Coated grey cast iron component and manufacturing process

Abstract

Component with tribologically stressed surfaces, comprising a grey cast iron substrate (3) and at least one cover layer (1), wherein between the substrate (3) and the at least one cover layer (1) directly on the grey cast iron substrate (3) a surface layer (2) is formed which has nitride-, carbide- and oxide-containing layers, wherein an oxide-containing layer forms the uppermost layer of the surface layer (2), wherein the cover layer (1) consists of a cermet material comprising a metallic matrix and an oxide ceramic component distributed therein, which makes up 30 to 70 wt.% of the cermet material.

Description

[0001] The invention relates to a component made of a grey cast iron substrate with a cover layer, in particular a brake disc of a motor vehicle, and a method for its production.

[0002] It is known from the state of the art to improve the corrosion and wear behavior of iron-based materials by forming a closed oxide layer after nitriding or nitrocarburizing in gaseous or liquid media.

[0003] Brake discs have friction rings that form a tribological system with the brake pads. During braking, when the stationary brake pads come into contact with the rotating friction rings, the friction rings of the brake discs heat up due to friction. The braking effect depends on the condition and surface finish of the friction ring. The increased temperature of the brake disc resulting from braking, possibly in combination with corrosive media such as water and road salt, leads to or accelerates corrosion on the friction rings. For this reason, brake discs are often coated with a corrosion protection layer on the friction rings.However, if this has cracks that extend to the brake disc base body, for example due to different thermal expansion coefficients, or if the cover layer and base body have different electrochemical voltage potentials, corrosion of the base body under the cover layer (corrosive infiltration) can occur, which leads to delamination of the coated base body and thus to restrictions or even loss of braking effect.

[0004] In order to improve the resistance of the brake discs to corrosion and oxidation, especially at elevated temperatures, the friction surfaces of brake discs made of iron-based material are provided with a corrosion protection layer by subjecting them to a nitrocarburizing surface treatment and subsequent oxidative post-treatment.

[0005] For example, DE 10 2007 027 933 B4 discloses a method for nitrocarburizing brake rotors of a motor vehicle. 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. The surface of the brake rotor then has a compound layer and an underlying diffusion layer. An oxide layer containing Fe3O4 is present on the surface of the compound layer; beneath this, the compound layer consists primarily of ε-iron nitride, Fe3N, and a smaller proportion of γ'-iron nitride, Fe4N. The diffusion layer contains a lower concentration of diffused nitrogen in the iron-based material than in the compound layer.

[0006] DE 10 2011 053 253 A1 describes a brake disc consisting of a carrier part and a friction ring, which are connected to each other via connecting elements made of steel material. The connecting elements have a corrosion protection layer, at least at the end sections, which consists of a diffusion layer, an overlying bonding layer containing iron carbonitrides, and an oxide layer on top of it.

[0007] DE 195 25 182 A1 discloses a gas process for producing corrosion and wear protection coatings on iron-based materials that avoids the disadvantages of salt bath processes with regard to environmental impact and the resulting surface topography – the surfaces produced in the salt bath process are rough and require post-treatment. Nitrocarburization is initially performed in a normal-pressure gas process, forming the bonding layer from iron carbonitrides. The surface of the bonding layer is then activated in a plasma-assisted vacuum process, before a continuous and uniform oxide layer is formed by oxidation in the normal-pressure gas process.

[0008] The described process for producing a corrosion and wear protection layer on low-alloy steels is known under the name IONIT OX <tm>from Sulzer Metco, Bergisch Gladbach (http: / / www.sulzer.com / de / Products-and-Services / Coating-Services / Plasma-Heat-Treatment / Processes / IONIT-OX). Further information on areas of application, such as brake discs, and the advantages of the process are described in the online brochures: "Chassis Technology - Surface Solutions for Efficient Use" (https: / / www.sulzer.com / de / / media / Documents / ProductsAndServices / Coating_Services / DLC_Coatings / Brochures / Chassis_V1.pdf) and "Surface Solutions for the Efficient Construction of Chassis, Brakes, Drives and Engines" (http: / / www.sulzer.com / de / / media / Documents / ProductsAndServices / Coating_Equipment / Pla sma_Heat_Treatment / Brochures / Surface_Solutions_Automotive_V1.pdf).

