Brake disc for motor vehicles and manufacturing process for such a brake disc

Abstract

Motor vehicle brake disc comprising at least one external surface (2a, 3a) having a coating (6), the coating (6) comprising: a first layer (7) disposed at least partially on the external surface (2a, 3a), the first layer (7) comprising a steel having a chromium content of between 10 and 20% by mass relative to the total mass of the steel;a second layer (8) disposed on the first layer (7), the second layer (8) comprising a steel matrix having a chromium content of between 10 and 20% by mass relative to the total mass of the steel, and a content of between 15 and 40% by volume of at least one carbide relative to the total volume of the second layer, the carbide being selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof, preferably selected from niobium carbide, titanium carbide or a mixture thereof; the coating (6) being obtained by a very high-speed laser deposition technique known as EHLA. Figure for the abstract: Fig 1;

Description

Title of the invention: Brake disc for motor vehicles and method for manufacturing such a brake disc

[0001] The present invention relates, in general, to the control of pollutant emissions from a motor vehicle and, more specifically, to the emission of fine particles during braking by a motor vehicle.

[0002] In particular, the invention relates to a brake disc for a motor vehicle and a method for manufacturing such a brake disc.

[0003] In a motor vehicle, the wear of the brake disc as well as the friction between the brake pads and the brake disc during braking results in the release of polluting particles into the atmosphere.

[0004] Emissions of particles less than 10 pm (PM10), known as fine particles, are particularly dangerous for the respiratory tracts of populations.

[0005] Therefore, within the framework of a future Euro 7 standard, a new European regulation aims to limit fine particle emissions during braking of private and commercial motor vehicles.

[0006] There is a device for capturing the released particles, based on the operation of suction turbines triggered during braking.

[0007] However, this device is bulky and only captures particles during braking.

[0008] Another solution is to integrate particulate filters into the braking system.

[0009] However, these filters are particularly expensive.

[0010] There are also brake discs made of added cast iron, containing additive elements, such as vanadium.

[0011] Although doping cast iron improves the wear and thermal fatigue resistance properties of the brake disc and thus reduces the release of particles, this solution is not sufficient for the most powerful motor vehicles.

[0012] The invention therefore aims to remedy these drawbacks and to propose a solution aimed at optimizing the limitation of brake disc wear, in particular for motor vehicles, and the reduction of the release of fine particles.

[0013] A brake disc for a motor vehicle is therefore proposed, comprising at least one external surface with a coating, the coating comprising:

[0014] a first layer disposed on all or part of the external surface, the first layer comprising a steel having a chromium content of between 10 and 20 % by mass relative to the total mass of the steel;

[0015] a second layer disposed on the first layer, the second layer comprising a steel matrix having a chromium content of between 10 and 20% by mass relative to the total mass of the steel, and a content of between 15 and 40% by volume of at least one carbide relative to the total volume of the second layer, the carbide being selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof, preferably selected from niobium carbide, titanium carbide or a mixture thereof;

[0016] the coating being obtained according to a very high speed laser material deposition technique known as EHLA.

[0017] Preferably, the coating is a two-layer coating comprising only said first layer and said second layer.

[0018] According to one characteristic, the steel of the first layer and / or the steel of the second layer can be a ferritic steel.

[0019] Preferably, ferritic steel is a steel consisting of a chromium content of between 16 and 18% by mass, a silicon content of less than or equal to 1% by mass, a nickel content of less than or equal to 0.6% by mass, a manganese content of less than or equal to 1% by mass, a carbon content of less than or equal to 0.08% by mass, a molybdenum content of less than or equal to 1% by mass, a phosphorus content of less than or equal to 0.045% by mass, a sulfur content of less than or equal to 0.03% by mass, a titanium content of less than or equal to 0.01% by mass, optionally other addition elements such as copper, vanadium, niobium, or tin, the remainder being iron and unavoidable impurities.

