Workpiece with a coating system

Abstract

The invention relates to a workpiece (1) with a coating system (2), wherein the coating system (2) is applied to a base body (3) and comprises at least two layers (4, 5), wherein the first layer (4) is applied directly adjacent to the base body (3) and is formed from an iron-based alloy (6), and wherein the second layer (5) is applied to the first layer (4) and is formed as a matrix alloy (7) with an iron-based alloy (6) as a matrix and hard material particles (8) embedded therein, wherein a residual compressive stress (9) is present in the first layer (4), and wherein a first grain group (10) of the hard material particles (8) with a grain size of 2 µm to 60 µm is embedded in the second layer (5). With the coated workpiece proposed here, crack formation can be sufficiently prevented.

Description

The invention relates to a workpiece with a coating system, and to a method for coating a base body of such a workpiece.In the industry, for example the automobile industry, the trade-off of quality criteria of components under high cost awareness is an ever-increasing challenge. In addition, questions of sustainability in this equation also gain relevance. In the field of brake disks, or other coated parts, subjected to high stresses, this problem becomes particularly evident.Brake disks are known in the prior art, for example, as cost-effective components, made entirely or partially from gray cast iron. However, a problem with cast brake disks is that they tend to corrode and exhibit inadequate abrasion resistance, leading to a contribution to increased particulate loading. For example, braking of uncoated cast brake disks causes about 15% of the total particulate matter emission of a vehicle. These negative properties can be reduced by coating the brake disk base bodies. Laser coating methods have generally become established in comparison with paint coatings because, for example, a functional layer can be produced as a result, which achieves a higher abrasion resistance, an improved corrosion protection and a reduction in the fine dust emission.A method known in the prior art for coating base bodies, for example brake disks, is flame spraying. Here, a welding filler material of wire or powder is introduced into a nozzle. When supplying a powdered welding filler material, the powder material used is conveyed uniformly from a powder container and is guided by a conveying gas stream through the burner nozzle to the burner flame. This ensures that molten or partly molten particles additionally adhere to the surface to be coated in an accelerated manner by the combustion flame. Flame spraying is a comparatively simple and cost-effective method, but the resulting coatings can have a relatively high porosity, lack a melt-metallurgical bond to the base body and high gas consumption.An alternative is laser build-up welding [LA], in which, for example, a lower porosity can be achieved with reduced gas consumption. The LA is a welding method which melts by means of laser radiation the welding filler material used, supplied in powder form or wire form. When supplying a powdered welding filler material, this powdered material is guided to a processing point by means of carrier gas under a protective gas atmosphere. The processing point is aligned with the base body surface. A laser beam is focused on the processing point and melts the substrate as well as powder material passing through the processing point. Unmelted powder particles of the powder material are completely melted in the melt bath. The powder nozzle is moved over the surface by means of displaceable axes and thereby generates weld beads. A coating is formed which consists essentially (i.e. under technical tolerance completely apart from a transition region, the so-called mixing zone) of the powder material. As a result, it is possible, for example, to infer the composition of the powder material directly even in material investigations on the finished coating. Under the coating is the mixing zone which consists of additive material and substrate material. The molten powder material collects over the mixing zone and forms the coating system.A person skilled in the art will immediately appreciate that a melt-metallurgical bond is formed independently of the layer thickness and / or number of layers, wherein this produces a technical improvement to, for example, thermally sprayed layers. The melt-metallurgical bond results in a mixture between the coating and the substrate. However, because the mixing zone is minimal in the LA compared to other welding methods, the coating material can be correspondingly concluded at the coating.High-speed laser deposition welding [HVLA: High-Velocity Laser Application] has emerged from the LA. In order to achieve higher feed speeds than in the case of LA, the welding filler material, provided as powder, is melted or melted by the laser energy already before it arrives on the substrate, that is to say above the substrate surface. This is achieved by crossing the powder streams to be melted in a so-called powder focus one or more millimeters above the substrate surface. It should be noted that the HVLA is preferably implemented with the welding device in the earth's gravity field above the substrate. However, this may vary in some applications. Above means therefore at least only at a distance from the substrate surface. A laser beam is superimposed on the powder focus, so that powder particles pass through the laser beam and thereby shadow it. As a result, not all the energy of the laser reaches the surface of the substrate. The ratio of the total laser power [Ll] to that of the laser power reaching the substrate is usually calculated as transmittance by the skilled person. By setting various process parameters and the resulting transmittance, a coating as a melt-metallurgical composite can be achieved by means of HVLA.A specific HVLA method is described (referred to there as extreme high-speed laser deposition welding [EHLA]), for example, in Schopphoven et. al. ("Experimental and model theoretical investigations on extreme high-speed laser deposition welding", dissertation at the Fraunhofer Institute for Laser Technology ILT, 2019, published online on the Internet pages of the university library), and DE 10 2011 100 456 A1.Documents WO 2021 / 007 209 A1 and WO 2021 / 126 518 A1 disclose coatings.All solutions known at present are based on the problem that crack formation and thus increased corrosion and fine dust formation can occur in use in a brake disc. The crack formation starts from the outer surface and continues inwardly partly as far as into the base body. Deep cracks can lead to corrosion-related detachment of the coating.Proceeding from this, the object of the present invention is to overcome at least partially the disadvantages known from the prior art. The features according to the invention are evident from the independent claims, for which advantageous embodiments are shown in the dependent claims. The features of the claims can be combined in any technically expedient manner, wherein the explanations from the following description and features from the figures, which comprise supplementary configurations of the invention, can also be used for this purpose.The invention relates to a workpiece having a coating system, wherein the coating system is applied to a base body and comprises at least two layers, wherein the first layer is applied directly adjacent to the base body and is formed from an iron-based alloy, and wherein the second layer is applied to the first layer and is formed as a matrix alloy having an iron-based alloy as a matrix and hard material particles embedded therein, wherein a residual compressive stress is present in the first layer, and wherein a first grain group of the hard material particles having a grain size of 2 μm to 60 μm is embedded in the second layer.Ordinal numbers used in the preceding and following description, unless expressly stated to the contrary, serve only for the clear distinguishability and do not represent an order or ranking of the designated components. An ordinal number greater than one does not require that a further such component must necessarily be present.The base body proposed here is particularly suitable for the use of a frictional load on the outermost layer, which is therefore also referred to here as a friction layer. The base body is particularly suitable for use as a brake disc. The thermal and / or cyclic loading leads to different thermal expansion in the materials used in the base body and the layers. This promotes crack formation. However, there are also other fields of application and causes of such crack formation.The base body is formed, for example, from a gray cast iron, preferably lamellar gray cast iron. Such a gray cast body has a high heat capacity and is therefore particularly suitable for high short-term (thermal) loads. At the same time, a gray cast iron body usually has an outer surface