake element, in particular a brake disc, for a motor vehicle is known, whose base element is made in particular from grey cast iron and has at least one wear-protective layer formed on a friction contact surface of the base element. It is provided that the wear-protective layer is made from a ferritic-austenitic steel and has embedded hard material particles, in particular finely dispersed hard material particles.

[0010] The disadvantage of the brake elements known from the prior art is that the wear-protective layer has a short service life and is expensive to produce. SUMMARY

[0011] The object of the present application is to provide a brake element which, while reducing the production costs, provides a longer service life.

[0012] This object is achieved by the application described in the patent claim. Advantageous embodiments are the content of the dependent claims, wherein the application also comprises combinations of the individual claims of the dependent claims, which are connected with the logic of "and", as long as these claims are not mutually exclusive.

[0013] The object is achieved according to the present application by a new brake element and a new method for producing the brake element, which has a longer service life and which can be produced quickly and economically efficiently.

[0014] The object is achieved by a hard material-coated brake element, which comprises a metal base element, which has at least one region designed as a friction surface, at least one wear-protective layer being arranged on the friction surface by means of a thermal coating method, wherein the wear-protective layer is formed at least from a metal base material and at least partially embedded hard material particle aggregates, which form a material bond with the metal base material, wherein the hard material particle aggregates are formed from at least one hard material A, at least one hard material B and at least a hard material mixed crystal of hard material A and hard material B, wherein in the hard material particle aggregates the volume fraction of hard material A is greater than the volume fraction of hard material B.

[0015] Advantageously, the hard material particle aggregates also contain at least one metallic additive material and / or alloying element.

[0016] Advantageously, aggregates of hard material particles can have a spherical particle morphology.

[0017] In an advantageous embodiment, hard material A and hard material B are selected from carbides, nitrides or carbonitrides.

[0018] In a particularly advantageous design of a braking element coated with a hard material, carbide A is TiC, and carbide B is selected from Mo2C, WC, Cr3C2, NbC and / or TaC.

[0019] Furthermore, it is advantageous to provide at least one bonding layer as a buffer layer between the metal substrate element and the wear-resistant protective layer.

[0020] It is also advantageous that the metal filler material, bonding layer and / or metal matrix material is an Fe-based material, particularly advantageously stainless steel; wherein, particularly advantageously, the stainless steel material is of grade EN 1.4016, EN 1.4404 or EN 1.4435.

[0021] In an advantageous embodiment of the invention, the content of carbide B is from 1 vol.% to 30 vol.% based on the total composition of the hard material particle aggregate.

[0022] Advantageously, in brake elements coated with hard materials, 10% to 60% of the surface of the wear-resistant protective layer is formed by aggregates of hard material particles.

[0023] Furthermore, it is advantageous that the hard material particle aggregates are uniformly or gradually distributed and embedded in the metal matrix material.

[0024] In an advantageous embodiment, the thermal conductivity of the hard material particle aggregate is < 120 W / mK.

[0025] Advantageously, the diameter of the hard material particle aggregates is from 10 µm to 100 µm, and particularly advantageously from 45 µm to 90 µm.

[0026] Advantageously, the layer height of the bonding layer is < 100 µm.

[0027] Furthermore, it is advantageous that the wear-resistant protective layer has a layer height of 25 µm to 175 µm.

[0028] Another advantage is that the wear-resistant protective layer and / or bonding layer have wear detection features.

[0029] According to the present invention, a method for manufacturing a braking element coated with a hard material is also provided, the method comprising the following steps: a) Provide a metal substrate element having at least one region designed as a friction surface. b) Provide a pre-formed aggregate of hard material particles having at least one hard material A, at least one hard material B, and a mixed crystal of hard materials A and B. c) Hard material particle aggregates and metal matrix material are simultaneously deposited on at least the area designed as a friction surface via at least two separate feeding devices using a thermal coating method, thereby creating a material bond and a wear-resistant protective layer. d) Process the surface of the wear-resistant protective layer.