[0020] In one embodiment, the second layer may comprise a titanium carbide content of between 15 and 25% by volume, preferably between 17 and 23% by volume, preferably still between 19 and 21% by volume, relative to the total volume of the second layer.

[0021] In another embodiment, the second layer may comprise a niobium carbide content of between 25 and 35% by volume, preferably between 27 and 33% by volume, preferably still between 29 and 31% by volume, relative to the total volume of the second layer.

[0022] In another embodiment, the second layer may comprise a mixture of carbides, the content of each carbide in the mixture of carbides being between 5 and 20% by volume, preferably between 5 and 10% by volume, relative to the total volume of the second layer.

[0023] According to one feature, the second layer may comprise a mixture of carbide of niobium and titanium carbide, the niobium carbide content being between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer, and a titanium carbide content of between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer.

[0024] Advantageously, the material of the brake disc on which the coating is disposed can be cast iron, preferably lamellar graphite cast iron.

[0025] Preferably, the brake disc may include first and second opposing faces having respectively first and second external surfaces, each of the first and second external surfaces including a friction track intended to cooperate with a brake pad, the coating being disposed at least partially on the friction tracks, preferably only disposed on the friction tracks.

[0026] The invention also relates to a method for manufacturing a brake disc as previously described, comprising the formation of the first and second layers of the coating by a very high speed laser material deposition technique known as EHLA.

[0027] Preferably, the step of forming the second layer of the coating in the manufacturing process includes the use of cermets.

[0028] The invention also relates to a motor vehicle comprising at least one brake disc as previously described.

[0029] Other purposes, advantages and features will become apparent from the following description, given for illustrative purposes only and with reference to the accompanying drawings on which:

[0030] [Fig-1] is a schematic cross-sectional view of a brake disc for a motor vehicle according to an embodiment of the invention.

[0031] [Fig.2] is a detailed view of a friction track of a brake disc illustrated in the [Fig.l].

[0032] [Fig.3] represents the operating mode of the EHLA technique.

[0033] In what follows, and unless otherwise indicated, the bounds of a domain of values ​​are included in that domain, in particular in the expression "between".

[0034] Furthermore, the expression "at least one" used in this description is equivalent to the expression "one or more".

[0035] Fig. 1 illustrates a brake disc 1 for a motor vehicle, comprising at least one external surface.

[0036] In the illustrated example, the brake disc 1 is an annular structure comprising a first face 2 and a second face 3 opposite to the first face 2.

[0037] The first face 2 has a first external surface 2a and the second face 3 has a second external surface 3a.

[0038] The first and second external surfaces 2a and 3a each comprise a friction track, respectively a first friction track 4 and a second friction track 5, intended to cooperate with a brake pad (not shown).

[0039] Each friction track 4, 5 forms a contact area with a brake pad so that the friction of the fixed brake pads on the first and second friction tracks 4, 5 of the movable brake disc 1 leads to the braking of the motor vehicle.

[0040] The first and second external surfaces 2a and 3a of the brake disc 1 are coated, at least partially, with a coating 6.

[0041] Advantageously, the coating 6 is formed on the friction tracks 4 and 5.

[0042] The coating 6 is preferably formed only on the friction tracks 4 and 5 in order to limit the cost of brake disc 1.

[0043] The coating 6 can be formed on all or part of the friction tracks 4 and 5, preferably on all of the friction tracks 4 and 5.

[0044] The material of the brake disc 1 on which the coating 6 is formed is preferably cast iron. Cast iron is a particularly economical material and its high thermal conductivity properties allow it to store heat and dissipate the heat produced by friction during braking.

[0045] Advantageously, the material of the brake disc 1 on which the coating 6 is formed can be lamellar graphite cast iron, such as GJL 150 cast iron.

[0046] GJL 150 cast iron consists of a carbon content of 3.7% by mass, a silicon content of 1.87% by mass, a manganese content of 0.61% by mass, a sulfur content of less than 0.1% by mass, a phosphorus content of less than 0.1% by mass, a copper content of less than 0.1% by mass, a nickel content of 0.1% by mass, a chromium content of less than 0.1% by mass, a molybdenum content of less than 0.1% by mass, a titanium content of less than or equal to 0.1% by mass, a vanadium content of less than 0.1% by mass, a niobium content of less than 0.1% by mass, a selenium content of less than 0.1% by mass, the remainder being iron and unavoidable impurities.

