EP3097300B1 - Piston for a piston machine - Google Patents

Description

The invention relates to a piston for a piston machine, in particular a reciprocating piston engine, according to the preamble of claim 1.

In mechanical engineering, a piston is a moving component that, together with a stationary component, the cylinder, forms a closed combustion chamber, the volume of which can be changed by moving the piston. A simple embodiment of this arrangement is a piston that is immersed in a correspondingly shaped housing. The position of the piston in the housing determines the size of the combustion chamber.

Machines in which pistons are used are called piston machines. The piston machines most widely used today are motor vehicle engines, especially gasoline and diesel engines.

The most common materials used for such pistons are aluminum and steel. In motor vehicle engines, the piston has to transmit the gas forces of the fuel gas to the connecting rod, among other things. In addition, it has the task of sealing the combustion chamber against the crankcase with sealing elements and of transferring the heat transferred to it to the coolant.

To improve performance and efficiency, optimizing engines often leads to increased temperatures and pressures in the combustion chamber and in particular on the piston of an internal combustion engine. For example, diesel engines already work at cylinder temperatures of 650 ° C to around 1100 ° C and effective mean pressures of up to around 2000 kPa. Such conditions in connection with rapid thermal cycling, which are brought about by the combustion process in the cylinder, create a demanding environment for engine parts within the cylinder. To counteract corrosion on the piston crown on the one hand and heat dissipation from the combustion chamber on the other, it makes sense to coat parts of the piston with insulating materials.

One approach to improving the corrosion resistance can be found in in DE 196 03 515 C1 coating on the basis of aluminum and iron described. In addition, the coating contains further alloy elements and impurities, in particular chromium, silicon and carbon.

In DE 10 2006 007 148 A1 discloses a piston which has an iron-aluminum-chromium alloy in order to improve the physical and mechanical properties of the piston, in particular with regard to the strength at higher temperatures.

EP 0 663 020 B1 provides the application of a thermal barrier coating consisting of a metal bond coating, a metal / ceramic layer applied thereon and a ceramic composite material cover layer applied thereon to a piston in order to protect the piston from rapid thermal cycling.

What these approaches have in common is that they reduce the heat dissipation from the cylinder chamber. However, it is disadvantageous that temperature peaks which occur locally on the piston crown during combustion are not diverted, but rather intensify. This leads to a thermal throttling in the gas exchange or an undesired shortening of the ignition delay. On the other hand, there is a strong thermal stress on the material at certain points, with the result that the coating is damaged and the underlying material is destroyed.

The font DE 36 22 301 A1 discloses a piston in which the entire piston crown and also a region of the piston skirt are coated with a heat-insulating layer made of asbestos. It is also proposed to apply a heat-resistant yet thermally conductive layer to the heat-insulating layer on the heat-insulating layer in order to store the heat generated in the combustion chamber in this layer.

The document EP 0 321 159 A2 shows a built piston with a heat-insulating component facing the combustion chamber made of potassium titanate whisker, zirconium dioxide fibers, carbon fibers or aluminum oxide fibers. The component is completely made up of one layer Surrounding silicon nitride or silicon carbide, which is applied by means of vapor deposition.

JP 2012-72747 A describes a piston made of an aluminum alloy, on the piston crown of which a porous layer and a film layer are arranged. The thermal conductivity of the final film layer is greater than that of the underlying porous layer. Composite material composed of a porous metal structure and metallic or inorganic fibers, for example ceramic fibers, is described as the material of the porous layer.

A similar structure is in EP 2 436 896 A1 disclosed, wherein here the porous layer consists of ceramic hollow particles.

The invention is now based on the object of solving or at least reducing the problems of the prior art and further increasing the insulating effect. In particular, a piston is to be provided which achieves a reduction in temperature peaks.

According to the invention, this object is achieved by a piston and a piston machine having the features of the independent claims.

The invention thus relates to a piston for a piston machine, the piston comprising a stack of layers arranged on a piston head of the piston. According to the invention, the stack of layers comprises at least one first layer, which is directly or indirectly connected to the surface of the piston head and comprises a heat-insulating material, and a second layer, which is directly or indirectly connected to the first layer and which contains a thermally conductive material.