with a poor coefficient of friction and a low friction resistance, i.e. a tendency toward fine dust formation, and a high susceptibility to corrosion. A further advantage of a gray cast iron body is the good casting properties and low-cost manufacturing ability for mass production. Alternatively, the base body consists of steel and is preferably cast.In order to make use of these positive properties and at the same time to achieve a high corrosion resistance and, if appropriate, good friction resistance, it is proposed here that a coating be provided which is applied at least in the region of a load (for example the frictional engagement of a brake pad).It is proposed here that, in a preferred embodiment, a two-layer system is formed. Alternatively, at least one further layer is provided.The first layer is applied directly on the outer surface of the base body and is therefore also referred to as an adhesive layer. In a preferred embodiment, the first layer comprises no added, particularly preferably also no (or in no technically relevant amount) agglomerated, hard material particles. Agglomerated hard material particles are hard material particles which (usually very small, for example less than 10 μm) contain hard material particles which are hardly processable (for example conveyable) on account of their (melt-prone) material and / or their grain size. Therefore, these hard material particles are combined with a (preferably metallic) binder (for example an iron-chromium alloy [FeCr]) to form an agglomerated, i.e. enlarged, (mixed) particle (for example 15 μm to 53 μm or 45 μm to 90 μm). These mixed particles, i.e. agglomerated hard material particles, are thus easier to process in the manufacturing process, for example are reliably conveyable and / or at least less susceptible to melting or melting.In an advantageous embodiment (with iron [Fe] as the remainder (with unavoidable impurities) the iron-based alloy comprises the following chemical components:carbon [C] between 0% by weight and 0.07% by weight, preferably not more than 0.03% by weight;silicon [Si] between 0% by weight and 1% by weight;manganese [Mn] between 0% and 2% by weight;phosphorus [P] between 0% by weight and 0.045% by weight;sulfur [S] between 0% by weight and 0.03% by weight, preferably not more than 0.015% by weight;chromium [Cr] between 15% by weight and 30% by weight, preferably between 16.5% by weight and 18.5% by weight or between 17% by weight and 19% by weight;molybdenum [Mo] between 2% by weight and 3% by weight, preferably not more than 2.5% by weight;nickel [Ni] between 5 wt % and 20 wt %, preferably between 10 wt % and 13 wt % or 12.5 wt % and 15 wt %; andnitrogen [N] between 0 wt.% and 0.1 wt.%.Particularly preferably, the first layer is formed from the AISI 316L steel or the stainless steel EN 1.4404.The second layer is applied (directly adjacent in a two-layer system) to the first layer and is also referred to as a friction layer in the case of a use with frictional loading. In contrast to the first layer, the second layer comprises a technically relevant amount, preferably an amount of hard material particles determining the mechanical properties. It is formed from a so-called MMC material ([Metal Matrix Composite]). For example, an amount is from 20% to 70% by volume in the matrix alloy.Preferably, an amount of hard material particles of at least 35% by volume to 70% by volume or 20% by volume to 60% by volume, particularly preferably of 40% by volume to 50% by volume, is added separately. In a preferred embodiment, the separately added hard material particles are greater than 1 μm [one micrometer], particularly preferably greater than 1.5 μm [fifteen tenths of micrometers].The iron-based alloy of the matrix material is in one embodiment identical or identical to the above.In one embodiment, the matrix material of the second layer is formed from the AISI 430L steel or the stainless steel EN 1.4016.In an advantageous embodiment (with iron [Fe] as the remainder (with unavoidable impurities) the following chemical components are included:preferably from 0.5% to 15.0% by weight of vanadium; andpreferably at most 4.0% by weight niobium; andpreferably further at most 0.35% by weight titanium; andpreferably further at most 0.3 wt % nickel; andfurther preferably from 0.3 wt % to 3.0 wt % carbon; andfurther preferably from 10% by weight to 26% by weight chromium; andmore preferably from 1.0% to 10% by weight of manganese; andfurther preferably from 0.05 wt % to 1.0 wt % molybdenum; andfurther preferably from 0.25 wt % to 1.25 wt % silicon; andfurther preferably at most 0.75% by weight tungsten; andfurther preferably at most 0.15% by weight phosphorus; andfurther preferably at most 0.25 wt % sulfur; andfurther preferably from 0.01 wt % to 0.5 wt % nitrogen; andfurther preferably 0.01 wt % to 0.09 wt % oxygen.The present inventors have surprisingly found that the coating system proposed herein can be produced with vanadium. Vanadium [V] represents a relatively inexpensive constituent in comparison with tungsten [W], niobium [Nb] and / or titanium [Ti].Vanadium, titanium and / or niobium serve primarily as so-called carbide formers in the coating system.With the use of vanadium, more expensive components such as niobium and titanium can be used in significantly smaller amounts. Preferably, the welding material does not comprise niobium and titanium, at least not beyond usual impurities.It has surprisingly been found that the profile of properties of corresponding alloys can be matched to the precise aim by the coordinated addition of monocarbide formers such as vanadium. By a fine distribution (finely dispersed precipitation of primary vanadium carbide), in conjunction with grain refining effects, the crack length of the welding layers, which are often subject to severe cracking, can be shortened. A striking wear stress thus no longer leads to immediate break-outs. This results in advantages in abrasive and beating wear stresses. A further advantage lies in the enormous high hardness and the high melting point of vanadium carbide, which ranges in the range of titanium carbide and above tungsten carbide. Vanadium carbide has a hardness of 2950 HV 0.01 [two thousand nine hundred fifty hardness Vickers], 0.102 kp [one hundred two thousandths of kilopond] test force and a standard load time of 10 s [ten seconds] to 15 s, and a melting point at 2830° C. [two thousand eight hundred thirty degrees Celsius].The resulting mixed carbides of type (Cr, Fe) 7C3have a hardness of 1700 HV 10 [one thousand seven hundred hardness Vickers] to 2100 HV 10. From a content of about 0.6% by weight, boron leads to hardening of the (Cr, Fe) 7C3 carbides. The most important hard materials besides Cr7C3 are the chromium carbides Cr3C2 and Cr23C6. Under abrasion wear, the Cr7C3carbides and Cr23C6carbides, which have a needle-shaped to plate-shaped structure, have proven particularly successful.In addition, the addition of manganese [Mn] and silicon [Si] (in addition to a typically marked improvement in the welding properties as a result of the high oxygen affinity and thus deoxidization) leads to an increase in the wear resistance of the applied coating system.By a higher proportion of vanadium, in particular an increased hardness of the coating system can be achieved. However, too high a content of vanadium may result in the lattice being stressed too strongly.It should be noted that the comparisons listed herein are made to a composition having less or more of the respective element in the coating system. It is at least correct that a less or more of this element is present by a corresponding more or less of the iron [Fe] as the base. Alternatively or additionally, a greater or lesser amount of another of said elements is present in an amount considerable within said ranges. In some examples, explicit reference is made to this, provided that the respective element can be used as a substitute. However, it is also within the specialist ability, at least on the basis of the explanations given herein, to use a suitable alloy within the scope of the invention proposed here, in which the elements are present in a combination which are not given here as explicit example.The more vanadium used, the more additional carbide formers can be dispensed with, such as niobium and titanium, but also molybdenum. It should be noted that here it is not necessary to replace the other carbides in the same amount because vanadium carbide occurs very finely divided and, due to its high hardness and high melting point, is among the very high-quality carbides.Preferably, such a coating system comprises at least 0.75 wt %, more preferably at least 1.0 wt %, more preferably at least 1.6 wt %, more preferably at least 2.5 wt %, and more preferably at least 5.0 wt % vanadium.Similarly, a relatively low proportion of vanadium is advantageous because the tendency to crack can be reduced as a result. However, too low a content of vanadium may be disadvantageous because a sufficiently high hardness may not be achieved.