[0047] The coating 6 comprises a first layer 7 disposed in contact with the first and second external surfaces 2a and 3a.

[0048] The first layer 7 comprises a steel having a chromium content of between 10 and 20% by mass relative to the total mass of the steel of the first layer 7.

[0049] Preferably, the steel of the first layer 7 is a ferritic steel.

[0050] Ferritic steel is defined as steel whose crystal structure is body-centered cubic and containing a chromium content of between 10 and 20% by mass relative to the total mass of the steel.

[0051] Ferritic steels are particularly advantageous given their low tendency to form cracks, notably due to their low coefficient of thermal expansion, close to that of the cast iron used.

[0052] Preferably, the ferritic steel of the first layer can be a ferritic stainless steel consisting of a chromium content of between 16 and 18% by mass, a silicon content of less than or equal to 1% by mass, a nickel content of less than or equal to 0.6% by mass, a manganese content of less than or equal to 1% by mass, a carbon content of less than or equal to 0.08% by mass, a molybdenum content of less than or equal to 1% by mass, a phosphorus content of less than or equal to 0.045% by mass, a sulfur content of less than or equal to 0.03% by mass, a titanium content of less than or equal to 0.01% by mass, optionally other addition elements such as copper, vanadium, niobium, or tin, the remainder being iron and unavoidable impurities.

[0053] Preferably, the total unavoidable impurities represent less than 0.15% by mass.

[0054] Preferably, each unavoidable impurity is present at less than 0.05% by mass.

[0055] According to one example, the ferritic steel of the first layer 7 can be a ferritic stainless steel generally known as 430L steel or by its European designation X2Crl7, consisting of a chromium content of 16.29% by mass, a silicon content of 0.94% by mass, a nickel content of 0.53% by mass, a manganese content of 0.28% by mass, a carbon content of 0.08% by mass, a molybdenum content of 0.06% by mass, a phosphorus content of 0.031% by mass, a sulfur content of 0.02% by mass, a titanium content of 0.003% by mass, the remainder being iron and unavoidable impurities, the percentages being defined in relation to the total mass of the steel.

[0056] The coefficient of thermal expansion of ferritic steels is close or similar to that of cast iron.

[0057] In particular, the coefficient of thermal expansion of 430L steel, which is equal to 10.4.10-6 Kl, is very close to that of GJL 150 lamellar graphite cast iron which is equal to 10.7.10-6 KL. This has a favorable effect for limiting the number and depth of cracks.

[0058] The coating 6 further comprises a second layer 8 disposed on the first layer 7.

[0059] The first layer 7 forms an adhesion layer between the first and second external surfaces 2a and 3a of the brake disc 1 and the second layer 8.

[0060] The second layer 8 comprises a steel matrix having a content of chromium content between 10 and 20% by mass relative to the total mass of the steel.

[0061] Preferably, the steel of the matrix of the second layer 8 and the steel of the first layer 7 are identical so as to increase the affinity and therefore the adhesion between the first and second layers 7 and 8.

[0062] In this way, the steel of the second layer 8 is preferably a ferritic steel.

[0063] Preferably, the ferritic steel of the second layer 8 can be a ferritic stainless steel consisting of a chromium content of between 16 and 18% by mass, a silicon content of less than or equal to 1% by mass, a nickel content of less than or equal to 0.6% by mass, a manganese content of less than or equal to 1% by mass, a carbon content of less than or equal to 0.08% by mass, a molybdenum content of less than or equal to 1% by mass, a phosphorus content of less than or equal to 0.045% by mass, a sulfur content of less than or equal to 0.03% by mass, a titanium content of less than or equal to 0.01% by mass, optionally other addition elements other than the aforementioned elements such as copper, vanadium, niobium, or tin, the remainder being iron and unavoidable impurities.