The arrangement of a stack of layers according to the invention on the piston crown leads in an advantageous manner to an increase in the efficiency of the combustion process. The efficiency of the internal combustion engine is increased in particular by the fact that less heat is transported away from the combustion chamber or the cylinder chamber. When using a piston according to the invention, higher temperatures prevail in the combustion chamber than known from the prior art. In turn, higher temperatures lead to higher efficiency. In addition, an increase in temperature in the combustion chamber has a positive effect on the exhaust gas treatment, since the exhaust gases also have a higher temperature and thus lead to accelerated heating of the catalytic converters. The stack of layers according to the invention advantageously provides insulation and / or protection against corrosion of the piston surface or the piston on the piston crown.

In contrast to the heat-insulating and thus insulating function of the first layer, the second layer has the function of harmonizing the temperature on the surface of the piston crown. This means that the heat-conducting material of the second layer advantageously ensures temperature equalization on the surface of the layer stack and thus on the surface of the piston crown. This in turn leads to a reduction in locally limited temperature peaks on the substrate surface, since the temperature is evenly distributed over the surface by the heat-conducting second layer. The heat insulating material of the first layer decouples the second layer and thus the heat conduction from the piston crown or from the piston. This ensures that the heat is evenly distributed on the surface of the piston crown of a piston according to the invention without being transported away from the combustion chamber.

A piston according to the invention is used with advantage in piston engines. Piston machines are fluid energy machines in which a displacer defines a periodically changing working space by means of its movement. The displacer is a piston, which can have a cylindrical shape, for example. In the present invention, a piston engine is understood to mean both a rotary piston engine, which has a disc piston, for example, and a reciprocating piston engine, in particular with a cylindrical piston. The area of the piston which faces the combustion chamber and is thus in contact with the fluid is referred to in the present invention as the piston head.

In reciprocating piston engines which have pistons with an essentially cylindrical geometry, this piston head is a top side with a round shape, which is arranged on a cylindrical circumferential side wall, the piston skirt. The piston crown, in turn, can have a wide variety of shapes. In the present invention, both planar and concave or convex shapes of the piston head are possible. The piston head can also have depressions and elevations, for example in the form of lugs, which are let into the piston head and / or protrude from it. The pistons described in the present invention, in particular piston heads, are at least partially manufactured from a light metal alloy or a steel, light metal alloys being preferred as the piston material. Light metal alloys are to be understood in principle as all conceivable light metal alloys. In the present invention however, aluminum alloys are preferred, in particular aluminum-silicon alloys with varying aluminum contents up to hypereutectic concentrations.

A stack of layers is arranged on the surface, in particular on the light metal alloy, of the piston crown of a piston described here. This is to be understood as an arrangement of successively applied layers of different or the same thickness made of different or the same materials, a first layer being arranged directly or indirectly on the piston surface. The layers applied one after the other are basically functional layers, that is to say those which change, in particular improve, at least one physical property of the surface of the piston crown.

The essence of the present invention thus lies in the combination of heat-insulating or heat-conducting properties of the layers. These can be defined via the thermal resistance R _th or its reciprocal value, the thermal conductivity λ. R _th results from the quotient of the temperature difference ΔT and the heat flow Q _V. In the present invention, thermally conductive materials are to be understood in particular as those which have a thermal conductivity λ> 50 W / mK, in particular λ> 100 W / mK. In the present invention, however, heat-insulating materials are distinguished by a thermal conductivity λ <15 W / mK, in particular λ <3 W / mK.

According to the invention, a diameter d _{S of} the stack of layers is smaller than a diameter d _{K of} the piston head. The layer stack preferably has a diameter d _S which corresponds to more than 90%, preferably more than 95%, in particular more than 98% of the diameter d _K. On the one hand, this has the advantage that the layer stack and in particular the heat-conducting layer is not connected to the edge of the piston crown, in particular not to the top land, and via such a connection no heat conduction via the heat-conducting material of the second layer in the piston and beyond, for example in the cylinder material can take place. Another tribological advantage is in particular that the particularly hard layer stack does not come into contact with a running surface of the piston or liner.

According to the invention, the heat-insulating material of the first layer comprises an intermetallic compound. It could advantageously be shown that pistons which are coated with a stack of layers according to the invention are used as heat-insulating Materials have intermetallic compounds, have a particularly high thermal stability at temperatures> 500 ° C.