[0030] In an advantageous embodiment of this method, it may be specified that a hard material particle aggregate is provided, which is composed of at least one hard material A, at least one hard material B, and a mixed crystal of hard materials consisting of at least hard material A and hard material B, wherein in the hard material particle aggregate, the volume fraction of hard material A is greater than the volume fraction of hard material B.

[0031] Advantageously, a bonding layer is provided as a buffer layer between the area of ​​the substrate element designed as a friction surface and the wear-resistant protective layer.

[0032] Another advantage is that the bonding layer and / or wear-resistant protective layer can be arranged in a locally generated protective gas atmosphere.

[0033] In an advantageous design of this method, the metal substrate element is preheated before thermal coating.

[0034] Laser metal deposition is a particularly advantageous thermal coating method.

[0035] Another advantage is that the surface of the wear-resistant protective layer can be processed by surface grinding.

[0036] According to the present invention, a braking element is provided, comprising a metal substrate element. The metal substrate element has at least one region designed as a friction surface, and at least one wear-resistant protective layer having an aggregate of hard material particles is formed on the friction surface by a thermal coating method.

[0037] Within the scope of this invention, hard materials should be understood as particles formed in such a way that at least one hard material A, at least one hard material B, and a mixed crystal formed from hard materials A and B are present, and metallic additives or alloying elements may also be present. The mixed crystal of hard materials is formed in the boundary region between hard materials A and B.

[0038] To improve the mechanical properties of hard material particle aggregates and thus the mechanical properties of wear-resistant protective layers, it is crucial in this invention that the volume fraction of hard material A in the hard material particle aggregates is greater than the volume fraction of hard material B.

[0039] Advantageously, at least one bonding layer can be provided as a buffer layer between the metal substrate element and the wear-resistant protective layer, for example, to facilitate enhanced adhesion and thus reduce the risk of delamination.

[0040] At least one wear-resistant protective layer and a possible bonding layer are applied by a thermal coating method, wherein laser metal deposition is advantageously used. The thermal coating method and the advantageous laser metal deposition offer significant technical advantages: highly precise, uniform, or gradient-distributed layers can be applied to the substrate element, and these coatings are permanently bonded to each other through material bonding, thereby effectively preventing delamination between the coating and the substrate element.

[0041] The heat input of the thermal coating method enables the formation of a material bond between the layer and the substrate, especially in laser metal deposition, which has significant advantages over thermal spraying processes: effectively preventing deformation of the hard material particle aggregates according to the invention. Furthermore, another advantage of laser metal deposition is that, by adjusting the intensity distribution of the laser spot, the adverse chemical and mechanical properties of hard material particle aggregates (e.g., reduced corrosion resistance of carburized, hardened, and wear-resistant protective layers) are almost completely avoided, especially for Fe-based base metals. This significantly improves material utilization, thereby substantially reducing manufacturing costs.

[0042] The wear-resistant protective layer comprises at least a metallic matrix material and at least partially embedded pre-formed hard material particle aggregates. The pre-formed hard material particle aggregates are manufactured in existing process steps via spray granulation and sintering, a process that advantageously produces spherical particle morphology. This spherical particle morphology of the hard material particle aggregates offers significant advantages: previously unfavorable, familiar irregular and sharp-edge particle morphologies on the surface, coarse, irregular, intact hard material particles, and defective wear-resistant protective layers are almost completely eliminated.

[0043] The advantageous spherical particle morphology of hard material aggregates not only extends the service life of braking components but also improves the tool life during surface finishing processes that may occur during manufacturing. Furthermore, forming a spherical particle morphology during the final finishing of the wear-resistant protective layer improves dimensional stability and reduces the fracture tendency of the hard material aggregates, thereby preventing damage and / or fracture of the hard material aggregates in the wear-resistant protective layer and ensuring an increased proportion of intact hard material aggregates in the tribological system.

[0044] Another significant technological advantage of employing spray granulation and sintering processes in the upstream manufacturing of hard material particle aggregates is that the hard material particles are formed in aggregate form, consisting of at least one hard material A, at least one hard material B, and mixed crystals of hard materials A and B. Advantageously, the hard material particle aggregates can contain metallic additives and / or alloying elements. The metallic additives and / or alloying elements can also exist in aggregate form within the hard material particles.