[0064] Preferably, the total unavoidable impurities represent less than 0.15% by mass.

[0065] Preferably, each unavoidable impurity is present at less than 0.05% by mass.

[0066] According to one example, the ferritic steel of the second layer 8 can be a ferritic stainless steel generally known as 430L steel, consisting of a chromium content of 16.29% by mass, a silicon content of 0.94% by mass, a nickel content of 0.53% by mass, a manganese content of 0.28% by mass, a carbon content of 0.08% by mass, a molybdenum content of 0.06% by mass, a phosphorus content of 0.031% by mass, a sulfur content of 0.02% by mass, a titanium content of 0.003% by mass, the remainder being iron and unavoidable impurities, the percentages being defined in relation to the total mass of the steel.

[0067] In addition, the second layer 8 comprises a content of between 15 and 40% by volume of at least one carbide relative to the total volume of the second layer.

[0068] The carbide(s) are chosen from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof.

[0069] Silicon carbide, chromium carbide, tungsten carbide, niobium carbide and titanium carbide have the advantage of being readily available in powder form, facilitating their deposition on the brake disc 1 by thermal spraying.

[0070] Silicon carbide, chromium carbide and titanium carbide are also particularly advantageous given their moderate cost and their re- properties high mechanical resistance.

[0071] Preferably, the carbide(s) are chosen from niobium carbide and titanium carbide, showing very good mechanical resistance performance, or a mixture of these.

[0072] Even more preferably, the carbide chosen is titanium carbide, which has similar mechanical and thermal properties to niobium carbide but is less expensive.

[0073] In one embodiment, the second layer 8 may comprise a titanium carbide content of between 15 and 25% by volume, preferably between 17 and 23% by volume, preferably still between 19 and 21% by volume, relative to the total volume of the second layer 8.

[0074] According to one example, the second layer 8 may comprise a titanium carbide content equal to 20% by volume relative to the total volume of the second layer 8.

[0075] In another embodiment, the second layer 8 may comprise a niobium carbide content of between 25 and 35% by volume, preferably between 27 and 33% by volume, preferably still between 29 and 31% by volume, relative to the total volume of the second layer.

[0076] According to one example, the second layer 8 may comprise a niobium carbide content equal to 30%.

[0077] In another embodiment, the second layer may comprise a mixture of carbides, the content of each carbide in the mixture of carbides being between 5 and 20% by volume, preferably between 5 and 10% by volume, relative to the total volume of the second layer.

[0078] By mixing several types of carbides in smaller proportions, it is possible to obtain a more economical coating 6.

[0079] According to one embodiment, the second layer 8 may for example comprise a mixture of niobium carbide and titanium carbide, the niobium carbide content being between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer, and a titanium carbide content being between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer.

[0080] According to one example, the second layer 8 may comprise a mixture of niobium carbide and titanium carbide, the niobium carbide content being 5% by volume and the titanium carbide content being 10% by volume, relative to the total volume of the second layer 8.

[0081] The first layer 7 forms an adhesion layer between the first and second external surfaces 2a and 3a and the second layer 8.

[0082] The coefficients of thermal expansion close to the substrate formed by the first and The second external surfaces 2a and 3a and the first layer 7 contribute to increasing this adhesion.

[0083] The second layer 8 forms a first resistant barrier allowing to reduce the occurrence of cracking due to friction between the coated brake disc 1 and the brake pads.

[0084] In addition to the second layer 8, the first layer 7 forms a second mechanical resistance barrier allowing the occurrence of cracking to decrease.

[0085] Preferably, the coating 6 is a two-layer coating comprising only said first layer and said second layer.

[0086] The bilayer structure of the coating 6 limits the number of interfaces where porosity can occur and cause decohesion of the coating 6, making it fragile under mechanical stress. The bilayer structure therefore results in a coating 6 that is more mechanically resistant than a structure with more than two interfaces.