Intermetallic compounds, or intermetallic phases, are homogeneous chemical compounds made up of two or more metals. In contrast to alloys, they show lattice structures that differ from those of the constituent metals. In their lattice there is a mixed bond consisting of a metallic bond component and lower atomic bond or ion bond components, which can result in superstructures. According to the invention, the intermetallic compounds are based on iron aluminum, namely on FeAl (Cr, Nb, Zr, C, B) and / or Fe ₃ Al (Cr, Nb, Zr, C, B). That is, depending on the ratio of iron and aluminum to one another, the intermetallic compound is composed of 50% to 95% by weight of iron, in particular 70% to 95% by weight of iron and 5% to 50% by weight composed of aluminum, in particular from 5% to 30% by weight of aluminum. With a mass fraction of in total 0 to 10% by weight based on the total mass, the intermetallic compounds can contain contents of further alloying elements and impurities, in particular of chromium, niobium, zirconium, carbon and boron.

The intermetallic compounds used as heat-insulating material have in common that, in addition to a particularly high temperature resistance of over 500 ° C., they have a coefficient of expansion that is compatible with the piston material. This means that the volume expansion that a material experiences as a result of a temperature increase, in a layer stack in a preferred embodiment, is related between the heat-insulating material and the piston crown in such a way that the temperature prevailing on the heat-insulating material just expands this material to such an extent that it does not become one Delamination comes from the piston crown as a result of the increase in temperature of the layer stack. Thus, the service life of the stack of layers on the piston can be significantly increased by a suitable choice of the heat-insulating material.

In a further preferred embodiment of the invention it is provided that the thermally conductive material of the second layer comprises a metal and / or a thermally conductive ceramic, since these in particular have thermal conductivity values λ> 50 W / mK. In particular, it is preferred that the thermally conductive material comprises beryllium, aluminum, copper, silver, silicon, molybdenum, tungsten, carbon, beryllium oxide, beryllium nitrite, silicon nitrite and / or silicon carbide and mixtures and / or alloys thereof. As bulk material, these materials have a thermal conductivity λ> 100 W / mK. For example, the metal aluminum with a purity of 99.5% has a thermal conductivity λ = 236 W / mK, copper has a thermal conductivity λ = 401 W / mK and silver a thermal conductivity λ = 429 W / mK, while silicon carbide can achieve thermal conductivity of up to 350 W / mK. The materials mentioned are therefore particularly suitable for achieving a particularly rapid and uniform temperature distribution on the surface of the piston crown and thus preventing, in particular, locally limited temperature peaks. If temperature peaks nevertheless occur, that is to say local temperature maxima on the surface of the piston crown, the very high temperature prevailing there can be distributed very quickly over the entire surface of the piston crown and thus reduced. In this context, temperature peaks occur in particular when the temperature in areas of a surface suddenly increases by more than 50 ° C., in particular by more than 100 ° C. with respect to the mean surface temperature, and thus a high temperature gradient arises.

In a further embodiment of the invention it is preferred that an adhesion promoter layer is arranged between the surface of the piston crown and the first layer and / or between the first layer and the second layer. Adhesion promoters are substances that are used to increase the adhesive strength of composites directly and / or indirectly. In this case, the adhesive strength between the functional layer and the surface of the piston crown or between functional layers can be increased. The adhesive strength of coatings is defined as the measure of the resistance of a coating to its mechanical separation from the substrate. In the direct case this means that an improved adhesive strength of the functional layer on the surface of the piston crown or an improved adhesive strength of the second layer on the first layer leads to the fact that these can be separated from one another more difficultly by external influences. In this context, for example, the occurrence of strong temperature fluctuations can be understood as an external influence. If, for example, the arranged first layer expands more than the composite partner, that is to say, for example, than the light metal alloy or the second layer, then shear forces arise at the connection point. In addition, the adhesion promoter layer can act as a corrosion protection layer and thus indirectly increase the adhesive strength of the composite. The arrangement of an adhesion promoter can advantageously lead to an increase in the wettability of the substrate surface. In addition, an adhesion promoter can increase the formation of chemical bonds between the substrate surface and the layer. This is particularly the case when the two layers have very different physical properties with regard to their surface, such as polarity or lattice structure. Thus, the arrangement of an adhesion promoter between the piston crown and the first layer or between the first and second layer can Increase the durability and thus the service life of the stack of layers on the surface of the piston crown.

The adhesion promoter layer preferably comprises an Fe ₃ Al, FeAl, FeAl / Fe ₃ Al, NiCr, NiCrAl, NiCrAIY, FeCrAIY, CuCrAlY alloy and / or an intermetallic compound made of FeAl (Cr, Nb, Zr, C, B) and / or Fe ₃ Al (Cr, Nb, Zr, C, B).