[0045] When a hard material particle aggregate is formed from at least one carbide A, at least one carbide B, and a mixed crystalline carbide composed of at least carbide A and B, and when the volume fraction of carbide A in the hard material particle aggregate is greater than the volume fraction of carbide B, the wear-resistant protective layer can achieve specific technical advantages and effects.

[0046] Surprisingly, the use of hard material particle aggregates and mixed crystalline carbides (advantageously TiC as carbide A, and Mo2C, WC, Cr3C2, NbC, and / or TaC as carbide B) resulted in an extremely fine grain structure with a uniform microstructure. These hard material particle aggregates exhibit higher hardness and fracture toughness than carbide A at increased density, thus significantly extending the service life of the wear-resistant protective layer and enhancing the heat resistance of braking components. Furthermore, the high density of the hard material particle aggregates reduces sedimentation and segregation, thereby improving storage capacity, metering, and conveying capabilities during the thermal coating process.

[0047] Another possibility is to consider Cr3C2 as carbide A. In this case, it is ruled out that Cr3C2 will simultaneously form carbide B, and it will not exist as a mixed crystalline carbide of carbide A and carbide B.

[0048] By selecting at least the metal matrix material and / or the additive material as an iron-based material, a particularly excellent integral connection is achieved between the advantageously configured bonding layer and the metal matrix component and the wear-resistant protective layer, wherein the metal matrix material is preferably stainless steel of material grade EN 1.4016, EN 1.4404 or EN 1.4435.

[0049] When the content of carbide B is between 1 vol.% and 30 vol.% based on the total composition of the hard material particle aggregate, the excellent properties of the hard material particle aggregate, such as high melting point and decomposition temperature, high hardness and improved thermal expansion behavior, can be advantageously achieved.

[0050] The wear-resistant protective layer has 10% to 60% of its surface formed by aggregates of hard material particles and / or the diameter of the hard material particle aggregates is 10 µm to 100 µm, advantageously 45 µm to 90 µm, which can achieve extended service life of braking components and reduced corrosion tendency.

[0051] Advantageously, the hard material particle aggregates can be uniformly or gradually distributed and embedded in the metal matrix material. According to the invention, the gradual distribution of the hard material particles should be understood as achieving a gradient within the layer thickness of the metal matrix material and / or in the circumferential region of the friction surface of the braking element. This gradient offers significant technical advantages in that it allows for adaptation and adjustment of the thermal balance within the braking element to different thermal loads, and thus the braking element can be individually configured for different applications. Advantageously, the thermal conductivity of the hard material particle aggregates embedded in the metal matrix material is < 120 W / mK.

[0052] To achieve a permanent, material-bonded connection between the bonding layer and the cast material of the metal substrate element, as well as the wear-resistant protective layer, the bonding layer height is advantageously < 100 µm. To reduce overall weight and stress in the braking element, the wear-resistant protective layer has an advantageously smaller height of 25 µm to 175 µm.

[0053] To improve traffic and maintenance safety, wear-resistant protective layers and / or bonding layers can be advantageously configured with wear detection features, which can identify the wear limit of braking components or wear-resistant protective layers.

[0054] According to the present invention, a method for manufacturing a braking element coated with a hard material is also provided, characterized by the following method steps: a) Provide a metal substrate element having at least one region designed as a friction surface. b) Provide a pre-formed aggregate of hard material particles having at least one hard material A, at least one hard material B, and a mixed crystal of hard materials A and B. c) Hard material particle aggregates and metal matrix material are simultaneously deposited on at least the area designed as a friction surface via at least two separate feeding devices using a thermal coating method, thereby creating a material bond and a wear-resistant protective layer. d) Process the surface of the wear-resistant protective layer.