[0087] The thickness of the coating 6 is between 300 and 500 pm, preferably between 350 and 450 pm.

[0088] Preferably, the thickness of the first layer 7 is between 100 and 200 pm.

[0089] Preferably, the thickness of the second layer 8 is between 100 and 200 pm.

[0090] The coating 6 is obtained using a very high speed laser material deposition technique called EHLA.

[0091] In the present invention, the deposition of materials by very high-speed laser means a thermal projection technique also known by the English name "Extreme high-speed laser application process" and by the acronym EHLA.

[0092] With reference to [Fig. 3], the EHLA technique, like the Laser Cladding technique from which it derives, relies on the use of a high-power industrial laser 9 to melt and / or weld metal powders. The powders, carried by a gas such as argon, form a powder stream 10 projected onto a substrate, thus creating a superposition of metallurgical bonds. This process allows the creation of a thermally affected zone 11 with the substrate, ensuring good adhesion to the substrate, such as the first and second external surfaces 2a, 3a.

[0093] The EHLA laser deposition technique makes it possible to achieve a deposition speed of up to 200 m / min and a surface area rate of up to 500 cm² / min, which is 100 times faster than in the conventional Laser Cladding technique. Indeed, certain parameters such as the laser power or the powder flow rate are higher.

[0094] Unlike conventional Laser Cladding, in the EHLA technique, the particles are melted before coming into contact with the substrate, at approximately 1 mm from the substrate. The entire powder stream 10 converges towards a region 12 at a distance from the substrate. The particles present in the powder stream 10, thus melted, are then transported by the gas and fall into the melting basin 13. As the substrate is already heated by the laser 9, the thermally affected zone 11, which corresponds to a melting zone between a part of the projected powder and a part of the substrate, is thinner than in the Laser Cladding process, and the energy absorbed by the substrate is less.

[0095] The very thin, or even non-existent, thermally affected zone 11 obtained via the EHLA technique makes it possible, during the formation of the coating 6, not to deform the material of the brake disc 1, such as cast iron, on which the coating 6 is formed, and not to modify its properties, in particular its resistance to deformation properties.

[0096] Such a coating 6 obtained by the EHLA technique has optimized mechanical resistance properties, particularly against thermomechanical stresses and wear, which makes it possible to limit the emission of polluting particles by the brake disc 1 during braking as well as outside the braking phases of the motor vehicle.

[0097] The invention also relates to a method of manufacturing a brake disc as previously described, comprising the formation of the first layer 7 and the second layer 8 of the coating 6 by the very high speed laser material deposition technique known as EHLA.

[0098] Advantageously, the manufacturing process includes the formation of the coating 6 on the first friction track 4, and the formation of the coating 6 on the second friction track 5.

[0099] In the manufacturing process, the material of the first layer 7 and the material of the second layer 8 are sprayed in powder form.

[0100] The powder projected to form the first layer 7 comprises a steel having a chromium content of between 10 and 20% by mass relative to the total mass of the steel.

[0101] The powder projected to form the second layer 8 comprises steel, intended to form the matrix of the second layer 8 after projection, having a chromium content of between 10 and 20% by mass relative to the total mass of the steel.

[0102] The powder sprayed to form the second layer 8 also comprises a content of between 15 and 40% by volume of at least one carbide relative to the total volume of the second layer, the carbide intended to form reinforcements in the steel matrix after spraying being selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof, preferably selected from niobium carbide, titanium carbide or a mixture thereof;

[0103] The characteristics previously described for the first layer 7 apply to the powder intended to form the first layer 7.

[0104] The characteristics previously described for the second layer 7 apply to the powder intended to form the second layer 8.

[0105] Preferably, the particle size of the powder intended to form the first layer 7 and of the powder intended to form the second layer 8 is between 10 and 60 pm.

[0106] Preferably, the particles of the powder intended to form the first layer 7 and of the powder intended to form the second layer 8 are predominantly spherical in shape.

[0107] The material of the second layer 8 in powder form incorporates, preferably, the carbide(s) in cermet form.