[0009] EP 2 394 072 B1 describes a method for producing a gray cast iron brake disc for a vehicle, the friction surfaces of which are post-treated by carburizing, carbonitriding, case hardening, gas nitriding, oxide nitriding, gas nitrocarburizing, plasma nitriding, plasma oxidation, boronizing, plasma carborizing, or plasma boronizing. Before post-treatment, the friction surfaces can be coated with a layer of tungsten carbide, chromium carbide, and nickel, or with a layer of tungsten carbide, cobalt, chromium, and nickel.

[0010] DE 10 2011 122 308 A1 also discloses a coated component or brake disc, wherein an intermediate layer is formed between the substrate and the cover layer by phosphating, nitriding, boronizing, sputtering, bainitriding, carburizing, carbonitriding, plasma nitrocarburizing, anodizing, a chemical nickel dispersion, a thermal process, a chemical process, physical vapor deposition, and / or chemical vapor deposition. The teaching of this document is formulated such that, in the case of nitriding or carbonitriding, the resulting layering also forms the outermost part of the intermediate layer.

[0011] From DE 10 2004 016 098 A1 a brake disc with a non-specific wear protection layer is known, which lies on a galvanically applied intermediate layer.

[0012] From DE 10 2009 008 105 B4 a brake disc is known which carries a special wear protection layer which is applied to the brake disc without an intermediate layer.

[0013] DE 10 2011 129 989 B3 describes a special wear protection layer that is sprayed directly onto the brake disc without an intermediate layer.

[0014] Based on this prior art, it is the object of the present invention to provide a further improved component, such as a brake disc made of grey cast iron, which is protected against corrosion and wear and in which crack propagation in the cover layer to the substrate as well as corrosive infiltration of the cover layer, which leads to delamination and even to the total failure of the component, is prevented or delayed.

[0015] This object is achieved by a component having the features of claim 1.

[0016] The object of producing such a component is achieved by a method having the features of claim 9.

[0017] Further developments of the component and the method are set out in the respective subclaims.

[0018] A component according to the invention with tribologically stressed surfaces comprises a gray cast iron substrate with a cover layer, which may optionally consist of multiple cover layer layers. A surface layer comprising nitride-, carbide-, and oxide-containing layers is formed directly on the substrate below the cover layer. This surface layer is formed according to the invention by nitrocarburizing and oxidation. To improve corrosion and crack resistance as well as wear protection, the cover layer consists of a cermet material consisting of a metallic matrix and a ceramic component distributed therein, which makes up 30 to 70 wt.% of the cermet material. The cover layer is designed, in particular, as a friction layer for a brake disc. "Cermet" refers to very hard and wear-resistant composite materials made of ceramic materials in a metallic matrix with high thermal shock and oxidation resistance.

[0019] The top layer preferably only partially covers the component. The top layer is applied at least to functional surfaces of the component. A preferred functional surface is the friction surface of a brake disc.

[0020] The cermet top layer, combined with the hardened surface layer formed by nitrocarburizing and oxidation as an electrochemical barrier, gives the component significantly improved corrosion and crack resistance. This significantly delays corrosive infiltration, which could lead to total failure of the coating system through delamination, thus significantly extending the service life and lifetime of the coating system or the component itself—for example, a vehicle's brake disc.

[0021] The structure of the surface layer is of particular importance for the corrosion protection of the grey cast iron substrate and the adhesion of the top layer.

[0022] The surface layer on the gray cast iron substrate is formed by several merging layers or layers. The bottom layer, with a thickness of 100 to 800 µm, is a diffusion zone in which the gray cast iron material contains dissolved nitrogen, special nitrides, carbides, and nitride precipitates. This layer transitions into a compound layer with a thickness of 2 to 20 µm, which contains epsilon nitride or carbonitride, gamma nitride, and special nitrides. The top layer, with a thickness of 1 to 3 µm, is essentially formed by iron oxide, particularly Fe3O4.

[0023] According to the invention, high-alloy steels or Cr-nickel alloys with a Cr content above 15 wt.% are used as the metallic matrix of the wear-resistant top layer or cermet top layer.

[0024] High-alloy CrNiMo steels or NiCrMo alloys are particularly suitable.