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system comprises at most 15% by weight, preferably at most 12.5% by weight, further preferably at most 12% by weight and further preferably at most 10% by weight of vanadium.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system comprises: preferably from 0.5% by weight to 15.0% by weight, further preferably from 0.75% by weight to 15.0% by weight, further preferably from 1.0% by weight to 15.0% by weight, further preferably from 1.6% by weight to 15.0% by weight, further preferably from 2.5% by weight to 15.0% by weight, further preferably from 5.0% by weight to 15.0% by weight, further preferably from 0.5% by weight to 12.5% by weight, further preferably from 0.75% by weight to 12.5% by weight, further preferably from 1.0% by weight to 12.5% by weight, further preferably from 1.0% by weight to 12.5% by weight, further preferably from 1.6% by weight to 12.5% by weight, further preferably from 2.5% by weight to 12.5% by weight, further preferably from 5.0% by weight to 12.5% by weight, further preferably from 0.5% by weight to 12.0% by weight, further preferably from 0.75% by weight to 12.0% by weight, further preferably from 1.0% by weight to 12.0% by weight, further preferably from 1.6% by weight to 12.0% by weight, further preferably from 2.5% by weight to 12.0% by weight and further preferably from 5.0% by weight to 12.0% by weight, preferably from 0.5% by weight to 10.0% by weight, further preferably from 0.75% by weight to 10.0% by weight, further preferably from 1.0% by weight to 10.0% by weight, further preferably from 1.6% by weight to 10.0% by weight, further preferably from 2.5% by weight to 10.0% by weight and further preferably from 5.0% by weight to 10.0% by weight of vanadium.In an advantageous embodiment, the coating system comprises a proportion of niobium. A proportion of niobium is present in the coating system as carbide former.Likewise, a relatively low proportion of niobium is advantageous in order to keep the costs of the coating system low.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further comprises at most 4.0% by weight niobium.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system comprises: preferably at most 3.5 wt %, further preferably at most 3.0 wt %, further preferably at most 2.0 wt %, further preferably at most 1.0 wt %, further preferably at most 0.75 wt %, further preferably at most 0.5 wt %, further preferably at most 0.25 wt %, further preferably at most 0.1 wt % and further preferably at most 0.01 wt % niobium.In an advantageous embodiment, the coating system comprises a proportion of titanium.A proportion of titanium is present in the coating system as carbide former and / or corrosion protection element. Likewise, a relatively low proportion of titanium is advantageous in order to keep the costs of the coating system low.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further comprises at most 0.4 wt % titanium.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system comprises: preferably further at most 0.35% by weight, further preferably at most 0.25% by weight, further preferably at most 0.1% by weight and further preferably at most 0.01% by weight titanium.In an advantageous embodiment, the coating system comprises a proportion of nickel.Nickel [Ni] in the coating system serves in particular for increased corrosion protection. The weldability is also improved by a higher proportion of nickel. Similarly, a relatively low proportion of nickel is advantageous in order to be able to reduce the proportion of health-related substances to a minimum, or also in order to meet more modern standards, such as the so-called reach regulation.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further comprises at most 0.5 wt % nickel, preferably further at most 0.3 wt %, further at most 0.2 wt %, further preferably at most 0.1 wt % and further preferably at most 0.01 wt % nickel.In an advantageous embodiment, the coating system comprises a proportion of carbon [C].Carbon in the coating system serves in particular as a so-called carbide former. A higher proportion of carbon may be detrimental to weldability. At the same time, the hardness can be advantageously increased by a higher proportion of carbon. Likewise, a relatively low proportion of carbon is advantageous in order to improve weldability. Likewise, a relatively low proportion of carbon advantageously lowers the crack formation.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system preferably further comprises at least 0.3 wt % carbon.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system preferably further comprises at least 0.5 wt %, further preferably at least 0.75 wt %, further preferably at least 1.0 wt % and further preferably at least 1.5 wt % carbon.Such a high proportion of carbon is advantageous for austenite formation. It should be noted that a high proportion of the carbon in the powder material reacts during build-up welding and does not matter in the alloy of the coating system, for example with penetrated atmospheric oxygen.For example, in the alloy of the coating system with the aforementioned amount, a proportion of carbon of 0.5 wt % to 1.5 wt % is achieved in the welding material.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 4.5 wt %, further preferably at most 3.0 wt %, further preferably at most 2.5 wt % and further preferably at most 2.0 wt % carbon.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system comprises: further preferably from 0.3% by weight to 5% by weight, further preferably from 0.5% by weight to 5% by weight, further preferably from 0.75% by weight to 5% by weight, further preferably from 1.0% by weight to 5% by weight, further preferably from 1.5% by weight to 5% by weight, further preferably from 0.3% by weight to 4.5% by weight, further preferably from 0.5% by weight to 4.5% by weight, further preferably from 0.5% by weight to 4.5% by weight, further preferably from 0.75% by weight to 4.5% by weight, further preferably from 1.0% by weight to 4.5% by weight, further preferably from 1.5% by weight to 4.5% by weight, further preferably from 0.3% by weight to 3.0% by weight, further preferably from 0.5% by weight to 3.0% by weight, further preferably from 0.75% by weight to 3.0% by weight, further preferably from 1.0% by weight to 3.0% by weight, further preferably from 1.5% by weight to 3.0% by weight, further preferably from 0.3% by weight to 2.5% by weight, further preferably from 0.5% by weight to 2.5% by weight, further preferably from 0.5% by weight to 2.5% by weight, further preferably from 0.75% by weight to 2.5% by weight, further preferably from 1.0% by weight to 2.5% by weight, further preferably from 1.5% by weight to 2.5% by weight, further preferably from 0.3% by weight to 2.0% by weight, further preferably from 0.5% by weight to 2.0% by weight, further preferably from 0.75% by weight to 2.0% by weight, further preferably from 1.0% by weight to 2.0% by weight and further preferably from 1.5% by weight to 2.0% by weight of carbon.In an advantageous embodiment, the coating system comprises a fraction of chromium.Chromium is an important constituent for corrosion resistance to above all aqueous solutions, for example (salt-added) rainwater. In conjunction with molybdenum, it is particularly effective against pitting corrosion. The lower the proportion, the less expensive the welding material. Too small a proportion of chromium, however, may seriously deteriorate corrosion resistance. Chromium in the coating system effectively prevents iron oxide formation, especially when exposed to (low) oxygen, especially when processed under a protective gas atmosphere. A fraction of chromium advantageously serves in the coating system for increased corrosion protection and as carbide former. In addition, however, chromium in the proposed welding material represents a component for hard phase formation.A higher proportion of chromium in particular increases the corrosion resistance of the coating system.In a further preferred embodiment of the base body with the coating system, the chromium is present freely in the matrix. This is particularly advantageous in order to be able to ensure corrosion protection. Bonded chromium in the form of chromium carbides may not contribute to corrosion protection. The skilled person will recognize that vanadium in the coating system proposed here is thus used simultaneously as a victim (sufficiently high) so that carbon is advantageously bonded to vanadium and not to chromium.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 10 wt %, further preferably at least 12.5 wt %, further preferably at least 13 wt % and further preferably at least 15.0 wt % chromium.A proportion of at least 12.0% by weight chromium in the coating system is particularly preferred.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 25 wt %, further preferably at most 20 wt % chromium.