[0108] Cermet is understood to mean a powder comprising ceramic reinforcements incorporated in a metallic phase.

[0109] According to one example, the cermet may comprise carbide particles inserted in a matrix comprising iron and chromium, thus forming agglomerates.

[0110] Preferably, the cermet matrix comprises predominantly iron and chromium.

[0111] By predominantly, we mean a matrix in which the sum of the iron and chromium contents represents a value greater than or equal to 50% by weight of the cermet.

[0112] Preferably, the step of forming the second layer 8 of the manufacturing process includes the use of cermets.

[0113] In other words, the powder material used to form the second layer 8 of the coating 6 incorporates the carbide(s) in the form of cermet.

[0114] The use of cermets makes it possible to achieve a regular deposit of constant thickness.

[0115] The integration of carbides in the form of spherical cermet in steel facilitates their deposition by projection.

[0116] Preferably, the manufacturing process includes a machining step carried out after the formation of the coating 6 in order to even out its surface which may be irregular and to adjust its thickness.

[0117] After machining, the thickness of the coating 6 is between 300 and 500 µm, preferably between 350 and 450 µm.

[0118] It may be foreseen that such a brake disc may be used in a transport vehicle other than a motor vehicle, and may be applied in particular to the aeronautical or railway field. Examples:

[0119] Example 1: Two-layer coating 430L + 30 vol% NbC by EHLA spray

[0120] The coating of Example 1 was formed on a GJL 150 lamellar graphite cast iron brake disc. The coating comprises a first layer disposed in contact The first layer is made of cast iron and 430L stainless steel. A second layer, placed on top of the first, consists of a 430L steel matrix and niobium carbide reinforcements. The niobium carbide content is 30% by volume of the total volume of the second layer.

[0121] The deposition of the first layer and the deposition of the second layer were carried out successively by projecting the material of the first layer and the second layer in powder form using the EHLA technique.

[0122] In particular, the second layer was formed by spraying a powder mixture comprising 430L steel powder and niobium carbide powder. The niobium carbide powder was sprayed in the form of cermet, i.e., comprising niobium carbide particles embedded in a matrix containing iron and chromium to form agglomerates. The cermet-type powder used incorporates 80% by weight of niobium carbide and 20% by weight of FeCr relative to the total weight of the cermet.

[0123] A machining step was carried out to rectify the thickness obtained after spraying. Given the irregular surface of the first layer, the coating obtained after machining has a thickness of between 350 and 400 µm.

[0124] The addition of niobium carbide to 430L steel increases the hardness of the second layer relative to the first layer. The resulting average hardness of the second layer is 485 HV1.

[0125] Thermal damage tests and particle emission measurement during braking showed the absence of cracks and the reduction of particle emissions.

[0126] The coated brake disc obtained by the EHLA technique therefore makes it possible to obtain excellent capacities obtained in terms of resistance to thermal damage and in terms of particle emission during braking.

[0127] Example 2: Two-layer coating 430L + 20 vol% TiC by EHLA spray

[0128] The coating of Example 2 was also formed on a cast iron brake disc at GJL 150 lamellar graphite. The coating comprises a first layer, in contact with the GJL cast iron, made of 430L stainless steel. A second layer, applied over the first, consists of a 430L steel matrix and titanium carbide reinforcements. The titanium carbide content is 20% by volume of the total volume of the second layer.

[0129] The deposition of the first layer and the deposition of the second layer were carried out successively by powder spraying using the EHLA technique.

[0130] In particular, the second layer was formed by spraying a powder mixture comprising 430L steel powder and titanium carbide powder. The titanium carbide powder was sprayed in the form of cermet, i.e. comprising titanium carbide particles embedded in a matrix containing iron and chromium to form agglomerates. The cermet-type powder used incorporates 70% by mass of titanium carbide and 30% by mass of FeCr relative to the total mass of the cermet.

[0131] Similar to Example 1, a machining step was performed to correct the thickness obtained after spraying. The coating obtained after machining has a thickness between 440 and 470 µm.