[0025] A suitable CrNiMo steel is Fe28Cr16Ni4.5Mol.5Si1.75C, which has a composition of 28 wt% chromium, 16 wt% nickel, 4.5 wt% molybdenum, 1.5 wt% silicon, 1.75 wt% carbon, the remainder iron.

[0026] Suitable NiCrMo alloys may have a composition of 20 to 23 wt.% chromium, up to 5 wt.% iron, 8 to 10 wt.% molybdenum, 3.15 to 4.15 wt.% niobium and tantalum in total, the weight fraction supplementing 100% (balance) nickel; particularly preferably, the alloy composition may have 21.5 wt.% chromium, 2.5 wt.% iron, 9.0 wt.% molybdenum, 3.7 wt.% niobium and tantalum in total, the balance nickel.

[0027] A particularly suitable austenitic stainless steel is 1.4404 or 316L, which contains 16-18.5 wt% Cr, 10-14 wt% Ni and 2-2.5 wt% Mo.

[0028] The ceramic component of the cermet material of the cover layer comprises oxide ceramics selected from Al2O3, TiO2, ZrO2 and MgAl2O4 (spinel) and combinations thereof.

[0029] The adhesion of the oxide ceramics is particularly favored by the top layer of the surface layer on the gray cast iron substrate made of Fe3O4.

[0030] In one embodiment, the ceramic component may comprise Al2O3 and at least one further oxide ceramic selected from TiO2, ZrO2, and MgAl2O4, with Al2O3 accounting for 60 to 90 wt.% of the total ceramic component. A particularly preferred ceramic composition consists of 97 wt.% Al2O3 and 3 wt.% TiO2.

[0031] The ceramic content within the cermet material is preferably 30 to 70 wt.%.

[0032] The surface layer on the gray cast iron substrate surface comprises an oxide layer over a nitrocarburized compound layer, adjacent to a diffusion layer in which the concentration of gases diffused into the substrate is lower than in the compound layer. The compound layer predominantly contains ε-iron nitride, as well as other nitrides and carbides, and the oxide layer predominantly contains iron oxide. The thickness of the diffusion layer ranges from 0.1 to 0.8 mm, that of the compound layer from 2 to 30 µm, and that of the oxide layer from 1 to 5 µm.

[0033] The surface coating can be limited to the functional surface of the component. Preferably, it is applied to the entire component surface, as this provides the entire component with a corrosion protection layer. In particular, the surface coating is also applied to the surfaces of ventilation ducts or through-holes of an internally ventilated and perforated brake disc. This provides effective corrosion protection for the entire brake disc and prevents corrosion products from penetrating the surface layer from through-holes or perforations.

[0034] In a further embodiment of the invention, an intermediate layer is provided between the cover layer and the surface layer. This intermediate layer consists of a nickel-based alloy, preferably a nickel-chromium alloy, or of the matrix metal of the cermet material without the ceramic component. This additional intermediate layer can have a layer thickness in the range of 30 to 120 µm. The intermediate layer serves to compensate for the different thermal expansion coefficients of the gray cast iron substrate and the cermet cover layer, essentially as an elastic compensation.

[0035] The thickness of the cermet top layer ranges from 100 to 500 µm. Preferably, the top layer and, accordingly, the surface or intermediate layers can be provided only on tribologically stressed surfaces of the component, while the substrate is present on the surface or other coatings can be present in other areas of the component.

[0036] In order to improve the bond between the cover layer and the substrate, the surface of the substrate and thus the surface or intermediate layers in the areas covered by the cover layer can be mechanically roughened or profiled so that the cover layer interlocks with the substrate.

[0037] The component according to the invention, which is significantly improved in terms of wear and corrosion resistance by the cover layer and the surface and, optionally, intermediate layers, can be a brake disc for a motor vehicle, with the cover layer being applied to the friction surfaces of the brake disc. In addition to the improved wear and corrosion resistance, the cermet cover layer also provides improved tribological properties for the brake disc-brake pad friction system.