The individual layers can have a gradient based on the layer composition. If, for example, individual layers are composed of mixtures and / or several components, the ratio of these to one another can vary within the relevant layer.

In a further embodiment, it is preferred that the piston head has a depression and the layer stack is arranged within the depression. In the present invention, a depression is to be understood as an area of the piston crown which is lower than a surrounding surface of the piston crown. A depression is therefore an indentation or also a depression within the piston head, which is designed to at least partially accommodate a stack of layers. The diameter or the width of the recess corresponds at least to the width or the diameter of the layer stack, so that the layer stack is preferably arranged in the region of the recess and is not in contact with the surface of the piston head beyond this region. The stack of layers is preferably arranged completely in the recess in the piston head and does not protrude above the surface level of the piston head, but is flush with the circumferential edge of the piston head. This ensures that the stack of layers does not affect the flow pattern on the surface of the piston crown. In an alternative embodiment it is provided that at least the second layer, that is to say the layer which comprises the thermally conductive material, protrudes from the recess and / or has a diameter which is smaller than the diameter of the recess. The advantage of this configuration is that the second layer and in particular the thermally conductive material are not in contact with the surface of the piston surface. Such contact would weaken the thermal insulation effect of the lower, i.e. the first, layer. The heat would be transferred to the piston crown via the heat-conducting layer and could be conducted out of the combustion chamber via the piston.

Another aspect of the invention relates to a piston machine having a piston according to the present invention. The piston machine according to the invention is characterized by a high degree of efficiency, efficient exhaust gas treatment and a very long service life of the individual components.

Further preferred embodiments of the invention emerge from the other features mentioned in the subclaims.

The various embodiments of the invention mentioned in this application can advantageously be combined with one another, unless stated otherwise in the individual case.

Figur 1

eine schematische Schnittdarstellung eines Kolbens in einer ersten Ausgestaltung der Erfindung,

Figur 2

eine schematische Schnittdarstellung eines Kolbens in einer zweiten Ausgestaltung der Erfindung und

Figur 3

schematisch einen Detailausschnitt eines erfindungsgemäßen Schichtstapels auf einem Kolbenboden gemäß Figur 2 oder 3.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

Figure 1

a schematic sectional view of a piston in a first embodiment of the invention,

Figure 2

a schematic sectional view of a piston in a second embodiment of the invention and

Figure 3

schematically shows a detail of a stack of layers according to the invention on a piston head according to FIG Figure 2 or 3 .

The invention is based on the in the Figures 1, 2 and 3 schematic representations shown are explained in more detail.

A preferred embodiment of the piston 10 according to the invention is illustrated in FIG Figure 1 shown. Figure 1 shows a cylindrical piston 10 of a reciprocating piston engine, not shown further. In this embodiment, the piston 10 has a cylindrically shaped piston skirt 14 on which a substantially planar circular piston head 11 is arranged. The piston 10 also has circumferential grooves which are designed to accommodate sealing elements, in particular piston rings. The piston 10 is preferably made from a light metal alloy 15. Aluminum alloys, in particular aluminum-silicon alloys, are particularly preferred. Iron compounds, i.e. steels, can also be used as piston material. In the embodiment shown, the piston head 11 has a recess 12 in which a stack of layers 20 is arranged. The diameter d _{S of} the stack of layers 20 essentially corresponds to the diameter of the recess 12. The diameter d _{S of} the stack of layers 20 is made _{smaller in comparison to the diameter d K of} the piston head 11. In the embodiment shown, the depth of the recess 12 corresponds to the height of the layer stack 20, so that it does not protrude from the recess 12 and does not protrude beyond the surface of the piston head 11. The layer stack 20 preferably ends flush with the edge surrounding the recess 12. A detailed structure of the layer stack 20 is shown in a detailed drawing described below in FIG Figure 3 explained in more detail.

In the Figure 1 The embodiment of a piston 10 shown is distinguished in its mode of operation in that a layer stack 20 functionalizes the surface of a piston head 11 in a large area.