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises from 10% by weight to 25% by weight, further preferably from 12.5% by weight to 25% by weight, further preferably from 13% by weight to 25% by weight, further preferably from 15.0% by weight to 25% by weight, further preferably from 10% by weight to 20% by weight, further preferably from 12.5% by weight to 20% by weight, further preferably from 13% by weight to 20% by weight, further preferably from 15.0% by weight to 20% by weight, chromium.In an advantageous embodiment, the coating system comprises a proportion of manganese.Manganese [Mn] in the coating system serves in particular to improve weldability, strength and wear resistance, and also to optimize hardenability. A pronounced equilibrium of manganese is advantageous in order to avoid higher fractions of brittle phases. The carbon together with the manganese assists the formation of austenite (cubic surface-centered lattice structure of an iron alloy) and thus a desired toughness of the coating system. The proportion of manganese is also an effective work hardening agent.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 1.0% by weight, further preferably at least 1.25% by weight and further preferably at least 1.4% by weight of manganese.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 10 wt %, further preferably at most 7.5 wt % and further preferably at most 6.5 wt % manganese.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises from 1.0% by weight to 10% by weight, further preferably from 1.25% by weight to 10% by weight, further preferably from 1.4% by weight to 10% by weight, further preferably from 1.0% by weight to 7.5% by weight, further preferably from 1.25% by weight to 6.5% by weight, further preferably from 1.4% by weight to 6.5% by weight and further preferably from 1.4% by weight to 6.5% by weight, manganese.In an advantageous embodiment, the coating system comprises a proportion of molybdenum.Molybdenum [Mo] in the coating system serves in particular advantageously for improving weldability and fine grain formation. In addition to the above-described properties, molybdenum has the property of providing corrosion resistance to nonoxidizing solutions, such as hydrochloric acid, which also occur in the environment in amounts which are not negligible. Molybdenum is also a further carbide former. A higher proportion of molybdenum accordingly increases the corrosion resistance in particular.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 0.05 wt %, further preferably at least 0.1 wt % and further preferably at least 0.25 wt % of palladium oxide.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 1.0% by weight, further preferably at most 0.75% by weight and further preferably at most 0.6% by weight of molybdenum.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises from 0.05 wt. % to 1.0 wt. %, further preferably from 0.1 wt. % to 1.0 wt. %, further preferably from 0.25 wt. % to 1.0 wt. %, further preferably from 0.05 wt. % to 0.75 wt. %, further preferably from 0.1 wt. % to 0.75 wt. %, further preferably from 0.25 wt. % to 0.75 wt. %, further preferably from 0.05 wt. % to 0.6 wt. %, further preferably from 0.1 wt. % to 0.6 wt. % and further preferably from 0.25 wt. % to 0.6 wt. % molybdenum.In an advantageous embodiment, the coating system comprises a proportion of silicon.A higher proportion of silicon [Si] advantageously increases, in particular, the wear resistance and the strength of the coating system.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 0.1% by weight of silicon.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 0.25 wt %, further preferably at least 0.3 wt %, and further preferably at least 0.5 wt % silicon.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 1.25 wt %, further preferably at most 1.0 wt % and further preferably at most 0.7 wt % silicon.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises from 0.25% by weight to 1.25% by weight, further preferably from 0.3% by weight to 1.25% by weight, further preferably from 0.5% by weight to 1.25% by weight, further preferably from 0.25% by weight to 1.0% by weight, further preferably from 0.3% by weight to 1.0% by weight, further preferably from 0.5% by weight to 1.0% by weight, further preferably from 0.25% by weight to 0.7% by weight, further preferably from 0.3% by weight to 0.7% by weight, and further preferably from 0.5% by weight to 0.7% by weight of silicon.In an advantageous embodiment, the coating system comprises a proportion of tungsten.Tungsten [W] is advantageous in very small amounts as carbide former (for example for a high-friction-resistant and / or high-heat-resistant surface). However, it is particularly advantageous in even small amounts as a solid solution solidifier and for the high-temperature resistance of the coating system.Tungsten carbides have proven to be an effective hard material addition in the prior art, in particular in so-called dual-layer systems. They significantly increase the hardness of a welded-on layer. A disadvantage is that they make the welding process more difficult because it is necessary to ensure a uniform distribution of the carbides in the melt. In addition, melting of the carbides should be prevented in order to take advantage of the technological advantage of the carbides and to reduce the risk of embrittlement of the matrix. Moreover, their high price is a problem for economy. A higher proportion of tungsten advantageously increases the hot strength of the coating system in particular. Tungsten also advantageously serves as a carbide former. However, a high proportion of tungsten may be uneconomical due to high material costs.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 0.75 wt %, further preferably at most 0.6 wt %, further preferably at most 0.5 wt %, further preferably at most 0.25 wt %, further preferably at most 0.05 wt %, and further preferably at most 0.01 wt % tungsten.In an advantageous embodiment, the coating system comprises a proportion of phosphorus.A relatively low proportion of phosphorus [P] is advantageous here, because phosphorus is disadvantageous as a steel pest.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 0.15 wt %, further preferably at most 0.1 wt %, further preferably at most 0.05 wt %, and further preferably at most 0.25 wt % phosphorus.The coating system comprises a portion of sulfur in one embodiment.A relatively low proportion of sulfur [S] is advantageous in this case. The skilled person will recognize that sulfur is bound by manganese.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 0.25 wt %, further preferably at most 0.1 wt % and further preferably at most 0.01 wt %, sulfur.The coating system comprises a proportion of nitrogen in one embodiment.In the prior art, nitrogen-alloyed steels are increasingly being used. However, the skilled worker will generally consider nitrogen as a steel pest and keep the proportion of nitrogen [N] as low as possible. Nitrogen may be used as the alloying component.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at most 0.5 wt %, further preferably at most 0.25 wt %, and further preferably at most 0.1 wt % nitrogen.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises at least 0.01 wt %, further preferably at least 0.02 wt % and further preferably at least 0.05 wt % nitrogen.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises from 0.01 wt % to 0.5 wt %, further preferably from 0.02 wt % to 0.5 wt %, further preferably from 0.05 wt % to 0.5 wt %, further preferably from 0.01 wt % to 0.25 wt %, further preferably from 0.02 wt % to 0.25 wt %, further preferably from 0.05 wt % to 0.25 wt %, further preferably from 0.05 wt % to 0.25 wt %, further preferably from 0.01 wt % to 0.1 wt %, further preferably from 0.02 wt % to 0.1 wt %, further preferably from 0.05 wt % to 0.1 wt %, further preferably from 0.05 wt % to 0.1 wt % nitrogen.The coating system comprises a proportion of oxygen in one embodiment.A relatively low proportion of (elemental) oxygen [O] is advantageous here, because this can lead to embrittlement and further negative properties. It is noteworthy that some of the further described alloying constituents may also have a deoxidizing effect. Those skilled in the art will appreciate that oxygen should be advantageously avoided and other alloying constituents may also be designed to counteract oxygen impurities.In a further preferred embodiment of the base body with the coating system, the matrix alloy of the coating system further preferably comprises 0.01 wt % to 0.09 wt % oxygen.The first grain group comprises hard material particles, such as borides and / or carbides. In one embodiment, carbides are used, for example, tungsten carbide [WC], titanium carbide [TiC], vanadium carbide [VC] and / or chromium carbide [for example, Cr3C2]. The hard material particles of this first grain group comprise a grain size of 2 μm [two micrometers] to 60 μm, preferably 10 μm to 50 μm, particularly preferably 15 μm to 45 μm. It should be noted that these grain