[0038] A method according to the invention for producing a component according to the invention first comprises producing the component substrate from gray cast iron, for example, casting a brake disc base body from a gray cast iron alloy. The substrate surface is then subjected to nitrocarburization in a gas, plasma, or salt bath process, at least on the surface areas that form tribologically stressed surfaces of the component, and is oxidized by anodic or plasma oxidation, forming the surface layer. A preferred hardening process comprises nitrocarburization, plasma activation, and oxidation of the substrate surface. For the cover layer, a cermet material is provided consisting of a metallic matrix and a ceramic component distributed therein, which makes up 30 to 70 wt.% of the cermet material.Preferably, the components of the cermet material are provided as powder and only combined to form the finished cermet material upon application to the surface layer. The cermet material is applied to the surface layer, thus forming the cover layer. The cermet material is preferably applied by thermal spraying, in particular powder spraying, or by spray compaction.

[0039] Before nitrocarburizing and oxidizing, the surfaces of the substrate, which form the tribologically stressed surfaces of the component, can be mechanically roughened or profiled.

[0040] Alternatively or in addition to profiling the substrate surface, a nickel-based alloy or the pure matrix metal can be applied to the surface layer after nitrocarburizing and oxidizing the substrate surface, thus forming an additional intermediate layer as wear protection and, if necessary, to support the adhesion of the top layer to the surface layer.

[0041] The nickel-based alloy or matrix metal can also be applied by thermal spraying. Nickel or nickel alloys are preferably applied electroplating.

[0042] These and other advantages are set forth in the following description with reference to the accompanying figures.

[0043] Reference to the figures in the description serves to facilitate understanding of the subject matter. The figures are merely a schematic representation of an embodiment of the invention.

[0044] Showing: Fig. 1 a cross-sectional view through a section of a component according to the invention made of grey cast iron substrate with surface layer and cover layer, Fig. 2 a cross-sectional view through a section of a component according to the invention made of grey cast iron substrate with hardened surface layer, a further nickel-based intermediate layer and cover layer, Fig. 3 a microscopic micrograph through a section of a component according to the invention made of grey cast iron substrate with a profiled surface and hardened surface layer, a further nickel-based intermediate layer and cover layer, Fig. 4 a cross-sectional view through a section of a component according to the invention made of a grey cast iron substrate with the surface layer formed from a diffusion layer, a connecting layer and an oxide layer, a further nickel-based intermediate layer and a cover layer.

[0045] The invention relates to a component with a gray cast iron base body, the corrosion and wear properties of which are improved by a hardened surface layer and a cover layer applied thereon, and optionally also by additional layers. These layers prevent or reduce, for example, the propagation of cracks that may occur on the surface of the component during operation. By preventing crack propagation into the gray cast iron substrate, corrosive infiltration of the layers is also effectively prevented, so that failure of the component, for example due to delamination, does not occur or occurs much later.

[0046] Fig. Figure 1 schematically shows a cross-section through a component section. On the surface of the gray cast iron substrate 3, which forms the base body of the component, a hardened surface layer 2 is formed by nitrocarburizing and oxidation, to which a cover layer 1 is applied. The cover layer 1 consists of a cermet material comprising a metallic matrix and a ceramic component distributed therein, which accounts for 30 to 70 wt.% of the cermet material.

[0047] Fig. 2 shows an alternatively designed component which has an additional intermediate layer 4 made of a nickel-based alloy, preferably a corrosion-resistant and high-temperature-resistant nickel-chromium alloy, between the hardened surface layer 2 and the cover layer 1.

[0048] The photographic microscope image in Fig. 3 shows a substrate 3 with a profiled surface. The hardened surface layer 2 is present on the substrate surface with a layer thickness of approximately 30 µm bonding layer and 3 µm oxide layer and is indicated by the dashed line. In this exemplary embodiment, a nickel-based intermediate layer 4 with an average layer thickness of approximately 100 µm is applied to the profiled substrate 3 or the surface layer 2. As can be seen in the image, the layer thickness of the intermediate layer 4 varies due to the profiled substrate surface. The cover layer 1 made of cermet has an average thickness of approximately 350 µm. Variations in the layer thickness also result here from the profiled substrate surface, which, however, advantageously ensures a better bond between the cover layer 1 and the substrate 3 coated with the intermediate layer 4 due to this interlocking effect.

[0049] The following is based on Fig. 4, in which the layers of a component according to the invention are outlined in more detail in an embodiment with an additional intermediate layer 4, explains the production of a component according to the invention.