[0055] Advantageously, a bonding layer can be arranged on the metal substrate element as a buffer layer. It is also advantageous to specify that the bonding layer and / or wear-resistant protective layer are arranged in a locally generated protective gas atmosphere, which is supplied in situ to the process during coating (advantageously by laser metal deposition welding) via a gas supply line connected to at least one supply device. This locally generated protective gas flow is coaxially aligned with the coating flow, preventing oxygen from being introduced into the coating process due to turbulence generated during laser metal deposition. Furthermore, since the locally generated protective gas is introduced in situ during the process, additional airflow can be directly formed at the feed device, thereby increasing the coverage area of ​​the coating region and reducing the oxygen protective gas coverage, thus providing a more efficient and economical method. Therefore, the use of a protective gas can reduce the oxygen content, thereby improving the oxidation resistance of the wear-resistant protective layer.

[0056] It was also found that the low oxygen content in the coated area led to improved wettability of the melt with the metal substrate elements and / or the substrate material of the bonding layer, especially during laser metal deposition under a locally generated protective gas atmosphere. This offers the technical advantage of significantly reducing the oxidation of hard material particle aggregates and the associated fume formation. The resulting wear-resistant protective layer exhibits significantly improved performance, characterized by low porosity and low defect rate.

[0057] In advantageous process steps, it can also be specified to preheat the metal substrate element before coating. The technical advantage of preheating the metal substrate element before thermal coating is that it reduces coating cycle time, which enables higher product yield, thereby reducing time and costs. Furthermore, it reduces temperature-induced stress, which significantly improves the dimensional stability of the braking element.

[0058] The present invention will be described in detail below based on exemplary embodiments. Detailed Implementation

[0059] To manufacture brake elements coated with a hard material, a brake disc blank with a friction surface formed from cast material is provided, which is produced as a metal matrix element in a thermal coating system. Hard material particle aggregates with a spherical granular morphology are provided and fed in powder form to a first feed device in an upstream manufacturing process via spray granulation and sintering. The hard material particles consist of: TiC as carbide A, WC as an aggregate of carbide B, and stainless steel material 316 L corresponding to material grade EN 1.4404. Carbide B is present at 10 vol% of the total composition of the hard material particles, and the hard material particle aggregates have 10 vol% stainless steel material 316 L. The hard material particle aggregates exist as individual carbides A and B, and as mixed crystalline carbides of carbides A and B, having a composition of TiC-WC and particle diameters between 45 µm and 90 µm. In addition, stainless steel of grade EN 1.4404 is supplied to the second feeding device as the metal substrate material for manufacturing the bonding layer and the wear-resistant protective layer. In the first method step, the brake disc is preheated to approximately 165°C, and then a bonding layer with a thickness of 85 µm is deposited on the friction surface region of the brake disc via laser metal deposition through the second feeding device under a locally generated protective gas atmosphere. During the coating of the bonding layer, the bonding layer material is bonded in situ to the casting material of the brake disc blank. Subsequently, a wear-resistant protective layer with a thickness of 180 µm containing hard material particle aggregates is supplied to the bonding layer via laser metal deposition under a locally generated protective gas atmosphere, wherein the supply of the metal substrate material via the second feeding device and the supply of the hard material particle aggregates via the first feeding device are performed separately. The proportion of hard material particle aggregates in the wear-resistant protective layer relative to the metal substrate material is < 40 vol.%. After the wear-resistant protective layer is applied, the surface is fully machined by surface grinding, with the final machining removing only 50-65 µm, thus completely eliminating runout error and layer thickness variation. After final machining, the brake disc will have a double-layer wear-resistant protective layer with a total layer thickness of <300 µm, of which the wear-resistant protective layer has a thickness of at least 100 micrometers.

Claims

1. A braking element coated with a hard material, comprising a metal substrate element having at least one region designed as a friction surface, wherein at least one wear-resistant protective layer is formed on the friction surface by a thermal coating method, wherein the wear-resistant protective layer is formed at least of a metal substrate material and at least partially embedded therein an aggregate of hard material particles, the aggregate of hard material particles being bonded to the metal substrate material, wherein the aggregate of hard material particles is formed of at least one hard material A, at least one hard material B, and at least a mixed crystal of hard materials A and hard material B, wherein in the aggregate of hard material particles, the volume fraction of hard material A is greater than the volume fraction of hard material B.