sizes within the first grain group according to a Gaussian distribution are at least 80% [eighty percent], preferably more than 90%, of the hard material particles. The hard material particles of the first grain group are preferably prepared as powders in the application process, wherein the hard material particles are preferably not melted, preferably not melted, i.e. are applied in the core or completely unchanged and are embedded in the matrix alloy.By using a relatively small grain size, it is ensured with high probability that even with a high proportion of hard material particles of, for example, up to 70% by volume between the hard material particles, a sufficient volume of material of the matrix alloy is present, despite the stochastically arbitrary distribution of the hard material particles in the matrix alloy, so that here a weak point is not caused in the matrix alloy by two hard material particles arranged closely together. Furthermore, as the size of the hard material particles increases, the notch twist is increased.It is proposed here that residual compressive stress is present in the first layer. This is accomplished, for example, by means of the introduction of forming work after build-up welding. Alternatively or additionally, an application method generating intrinsic compressive residual stresses is used, such as LTT [Low Transformation Temperature] and PVD [Physical Vapor Deposition] (especially sputtering or ion plating). Because relatively large layer thicknesses are desired for many applications or it has proven advantageous to provide the first layer with a large layer thickness, build-up welding, in particular high-speed laser build-up welding, is suitable, wherein intrinsic residual stresses (as a result of the so-called welding contraction) are generated at least in the applied material.By means of the introduction of forming work, residual compressive stresses in the relevant layer are converted into residual compressive stresses (and, if appropriate, at least reduced or neutralized in a boundary region of the base body beneath it). It has been assumed up to now that introducing forming work of an intermediate layer will not bring any advantage because the subsequent application of the further layer is canceled again on account of the thermal input and the mixing zone of so-called welding contraction. At least, however, it was believed that a final introduction of forming work (on the last layer) would lead to the hoped advantages.However, it has been shown to the contrary that the introduction of forming work does not act in the lower layers. It should be noted that in an embodiment with a (first) layer embodied in multiple layers and a small thickness of the individual layers, a plurality of layers are jointly subjected to a forming work, for example up to a thickness of more than 50 μm [fifty micrometers], preferably of more than 80 μm, preferably up to 500 μm.It should be noted that the introduction of forming work in one embodiment is carried out multiple times, for example after each application of a layer, or exclusively once, for example after application of the layer or all of its layers.In a preferred embodiment, a residual compressive stress is present solely in the first layer and, in the second layer, for example, the intrinsic residual compressive stresses (introduced, for example, as a result of the build-up welding) are present. It should be noted that the residual compressive stresses in the second layer are reduced, for example, as a result of the residual compressive stresses in the first layer compared to an embodiment with neutral residual compressive stress or at least compared to an embodiment with residual compressive stresses in the first layer.It is furthermore proposed in an advantageous embodiment of the workpiece that the residual compressive stress is generated in the first layer by means of mechanical compacting, wherein the second layer has preferably been applied only after the compacting of the first layer.A suitable manufacturing method is the introduction of forming work by means of at least one of the following methods:rolling;- pressing;peening; and- pressing,wherein preferably the base body coated with (at least) the first layer is cooled beforehand.In one embodiment, the relevant layer comprises a plurality of plies or is applied in a plurality of plies. In a preferred embodiment, forming work is applied to each or a plurality of these layers before the next layer is applied. Preferably, the last layer and / or the (entire) uppermost layer remains uncompacted.Preferably, the forming work of the respective layer is carried out at room temperature up to a maximum of 400° C. [four hundred degrees Celsius], so that a desired structure is formed in the material of the respective layer.In a preferred embodiment, the mechanical compaction of the first layer is carried out before the second layer is applied, wherein preferably no forming work is (or is) introduced into the second layer and particularly preferably is applied directly adjacent to the first layer. An advantage of not post-compacting the second layer is that the structure is undisturbed and, in particular, the embedded hard material particles (often brittle) are not damaged, for example broken up and / or released from the enclosure in the matrix material.It is furthermore proposed in an advantageous embodiment of the workpiece that the second layer comprises a second grain group of agglomerated hard material particles.On the one hand, it has surprisingly been found that the avoidance of fine dust emission and the crack resistance cause mutually opposite requirements for the proportion of hard material particles in the second layer. Namely, for low fine dust emission, it is necessary to provide a high proportion of hard material particles in the second layer. On the contrary, for good crack resistance, it is necessary to provide a small proportion of hard material particles in the second layer. An optimum must therefore be set here. Such an optimum is less than 35% by weight, preferably less than 25% by weight, particularly preferably less than 20% by weight. In one embodiment, together with the first grain group, a total volume fraction of the hard material particles on the second layer (i.e. the MMC material), as already mentioned above, is between 30 vol. % and 70 vol. %, preferably at 40 vol. % and 60 vol. %, particularly preferably about 50 vol. %.Moreover, however, it has been found on this side that it is advantageous to use relatively small hard material particles, as already mentioned above (first grain group), preferably of less than 10 μm [ten micrometers], wherein these are combined to form mixed particles of preferably 15 μm to 53 μm or 45 μm to 90 μm. As said, the embedding of the hard material particles is thus improved.When the agglomerated hard material particles are introduced by means of a thermal application method (for example build-up welding), the so-called binder (or at least a part thereof), for example formed from an iron-chromium alloy [FeCr], is melted, such that the very small hard material particles are then distributed in the melt and (as in the case of the hard material particles of the first grain group) are wetted by the melt and fixed during solidification of the matrix alloy.It is furthermore proposed in an advantageous embodiment of the workpiece that the first layer comprises a nickel content of at most 15% by weight, preferably of at least 10% by weight.A high nickel content in the first layer provides good corrosion resistance and ductility, so that there is a low tendency to crack and introduced stresses (for example during the braking process in the case of a brake disc) cannot (so easily) penetrate into the base body and / or lead to detachment of the coating system.It should be noted that the first layer does not lie on the surface during operation and also does not reach the surface over a service life and thus does not become part of abrasion (fine dust). Thus, under any consideration, it is reliably and entirely foreseeable that it will be legally permissible to use a relatively high proportion of nickel in the first layer. In the case of a brake disk, at the latest with the loss of the second layer (friction layer), operation of the brake disk is no longer reliable with regard to its braking properties and therefore has to be replaced. A nickel-loaded fine dust emission is therefore virtually ruled out.It is furthermore proposed in an advantageous embodiment of the workpiece that the matrix alloy of the second layer comprises a nickel content of at most 0.5 wt %, preferably of at most 0.3 wt %, particularly preferably of at most 0.01 wt %.In many applications, the second layer is directly exposed to the environment and the environmental influences and, if appropriate, to a chemical (for example corrosion) and / or mechanical load (for example, friction in the case of a brake disk as a friction layer). As described above, it is