Another preferred embodiment of a piston according to the invention is shown in FIG Figure 2 shown. The piston 10, also shown in a sectional drawing, is basically constructed in the same way as that in FIG Figure 1 The piston 10 shown here differs from the first embodiment in that the piston head 11 of the cylindrical piston 10 is not designed in a planar manner, but rather has a depression 13. On the piston crown 11 of the in Figure 2 A functional layer stack 20 is arranged as shown in the second embodiment of the piston 10. The piston head 11 has no recess for receiving the stack of layers 20. The stack of layers 20 has, as in FIG Figure 1 shown has a smaller diameter than the piston head 11. There is thus a distance between the layer stack 20 and the outer edge of the piston head 11. While maintaining a defined edge, the remaining area of the piston head 11 is completely covered by the layer stack 20, including the part of the piston head 11, which represents the trough 13. The circumferential edge of the piston head 11 preferably corresponds to less than 10%, in particular less than 5%, preferably less than 2% of the surface of the piston head 11.

The one in the Figures 1 and 2 The functional layer stack 20 shown has both heat-insulating and heat-conducting functions. This is done by the in Figure 3 Outlined structure of the layer stack is achieved. Figure 3 shows a layer stack 20 according to the invention, which is arranged on a light metal alloy 15. The light metal alloy 15 is preferably aluminum alloys, in particular aluminum-silicon alloys. An adhesion promoter 23 can optionally be arranged on this light metal alloy 15.

The layer of adhesion promoter 23 preferably comprises materials which increase the adhesive strength between light metal alloy 15 and first layer 21. For this purpose, materials are suitable which, on the one hand, increase the wettability of the light metal alloy 15 and, on the other hand, and in particular compensate for the structural differences between the light metal alloy 15 and the first layer 21. For this purpose, alloys based on iron and aluminum, in particular Fe ₃ Al, FeAl, FeAl / Fe ₃ Al, NiCr, NiCrAl, NiCrAlY, FeCrAlY, CuCrAlY alloys are preferred. In addition, intermetallic compounds based on iron aluminum are suitable as adhesion promoters. In particular, chromium and / or niobium and / or zirconium, carbon and / or boron are added to an alloy made of iron and aluminum. A suitable material, which is used, for example, in the aerospace industry, is a nickel-chromium-aluminum composition. Alternatively, adhesion promoters based on austenitic iron, nickel and cobalt alloys, as well as compounds alloyed with Cr, Al and Y (so-called MCrAlY layers) or with Hf, Ta or Si, can also be used. Suitable adhesion promoters are commercially available under the brand names Amdry® 365, Amdry® 386, Amdry® 995, Amdry® 962, Amperit® 415, Metco 443 or Sulzer Metco® 445.

The adhesion promoter 23 is applied much thinner than the following layers and preferably has thicknesses in the range from 0.1 mm to 0.2 mm, in particular between 0.1 mm and 0.15 mm.

A first layer 21 adjoins this adhesion promoter 23 or, alternatively, directly to the piston head. This first layer 21 consists of a material which has heat-insulating properties. Materials which have a thermal conductivity λ <15 W / mK, in particular λ <3 W / mK, are particularly preferred here. The heat insulating materials used are intermetallic compounds based on iron-aluminum alloys, namely FeAl and Fe ₃ Al, which can preferably comprise constituents added up to a maximum of 10% of the total mass of the coating. The added materials are preferably chromium, niobium, zirconium, carbon or boron. The thickness of the first layer 21 is adapted, depending on the material, to the ambient conditions, in particular the ambient temperatures of the piston 10, during operation. The first layer 21 preferably has a thickness in the range from 0.02 mm to 5 mm, in particular in the range from 0.1 mm to 1.5 mm.

A further layer of an adhesion promoter 24 is optionally arranged on the first layer 21. This adhesion promoter basically has the same properties as the optional between Adhesion promoter 23 arranged on the piston crown surface and the first layer. In principle, the adhesion promoter layers 23 and 24 can be designed identically in one embodiment, but they can also vary within the preferred limits described, in particular in the composition and thickness of the layers.

A further functional layer, the second layer 22, is arranged on the first layer 21 or on the adhesion promoter 24 arranged on this first layer 21. The second layer 22 comprises at least 70%, in particular at least 95%, preferably at least 98%, a thermally conductive material. This thermally conductive material is characterized by a thermal conductivity λ which is preferably> 50 W / mK, in particular> 100 W / mK. Materials suitable for this purpose are, in particular, metals such as beryllium, aluminum, copper, molybdenum and tungsten, but also silicon and carbon and compounds, in particular ceramics such as beryllium oxide, beryllium nitrite, silicon nitrite and silicon carbide. Mixtures and / or alloys of these elements or compounds can preferably also be used as the heat-conducting material of the second layer 22. Depending on the thermally conductive material used and in particular on the thermal conductivity λ achieved with it, the second layer 22 is preferably made thinner than the first layer 21.Preferred thicknesses of the second layer 22 are in the range between 0.1 mm and 1 mm, particularly preferably between 0 , 05 mm and 0.8 mm.