2. The braking element coated with a hard material according to claim 1, wherein the hard material particle aggregate further comprises at least one metallic additive material and / or alloying element.

3. The braking element coated with a hard material according to claim 1, wherein the hard material particle aggregate has a spherical particle morphology.

4. The braking element coated with a hard material according to claim 1, wherein the hard material A and the hard material B are selected from carbides, nitrides or carbonitrides.

5. The braking element coated with a hard material according to claim 1, wherein the hard material particle aggregate is formed of at least one carbide A, at least one carbide B, and a mixed crystalline carbide composed of at least said carbide A and said carbide B, and wherein in the hard material particle aggregate, the volume fraction of said carbide A is greater than the volume fraction of said carbide B.

6. The braking element coated with a hard material according to claim 5, wherein the carbide A is TiC.

7. The braking element coated with a hard material according to claim 5, wherein the carbide B is Mo2C, WC, Cr3C2, NbC and / or TaC.

8. The braking element coated with a hard material according to claim 1, wherein at least one bonding layer is provided as a buffer layer between the metal substrate element and the wear-resistant protective layer.

9. The braking element coated with a hard material according to claim 1 or 2, wherein the metal additive material, the bonding layer and / or the metal substrate material is an Fe-based material, particularly advantageously stainless steel.

10. The braking element coated with a hard material according to claim 9, wherein the stainless steel material is of grade EN 1.4016, EN 1.4404 or EN 1.4435.

11. The braking element coated with a hard material according to claim 1, wherein the content of the hard material B is from 1 vol.% to 30 vol.% based on the total composition of the hard material particle aggregate.

12. The braking element coated with a hard material according to claim 1, wherein 10% to 60% of the surface of the wear-resistant protective layer is formed by aggregates of hard material particles.

13. The braking element coated with a hard material according to claim 1, wherein the hard material particle aggregates are uniformly distributed or gradually distributed and embedded in the metal matrix material.

14. The braking element coated with a hard material according to claim 1, wherein the thermal conductivity of the hard material particle aggregate is < 120 W / mK.

15. The braking element coated with a hard material according to claim 1, wherein the diameter of the hard material particle aggregate is from 10 µm to 100 µm, advantageously from 45 µm to 90 µm.

16. The braking element coated with a hard material according to claim 1, wherein the layer height of the bonding layer is < 100 µm.

17. The braking element coated with a hard material according to claim 1, wherein the wear-resistant protective layer has a layer height of 25 µm to 175 µm.

18. The braking element coated with a hard material according to claim 1, wherein the wear-resistant protective layer and / or the bonding layer have wear detection features.

19. A method for manufacturing a braking element coated with a hard material, the method comprising the following steps: a) Provide a metal substrate element having at least one region designed as a friction surface. b) Provide a pre-formed aggregate of hard material particles, comprising at least one hard material A, at least one hard material B, and a mixed crystal of hard material A and hard material B. c) The hard material particle aggregate and the metal matrix material are simultaneously deposited on at least the area designed as a friction surface via at least two separate feeding devices using a thermal coating method, thereby creating a material bond and a wear-resistant protective layer. d) Process the surface of the wear-resistant protective layer.

20. The method of claim 19, wherein a pre-formed hard material particle aggregate is provided, having at least one hard material A, at least one hard material B, and a mixed crystal of said hard material A and said hard material B, wherein in the hard material particle aggregate, the volume fraction of said carbide A is greater than the volume fraction of said carbide B.

21. The method of claim 19, wherein the bonding layer is provided as a buffer layer between the region of the substrate element designed as a friction surface and the wear-resistant protective layer.

22. The method of claim 19, wherein the bonding layer and / or the wear-resistant protective layer are arranged in a locally generated protective gas atmosphere.

23. The method of claim 19, wherein the metal substrate element is preheated prior to thermal coating.

24. The method of claim 19, wherein the thermal coating is performed by laser metal deposition.

25. The method of claim 19, wherein the surface of the wear-resistant protective layer is processed by surface grinding.