[0050] A component according to the invention has on the gray cast iron substrate 3, which forms the cast base body, the hardened surface layer 2, which is preferably formed by nitrocarburizing, plasma activation and oxidation according to the IONIT OX™ process, but optionally also by other nitriding, carburizing, nitrocarburizing and oxidation processes. Optionally (in Fig. 4 not shown), the substrate surface can be mechanically profiled beforehand. The surface layer 2 is composed of a diffusion layer 21, a compound layer 22, and an oxide layer 23, starting from the substrate 3. During nitrocarburization, nitrogen and carbon penetrate the substrate surface, with predominantly ε-iron nitride or carbonitride, and to a lesser extent γ'-iron nitride and special nitrides, being formed in the compound layer 22, whose layer thickness is in a range of 2 to 30 µm. The diffusion layer 21 extends into the substrate 3 below the compound layer 22. This diffusion layer has lower concentrations of diffused nitrogen and carbon than in the compound layer 22, and in which nitrogen is present in "solution" in the substrate structure alongside special nitrides, carbides, and nitride precipitates.The thickness of the diffusion layer is in the range of 0.1 to 0.8 mm, depending on the treatment conditions and the substrate properties.

[0051] The surface of the connecting layer 22 is oxidized after plasma activation, so that a largely closed oxide layer 23 made of Fe3O4 with a layer thickness in the range of 1 to 5 µm is formed on the connecting layer 22, which has a defined pore structure.

[0052] To build up the layer structure Fig. 4, an intermediate layer 4 made of a nickel-based alloy or the matrix metal is applied to the oxide layer 23 before the cermet material is applied to form the cover layer 1. The intermediate layer 4 can have a layer thickness in the range of 30 to 120 µm and the cover layer 1 can have a layer thickness in the range of 100 to 500 µm.

[0053] Between the intermediate layer 4 and the oxide layer 23—in embodiments without an intermediate layer 4, correspondingly between the cermet cover layer 1 and the oxide layer 23—there is a mixing zone 11 in which the iron oxide of the oxide layer 23 is mixed with the nickel-based alloy or the matrix metal of the intermediate layer 4 (or with the matrix metal of the cover layer 1). If the intermediate layer 4 consists of a nickel-based alloy that differs from the matrix metal, then a mixing zone 11 also exists between the cover layer 1 and the intermediate layer 4. The thickness of the mixing zone 11 can vary depending on the application method and application parameters.

[0054] Both the application of the nickel-based alloy or matrix metal to form the intermediate layer 4 and the application of the cermet material to form the cover layer 1 can be carried out by thermal spraying.

[0055] The cover layer 1 and the underlying layers 2, 4 can be limited to tribologically stressed surfaces of the component, ie in the case of a brake disc as a component to the friction surfaces of a brake disc.

[0056] The matrix metal can be a high-alloy CrNiMo steel or a NiCrMo alloy. Nickel-based, preferably NiCr alloys, or pure matrix metal without a ceramic component can be used for the additional intermediate layer.

[0057] A CrNiMo steel suitable for forming the metallic matrix of the cover layer has the composition Fe 28Cr 16 Ni 4.5 Mo 1.5 Si 1.75 C. Suitable NiCrMo alloys include compositions of Ni 20-23Cr < 5Fe 8-10Mo 3.15-4.15Nb(+Ta) (InconelTM 625, Special Metals Corporation, Huntington, West Virginia, USA), with Ni 21.5Cr 2.5Fe 9.0Mo 3.7 (Nb + Ta) being particularly preferred.

[0058] Other nickel-based alloys, especially NiCr alloys, can also be used as materials for forming the intermediate layer.

[0059] The ceramic component of the cover layer 1 comprises oxide ceramics such as Al2O3, TiO2, ZrO2, and MgAl2O4 (spinel). These can be selected individually or in combination as the reinforcing ceramic component of the cermet. For example, in addition to Al2O3 as the main component, the ceramic component can have at least one further oxide ceramic as a secondary component, which is selected from the group comprising TiO2, ZrO2, and MgAl2O4. The proportion of Al2O3 in the total ceramic component, the proportion of which in the cermet material ranges from 30 to 97 wt.% of the cermet material, can amount to 60 to 90 wt.%. The further oxide ceramics TiO2, ZrO2, and / or MgAl2O4 are then present in a proportion of 10 to 40 wt.% of the total ceramic component. Preferably, the proportion of Al2O3 in the total ceramic component is in the range of 75 to 85 wt.%, preferably 80 wt.%.