The individual layers 21, 22, 23 and 24 of the layer stack 20 are preferably applied by means of flame spraying or plasma spraying under vacuum, high-speed flame spraying or atmospheric plasma spraying or by means of chemical and / or electrochemical processes such as painting, electroplating or the like. It is useful here to sharply define the areas of the individual layers 21, 22, 23 and 24. This can be achieved on the one hand by a mold applied to the piston head 11 before the injection, on the other hand by a recess 12 present in the piston head 11 and / or by post-treating the applied layer stack 20, in particular by removing the outermost edge of the layer stack 20.

The layer stack 20 has a heat-insulating, in particular insulating, function due to the heat-insulating properties of the first layer 21. Due to the very low thermal conductivity λ of the insulating materials applied through the first layer 21, only a very small part of the heat in the combustion chamber is dissipated to the surface of the piston crown and from there out of the cylinder chamber. Rather, the heat remains within the combustion chamber and is therefore still available for combustion Available. As a result, a higher degree of efficiency is achieved in the combustion chamber than at lower temperatures. At the same time, the exhaust gases discharged from the combustion chamber also have a higher temperature, which ultimately benefits exhaust gas treatment. A pure thermal insulation layer on the surface of the piston crown 11 would, however, at the same time mean that the temperatures cannot be evenly distributed on the surface. Rather, areas with increased temperature peaks would form. By arranging a second layer 22, which consists of material that has a very high thermal conductivity λ, the temperature from areas of temperature peaks is evenly distributed over the entire area of the layer stack 20. The optionally usable layers of adhesion promoters 23 and 24 increase the adhesive strength and corrosion resistance of the layer stack 20 on the light metal alloy 15 or between the first layer 21 and the second layer 22 and thus the service life of the layer stack 20.

List of reference symbols

10

piston

11

Piston crown

12th

deepening

13th

trough

14th

Piston skirt

15th

Light alloy

20th

Layer stack

21

first layer

22nd

second layer

23

Adhesion promoter

24

Adhesion promoter

Claims (6)

1. Piston (10) for a piston machine, wherein the piston (10) is composed in certain regions of a steel or a light metal alloy (15) and comprises a layer stack (20) arranged on a piston crown (11) of the piston (10), wherein the layer stack (20) at least comprises:

   - a first layer (21) which indirectly or directly adjoins a surface of the piston crown (11) and which comprises a heat-insulating material,

   - a second layer (22) which indirectly or directly adjoins the first layer (21) and which comprises a heat-conducting material,

   wherein a diameter (d_S) of the layer stack (20) is smaller than a diameter (d_K) of the piston crown (11),
   characterized in that the heat-insulating material of the first layer (21) comprises an intermetallic compound composed of FeAI(Cr, Nb, Zr, C, B) and/or Fe₃Al(Cr, Nb, Zr, C, B).
2. Piston (10) according to Claim 1, characterized in that the heat-conducting material of the second layer (22) comprises Be, Al, Cu, Ag, Si, Mo, Wo, C, BeO, BN, SiN and/or SiC, and mixtures and/or alloys of these.
3. Piston (10) according to any of the preceding claims, characterized in that an adhesion promoter layer (23, 24) is arranged between the light metal alloy (15) and the first layer (21) and/or between the first layer (21) and the second layer (22).
4. Piston (10) according to Claim 3, characterized in that the adhesion promoter layer (23, 24) comprises an Fe₃Al alloy, FeAl alloy, FeAl/Fe₃Al alloy, NiCr alloy, NiCrAI alloy, NiCrAlY alloy, FeCrAlY alloy, CoCrAlY alloy and/or an intermetallic compound composed of FeAI(Cr, Nb, Zr, C, B) and/or Fe₃Al(Cr, Nb, Zr, C, B).
5. Piston (10) according to any of the preceding claims, wherein the piston crown (11) has a depression (12), and the layer stack (20) is arranged within the depression (12).
6. Piston machine having a piston (10) according to any of Claims 1 to 5.

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