considered to be advantageous that the nickel content in a fine dust emission is negligibly small. It is therefore proposed here that the nickel content in the matrix alloy is very low up to an unavoidable impurity, i.e. not appreciable.It is furthermore proposed in an advantageous embodiment of the workpiece that the first layer has an application thickness of more than 50 μm, preferably of more than 80 μm, preferably up to 500 μm.Because crack formation always begins from the outside and is to continue as far as possible not into the base body or into the attachment plane between the coating system and the base body, it is proposed here to provide a (first) application thickness that is as large as possible. Because overall the smallest possible application thickness, a minimum (first) application thickness of the first layer is a minimum of 50 μm [fifty micrometers], preferably more than 160 μm, preferably up to 500 μm.It is furthermore proposed in an advantageous embodiment of the workpiece that the second layer has an application thickness of less than 300 μm, preferably less than 150 μm, particularly preferably less than 100 μm.Because crack formation always begins from the outside and it has been found that this cannot be stopped completely efficiently in the MMC material, it is proposed here to provide the smallest possible (second) application thickness. However, since the second layer as outer layer (for example friction layer) is directly exposed to the environment and the environmental influences, the minimum is preferably 50 μm [fifty micrometers], preferably 80 μm, particularly preferably 90 μm, for a long service life.The values mentioned are particularly advantageous for a brake disc for passenger cars, above all in terms of costs. For trucks, for example, a greater (second) application thickness of the second layer is significantly greater due to higher loads and / or a longer operating time, for example up to 300 μm [three hundred micrometers].It should be noted that the (second) application thickness is defined according to its final dimensions after a possible subsequent compacting and / or flat grinding. Alternatively, the second layer is not post-treated and the (second) application thickness corresponds to the application thickness. In one embodiment, this also applies to the (first) application thickness of the first layer, wherein this is preferably not post-treated by grinding.In one embodiment, a surface roughness of the outer surface formed by the second layer is brought to an averaged roughness depth R z of less than 5 μm [five micrometers], particularly preferably between 2 μm and 4 μm or 2 μm to (technically) 0 μm, for low particulate emission and at the same time good surface property. The averaged roughness depth R z is given in the standard DIN EN ISO 4287:1984. The averaged roughness depth R z is determined as follows:A defined measurement path on the surface of the workpiece is divided into seven individual measurement paths, wherein the middle five measurement paths are of the same size. The evaluation takes place only over these five measurement paths, since the Gaussian filter to be used requires half an individual measurement path leading or trailing or a convolution has a non-negligible inflow behavior and outflow behavior. The difference between the maximum and minimum values is determined from each of these individual measurement paths of the profile. From the five individual roughness depths thus obtained, the mean value is formed as the averaged roughness depth Rz. It should be noted that this characteristic value is not to be confused with the roughness depths Rt and R max, respectively. R t is defined as the difference between the maximum and minimum value of the profile (R p-R v) with respect to the total measurement distance, that is to say the five individual measurement distances in the normal case. R max is the largest of the five individual roughness depths of the above-mentioned measuring methods.It is furthermore proposed in an advantageous embodiment of the workpiece that the hard material particles of at least the first grain group are formed in broken form and / or the hard material particles comprise carbides, preferably titanium carbides.At present, usually so-called spheroidized hard material particles are used. Such hard material particles are complicatedly post-processed, the aim being that they trigger a low notch effect when incorporated into a matrix alloy. It is proposed here that this complicated (and thus cost-driving) step is dispensed with. It has been found on this side that this is possible when a small grain size (as proposed herein for the first grain group) is used. The notch effect is then already sufficiently reduced due to the smaller grain size (the first grain group). A cost advantage for the second grain group can likewise be achieved with broken hard material particles.In one embodiment, hard material particles are borides, i.e. (usually binary) compounds formed with boron [B], usually with a metal, borides forming ceramic properties. Hard material particles (particularly preferably exclusively) in this application are preferably carbides, as (usually binary) compounds formed with carbon [C], usually with a metal, wherein carbides form ceramic properties. Titanium carbides [TiC] are particularly preferably used, whereby cost advantages over tungsten carbides [WC] and advantages with regard to hardness are achieved over vanadium carbides [VC]. In addition, titanium carbides have the advantage of a very high melting point, so that high temperatures or energy inputs are possible during build-up welding compared to tungsten carbides, chromium carbides and silicon carbides, for example.It is furthermore proposed in an advantageous embodiment of the base body that the two layers are applied to the base body by means of build-up welding, preferably high-speed laser build-up welding.High-speed laser deposition welding allows extremely fast and also reliable deposition of low deposition thicknesses compared to other deposition welding methods, for example with an area rate of at least 500 cm 2 / min [five hundred square centimeters per minute] to a reference layer thickness of 100 μm [one hundred micrometers]. In addition, melting zones and mixing zones can be set very small because the heat input is introduced very specifically (focused laser beam) and briefly (rapid advance), and (at least most of the material of) the welding filler material is already melted or (sufficiently) melted before it impinges on the surface to be coated.It is furthermore proposed in an advantageous embodiment of the workpiece that the workpiece is a rotary workpiece having an axis of rotation, preferably a brake disc for a motor vehicle.The workpiece proposed here is the end product or a semi-finished product for an end product, as can be used industrially, wherein the base body is provided with a coating system as described above and is preferably applied by means of a method as described above. In one embodiment, the workpiece comprises exclusively the base body and the coating system. Alternatively or additionally, the workpiece is composed of a plurality of individual parts, for example of a plurality of such basic bodies with coating system or other components.It is proposed here that the workpiece is a rotary workpiece, wherein the rotary workpiece is preferably rotated about its central axis of rotation when the coating system is applied. Often, a single feed axis for the coating unit is then sufficient for applying the coating system. In the case of a cylindrical shape of the treatment surface, this feed axis is oriented parallel to the axis of rotation (corresponding to the cylinder axis). In the case of a cylinder cover shape or disk shape of the treatment surface, this feed axis is oriented parallel to the radius to the axis of rotation (corresponds to the cylinder axis or disk axis). Preferably, a feed axis or adjustment axis is also provided, wherein it is particularly preferably movable in the coating process or during the measuring process, adapted to the coating speed or to the measuring speed. Alternatively, the feed axis is movable only more slowly and it is set only before the beginning of application of the coating system or metering or an intermediate step of the relevant process.In an advantageous embodiment, the rotary workpiece is a brake disc for a motor vehicle (including a commercial vehicle). The outer surface formed by the second layer is the friction surface which comes into contact with a brake pad during operation when the motor vehicle is accelerating.According to a further aspect, a method for coating a base body of a workpiece according to an embodiment according to the above description is proposed, wherein at least one, preferably all, of the layers are applied by means of build-up welding, preferably laser build-up welding, particularly preferably high-speed laser build-up welding, preferably with an area rate