[0060] The top layer of the cermet material, applied, for example, by thermal spraying, has a porosity of less than 5% and a microhardness between 300 HV.03 and 1000 HV.03.< / tm>

Claims

[1] Component with tribologically stressed surfaces, comprising a grey cast iron substrate (3) and at least one cover layer (1), wherein between the substrate (3) and the at least one cover layer (1) directly on the grey cast iron substrate (3) a surface layer (2) is formed which has nitride-, carbide- and oxide-containing layers, wherein an oxide-containing layer forms the uppermost layer of the surface layer (2), wherein the cover layer (1) consists of a cermet material comprising a metallic matrix and an oxide ceramic component distributed therein, which makes up 30 to 70 wt.% of the cermet material. [2] Component according to claim 1, characterized bythat the metallic matrix of the cermet material is a high-alloy CrNiMo steel, which preferably has a composition comprising 28 wt.% chromium, 16 wt.% nickel, 4.5 wt.% molybdenum, 1.5 wt.% silicon, 1.75 wt.% carbon, the remainder being 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 wt.% niobium and tantalum in total, the remainder being nickel. [3] Component according to claim 1 or 2, characterized by that the ceramic component comprises oxide ceramics selected from Al2O3, TiO2, ZrO2 and MgAl2O4 and combinations thereof. [4] Component according to claim 1, 2 or 3, characterized by that the ceramic component comprises Al2O3 and at least one further oxide ceramic selected from the group comprising TiO2, ZrO2, MgAl2O4, wherein Al2O3 accounts for a proportion of 60 to 97 wt.% of the total ceramic component. [5] Component according to at least one of claims 1 to 4, characterized by that the surface layer (2), starting from the substrate (3), has a diffusion layer (21), a nitride- and carbide-containing connecting layer (22) and an oxide layer (23), wherein the diffusion layer (21) has a layer thickness of 0.1 to 0.8 mm, the connecting layer (22) has a layer thickness of 2 to 30 µm and the oxide layer (23) has a layer thickness of 1 to 5 µm. [6] Component according to at least one of claims 1 to 5, characterized by that an intermediate layer (4) is provided between the cover layer (1) and the surface layer (2), which intermediate layer consists of a nickel-based alloy, preferably a nickel-chromium alloy, or of the metallic matrix, wherein the intermediate layer (4) made of the nickel-based alloy or the matrix metal has a layer thickness of 30 to 120 µm. [7] Component according to at least one of claims 1 to 6, characterized bythat - the cover layer (1) has a layer thickness of 100 to 500 µm, and / or - the cover layer (1) is provided on tribologically stressed surfaces of the component, and / or - the surface of the substrate (3) is roughened in the areas covered by the cover layer (1). [8] Component according to at least one of claims 1 to 7, characterized by that the component is a brake disc for a motor vehicle, the surface layer is applied substantially to the entire component surface and the cover layer (1) is applied to the friction surfaces of the brake disc. [9] Method for producing a component according to at least one of claims 1 to 8, comprising the steps: - Production of the grey cast iron substrate (3), - forming the surface layer of the substrate, at least on the surfaces forming the tribologically stressed areas of the component, by nitrocarburising in a gas, plasma or salt bath process, - Oxidation by anodic oxidation or plasma oxidation, which forms the top layer of the surface layer, - Providing a cermet material comprising a metallic matrix and a ceramic component distributed therein, which constitutes 30 to 70 wt.% of the cermet material, and - Applying the cermet material to the surface layer (2) and forming the cover layer (3). [10] A method according to claim 9, wherein said forming of the surface layer is carried out by nitrocarburizing, plasma activation and oxidation. [11] Method according to claim 9 or 10, comprising at least one of the steps: before nitrocarburizing and oxidizing - mechanically roughening the surfaces of the substrate (3), at least on the surfaces that form the tribologically stressed surfaces of the component, and / or after nitrocarburizing and oxidation - Applying a nickel-based alloy or the matrix metal to the surface layer (2), thereby forming an intermediate layer (4). [12] Method according to claim 11, wherein the application of the cermet material to form the cover layer (1) and / or the application of the nickel-based alloy or the matrix metal to form the further intermediate layer (4) is carried out by thermal spraying.

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