[0132] Thermal damage tests and particle emission measurement during braking showed the absence of cracks and the reduction of particle emissions.

[0133] The coated brake disc obtained by the EHLA technique therefore makes it possible to obtain excellent capacities obtained in terms of resistance to thermal damage and in terms of particle emission during braking.

Claims

Demands

1. Motor vehicle brake disc comprising at least one external surface (2a, 3a) having a coating (6), the coating (6) comprising: a first layer (7) disposed at least partially on the external surface (2a, 3a), the first layer (7) comprising a steel having a chromium content of between 10 and 20% by mass relative to the total mass of the steel;a second layer (8) disposed on the first layer (7), the second layer (8) comprising a steel matrix having a chromium content of between 10 and 20% by mass relative to the total mass of the steel, and a content of between 15 and 40% by volume of at least one carbide relative to the total volume of the second layer, the carbide being selected from the following compounds: silicon carbide, chromium carbide, tungsten carbide, niobium carbide, titanium carbide or a mixture thereof, preferably selected from niobium carbide, titanium carbide or a mixture thereof; the coating (6) being obtained by means of an ultra-high-speed laser deposition technique known as EHLA.

2. Brake disc according to claim 1, wherein the steel of the first layer (7) and / or the steel of the second layer (8) is ferritic steel, preferably ferritic steel consisting of a chromium content of between 16 and 18% by mass, a silicon content of less than or equal to 1% by mass, a nickel content of less than or equal to 0.6% by mass, a manganese content of less than or equal to 1% by mass, a carbon content of less than or equal to 0.08% by mass, a molybdenum content of less than or equal to 1% by mass, a phosphorus content of less than or equal to 0.045% by mass, a sulfur content of less than or equal to 0.03% by mass, a titanium content of less than or equal to 0.01% by mass, optionally other alloying elements such as copper, vanadium, niobium, or tin, the remainder being iron as well as inevitable impurities.

3. Brake disc according to claim 1 or 2, wherein the second layer (8) comprises a titanium carbide content of between 15 and 25% by volume, preferably between 17 and 23% by volume, preferably still between 19 and 21% by volume, relative to the total volume of the second layer (8).

4. Brake disc according to claim 1 or 2, wherein the second layer (8) comprises a niobium carbide content of between 25 and 35% by volume, preferably between 27 and 33% by volume, preferably still between 29 and 31% by volume, relative to the total volume of the second layer (8).

5. Brake disc according to claim 1 or 2, wherein the second layer (8) comprises a mixture of carbides, the content of each carbide in the mixture of carbides being between 5 and 20% by volume, preferably between 5 and 10% by volume, relative to the total volume of the second layer (8).

6. Brake disc according to claim 5, wherein the second layer (8) comprises a mixture of niobium carbide and titanium carbide, the niobium carbide content being between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer, and a titanium carbide content being between 5 and 20% by volume, preferably between 5 and 10% by volume relative to the total volume of the second layer (8).

7. Brake disc according to any one of the preceding claims, wherein the material of the brake disc (1) on which the coating (6) is disposed is cast iron, preferably lamellar graphite cast iron.

8. Brake disc according to any one of the preceding claims, comprising first and second opposing faces (2, 3) respectively having first and second external surfaces (2a, 3a), each of the first and second external surfaces (2a, 3a) comprising a friction track (4, 5) intended to cooperate with a brake pad, the coating (6) being disposed at least partially on the friction tracks (4, 5), preferably only disposed on the friction tracks (4, 5).

9. A method for manufacturing a brake disc according to any one of the preceding claims, comprising the formation of the first layer (7) and the second layer (8) of the coating (6) by an ultra-high-speed laser material deposition technique known as EHLA.

10. A manufacturing process according to claim 9, wherein the step of forming the second layer (8) of the manufacturing process

11. includes the use of cermets. Motor vehicle comprising at least one brake disc (1) according to any one of claims 1 to 8.

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