of at least 500 cm 2 / min to a reference layer thickness of 100 μm, wherein preferably the residual compressive stress is generated in the first layer applied to the base body by means of mechanical compaction, and subsequently the second layer is applied to the compacted first layer.Here, an advantageous method for forming the coating system on a base body as described above is proposed. Reference is made to the preceding description at least with regard to possible embodiments of the method and to the preceding description of the base body and its coating with regard to the product of the method.The invention described above is explained in detail below in view of the relevant technical background with reference to the associated drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, it being noted that the drawings are not dimensionally accurate and are not suitable for defining size ratios. It is shown in FIG. 1 : a micrograph of a workpiece with coating system with a crack as far as the treatment surface; FIG. 2 : a micrograph of a workpiece with coating system with a crack to just before the treatment surface; FIG. 3 : a micrograph of a workpiece with a coating system with hard material particles of small grain size; FIG. 4 : a micrograph of a workpiece with a coating system with hard material particles of small and very small grain size; FIG. 5 is a schematic sectional view through a workpiece with a multi-layer coating with a superficial crack; FIG. 6 : a graph with a periodic load over time; and FIG. 7 : shows a motor vehicle with brake disks in a schematic plan view.FIG. 1 shows a micrograph of a workpiece 1 with coating system 2 having a crack 22 as far as the treatment surface 23. At the bottom of the illustration, the base body 3 can be seen in section as a lamellar gray casting body, which directly adjoins the first layer 4 (also referred to as adhesive layer) with its treatment surface 23, to which the coating system 2 has thus been applied. The difference can be clearly seen at least in that no lamellae are formed in the coating system 2. The first layer 4 is characterized in that no hard material particles 8 are contained here. Here, only voids and cracks 22, as well as grinding tracks from the creation of the grinding for the shown micrograph are to be seen, and this first layer 4 acts homogeneously with the shown resolution. The first layer 4 shown here is formed by an iron-based alloy 6, namely the steel AISI 316L containing a significant nickel fraction.In the first layer 4 there is residual compressive stress 9, here by means of the introduction of forming work (compare FIG. 5 ). The first layer 4 and the second layer 5 are formed by high-speed laser deposition welding at an area rate of at least 500 cm 2 / min to a reference layer thickness of 100 μm.Immediately adjoining the first layer 4 in this embodiment shown is the second layer 5 (for example in the case of a brake disc 15, compare FIG. 7, referred to as friction layer), which is characterized in particular in that (large) hard material particles 8 can be seen there, of which three pars-pro-toto are provided with reference numerals here. In the present example, these are brittle (i.e. non-spheroidal) titanium carbides. According to the top illustration, the outer surface 27 of the second layer 5 (in the case of a brake disc 15 configured for frictional contact with a brake pad 25) adjoins the environment, that is to say air. A (purely optional) special feature here is that the outer surface 27 is plane-ground and is therefore embodied to be very planar. It has been found that such a low surface roughness R z[average roughness depth] of, for example, approximately 5 μm, preferably less, for example 3 μm, particularly preferably 2 μm to (technically) 0 μm is favourable for a low fine dust emission and at the same time not detrimental for a good braking action when used in a brake disc 15.The matrix alloy 7 of the second layer 5 shown here is likewise formed by an iron-based alloy 6, namely with an AISI 430L steel containing technically negligible nickel content. In the following table, some possible embodiments of a corresponding iron-based alloy 6 are plotted in their elemental composition. The composition according to elements and in percent by weight: iron (Fe) is present in a balanced (bal) amountIt can be clearly seen here that the (first) application thickness 12 of the first layer 4 is approximately equal to the (second) application thickness 13 of the second layer 5, wherein this is somewhat thicker. These are here approximately a first application thickness 12 of approximately 200 μm and a second application thickness 13 of approximately 240 μm.An undesirably large crack 22 can be seen here, which has passed straight undisturbed from the outer surface 27 into the lower regions of the first layer 4, even through a hard material particle 8. The crack 22 branches out in the first layer 4 and leads to a detached region 28 of the coating system 2 and continues from there into the main body 3. Thus, a free access from the outer surface 27 into the base body 3 is created, which promotes a corrosive under migration of the coating system 2. This can lead to (at least regional) premature detachment of the entire layer structure. At least, however, corrosion-induced (rust formation) fine dust emission is promoted.FIG. 2 shows a micrograph of a workpiece 1 with coating system 2 having a crack 22 right in front of the treatment surface 23. For the details regarding composition and construction, reference is made to the description of FIG. 1 and only the noteworthy differences are discussed here.It can be seen clearly here that the (first) application thickness 12 of the first layer 4 is somewhat thicker than the (second) application thickness 13 of the second layer 5.Here, an improvement in the formation of the crack 22 in comparison with FIG. 1 can be seen; namely, the crack 22 already ends in the first layer 4 and therefore does not penetrate as far as the treatment surface 23 of the base body 3. The base body 3 which is particularly susceptible to corrosion is thus further protected by the remaining barrier of the first layer 4. However, small cracks 22 can be seen in the first layer 4 in the vicinity of the end of the large crack 22, so that there is a risk that, in an unfavorable constellation, penetration up to the treatment surface 23 of the base body 3 can also occur here.FIG. 3 shows a micrograph of a workpiece 1 with coating system 2 with hard material particles 8 of small grain size. For the details regarding composition and construction, reference is made here too to the description of FIG. 1 and only the noteworthy differences are discussed here.It can be clearly seen here that the (first) application thickness 12 of the first layer 4 is significantly thinner than the (second) application thickness 13 of the second layer 5. It should be noted that here the outer surface 27 is not plane ground, but runs clearly undulated. This is advantageous for some applications. Alternatively, approximately 40 μm to 60 μm is ablated to measure or to compensate for tolerances, and / or (alone) preferably until a desired surface roughness is reached.Here, no formation of a crack 22 is observed. The assumption is that this significantly reduces susceptibility to cracks due to the significantly smaller hard material particles 8, introduced here in a (first) grain group 10 having a grain size window of 15 μm to 45 μm.FIG. 4 shows a micrograph of a workpiece 1 with a coating system 2 comprising hard material particles 8 having a first grain group 10 with a small grain size and a second grain group 11 with a very small grain size. For the details regarding composition and construction, reference is made here too to the description relating to FIG. 1 and to FIG. 3 and the noteworthy differences are discussed here alone.Here, two grain groups, namely a first grain group 10 with a grain size window of again 15 μm to 45 μm and a second grain group 11 with agglomerated hard material particles 8 with a grain size of less than 10 μm, are thus accommodated in the matrix alloy 7. In addition, the proportion by volume here is above 50% by volume.Here, too, no formation of a crack 22 is observed. The assumption is that the hard material particles 8 (to be regarded as sparse here) and considerably smaller compared to the embodiments in FIGS. 1 and 2 considerably reduce susceptibility to cracks. The agglomerated hard material particles 8 are introduced for a desired hardness of the second layer 5, which is currently required on the market. At the same time, these agglomerated hard material particles 8 do not entail the disadvantage, owing to their small size, that too little matrix material is present between the individual hard material particles 8. This prevents the brittleness of the hard material particle 8 from determining the susceptibility to cracks.FIG. 5 schematically shows a sectional view through a workpiece 1 with a multi-layer coating with a superficial crack 22. Three materials can be seen by means of different hatchings. The lowermost material in the illustration is that of the base body 3 of the workpiece 1, wherein the coated treatment surface 23 is arranged at the top in the illustration. For example, the material of the workpiece 1 (or of the carrier body) is a lamellar gray casting, wherein the cross-hatched embedded elements are intended to represent the lamellarly deposited carbon. On the treatment surface 23, a first layer 4 (or a plurality of intermediate layers) is formed, by means of which, for example, a first layer 4 is formed with a homogeneous material (purely optionally here), for example as an adhesion layer, preferably without hard material particles 8. The functional layer with embedded hard material particles 8 is shown here.To the right of the sectional view is a graph with the schematic representation of the residual stress 20 in the material with the abscissa (pointing downward), on which the path or the depth 24 in the workpiece 1 is plotted. On the ordinate (horizontal), residual stress 20 in the material is plotted, wherein the residual compressive stress 17 is plotted facing to the right (positive) and the residual compressive stress 9 is plotted facing to the left (negative).The crack 22 is stopped here within the intermediate layer and therefore does not penetrate as far as the treatment surface 23 of the workpiece 1. At least good corrosion resistance is thus achieved. However, detachment of the coating system 2 is also less likely. This result is achieved by forming work having been introduced into the first layer 4. This can be seen in the graph, according to which a residual compressive stress 9 is impressed in the lower (i.e. near the workpiece) region of the intermediate layer and also in the workpiece 1 close to the treatment surface 23. In the second layer 5, on the other hand, a residual tension 17 is impressed (for example as a result of the weld contraction during build-up welding), which tension continues at least into the mixing zone, but under certain circumstances also into the first layer 4.FIG. 6 shows a graph with a periodic tensile stress load (which is idealised purely for illustrative purposes) over time 21, wherein the time 21 is plotted on the abscissa and the residual stress 20 is plotted on the ordinate, the residual stress 17 is plotted positively and the residual compressive stress 9 is plotted negatively. Such a periodic tensile stress load occurs, for example, at a (co-rotating) point of a brake disk 15 in the circumferential direction (as shear stress) when a brake pad 25 is pressed onto the brake disk 15 during a braking operation (compare FIG. 7 ). A workpiece 1 (for example a brake disk 15) with a two-layer coating system 2 (for example according to the illustration in FIGS. 1 to 4 ) with an outer surface 27 of the friction layer used as a friction surface is used here, which outer surface is thus configured for frictional contact with a brake pad 25.The tensile stress load is identical in this schematic illustration exclusively and without exclusion of generality for better understanding in the upper curve 18 (with solid line) and in the lower curve 19 (with dashed line). The difference here is that in the upper curve 18 in the coating system 2 of the brake disc 15 there is already a residual tension 17, for example as shown in FIG. 5 plotted in the graph there, with the difference that there is also a residual tension 17 in the first layer 4. In the case of the lower curve 19, on the other hand, there is a residual compressive stress 9 in the coating system 2 of the brake disc 15, for example as shown in the graph shown in FIG. 5. The tensile load during operation is thus almost completely shifted into the more readily absorbed region of the residual compressive stress 9.FIG. 7 shows a motor vehicle 16 with brake disks 15 in a schematic plan view. The motor vehicle 16 has four wheels 26, wherein in each case two wheels 26 are arranged opposite one another on a common wheel axle (congruent with the axis of rotation 14 of the brake disks 15). In this example, each of the wheels 26 has a brake disk 15 with an axis of rotation 14, wherein the wheel 26 and the brake disk 15 are connected in a torque-proof manner.For example, a coating system 2 as described above is applied to each of the two axially opposite sides of the brake disk 15. Each of the brake disks 15 is associated with a pair of brake pads 25, the brake pads 25 being fixedly connected to the vehicle body. To decelerate the motor vehicle 16, a respective brake pad 25 is pressed (either or individually regulated) against the respective brake disc 15. The braking energy is to a large extent introduced as waste heat into the respective brake disc 15, for which reason the coating system 2 is loaded under high temperatures and high shear load and high pressure. The coating system 2 must withstand this load situation.With the coated workpiece proposed here, crack formation can be sufficiently suppressed.List of reference characters1 Workpiece 2 Coating system 3 Base body 4 Adhesion layer 5 Friction layer 6 Iron-based alloy 7 Matrix alloy 8 Hard material particles 9 Compressive residual stress 10 First grain group 11 Second grain group 12 First application thickness 13 Second application thickness 14 Axis of rotation 15 Brake disc 16 Motor vehicle 17 Tensile residual stress 18 Upper curve 19 Lower curve 20 Residual stress 21 Time 22 Crack 23 Treatment surface 24 Depth 25 Brake pad 26 Wheel 27 Outer surface 28 Detached regionReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2011 100 456 A1

[0008] WO 2021 / 007 209 A1

[0009] WO 2021 / 126 518 A1

[0009] Cited Non-Patent LiteratureSchopphoven et al. ("Experimental and Model Theoretical Studies on Extreme High Speed Laser Deposition Welding", Ph Institute of Laser Technology ILT, 2019, published online on the Internet sites of the University Library

[0008]

Claims

Workpiece (1) with a coating system (2), wherein the coating system (2) is applied to a base body (3) and comprises at least two layers (4, 5), wherein the first layer (4) is applied directly adjacent to the base body (3) and is formed from an iron-based alloy (6), and wherein the second layer (5) is applied to the first layer (4) and is formed as a matrix alloy (7) with an iron-based alloy (6) as a matrix and hard material particles (8) embedded therein, wherein a residual compressive stress (9) is present in the first layer (4), and wherein a first grain group (10) of the hard material particles (8) having a grain size of 2 μm to 60 μm is embedded in the second layer (5).Workpiece (1) according to Claim 1, wherein the residual compressive stress (9) is generated in the first layer (4) by means of mechanical compacting, wherein preferably the second layer (5) has been applied only after the compacting of the first layer (4).The workpiece (1) according to claim 1 or claim 2, wherein the second layer (5) comprises a second grain group (11) of agglomerated hard material particles (8).The workpiece (1) according to any one of the preceding claims, wherein the first layer (4) comprises a nickel content of at most 15 wt.%, preferably of at least 10 wt.%.Workpiece (1) according to one of the preceding claims, wherein the matrix alloy (7) of the second layer (5) comprises a nickel content of at most 0.5 wt.%, preferably of at most 0.3 wt.%, particularly preferably of at most 0.01 wt.%.The workpiece (1) according to any one of the preceding claims, wherein the first layer (4) has an application thickness (12) of more than 50 μm, preferably of more than 80 μm, preferably up to 500 μm.The workpiece (1) according to any one of the preceding claims, wherein the second layer (5) has an application thickness (13) of less than 300 μm, preferably less than 150 μm, particularly preferably less than 100 μm.Workpiece (1) according to one of the preceding claims, wherein the hard material particles (8) of at least the first grain group (10) are formed in broken form, and / or the hard material particles (8) comprise carbides, preferably titanium carbides.The workpiece (1) according to any one of the preceding claims, wherein the workpiece (1) is a rotary workpiece having an axis of rotation (14), preferably a brake disc (15) for a motor vehicle (16).Method for coating a base body (3) of a workpiece (1) according to one of the preceding claims, wherein at least one, preferably all, of the layers (4, 5) are applied by means of build-up welding, preferably laser build-up welding, particularly preferably high-speed laser build-up welding, preferably with an area rate of at least 500 cm 2 / min to a reference layer thickness of 100 μm, wherein preferably the residual compressive stress (9) is generated in the first layer (4) applied to the base body (3) by means of mechanical compaction, and subsequently the second layer (5) is applied to the compacted first layer (4).

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