EP3008317A1

EP3008317A1 - Method for producing an oxidation protection layer for a piston for use in internal combustion engines and piston having an oxidation protection layer

Info

Publication number: EP3008317A1
Application number: EP14732527.8A
Authority: EP
Inventors: Herbert MÖDING; Thomas Steffens; Leander Schramm
Original assignee: KS Kolbenschmidt GmbH
Current assignee: KS Kolbenschmidt GmbH
Priority date: 2013-06-14
Filing date: 2014-06-13
Publication date: 2016-04-20
Also published as: US20160138516A1; CN105431624B; CN105431624A; DE102014211366A1; WO2014198896A1; MX2015016390A

Abstract

The invention relates to a piston (1), especially a steel piston for an internal combustion engine, comprising a piston head (2) which forms part of a combustion chamber (3), at least the piston head (2) having an oxidation protection layer. The invention further relates to a method for producing an oxidation protection layer.

Description

DESCRIPTION

Method for producing an oxidation protection layer for a piston for use in internal combustion engines and pistons with an oxidation protection layer

The invention relates to a method for producing an oxidation protection layer for at least the region of the piston crown of a steel piston for internal combustion engines and a piston with an oxidation protective layer, according to the features of the respective preamble of the independent claims.

A forged piston is known for example from DE 103 1 1 150 A1. There, the piston is described from a first blank having at least one flat end face made of oxidation-resistant steel and a second cylindrical blank having at least one flat face made of hot forme steel. The two blanks are formed by forging to a piston blank. The finished piston thus exists in the region of the piston head to the first piston ring groove of the oxidation-resistant steel.

The prior art discloses the use of oxidation resistant steels for the combustion chamber region of pistons.

The object of the invention is to ensure the protection of the combustion chamber area of steel pistons from oxidation processes or at least significantly improve. This object is achieved by a method and a piston with the features of the independent claims.

The oxidation protection layer according to the invention achieves the avoidance of oxidation processes in engine operation and improved thermal shock resistance. The result is a quasi-monolithic piston.

An oxidation protection layer is produced, for example, by physical deposition of the coating materials from the gas phase (Physical Vapor Deposition - PVD). generated. Here, the coating materials are transferred by physical processes in the gas phase from which they are then deposited later on the substrate. While in a method for depositing an oxidation protection layer on the surface of a piston for internal combustion engines according to the PVD technique, the coating material is usually evaporated in solid form and optionally by supplying heat, the supply is carried out in the CVD technique in the gas phase.

Alternatively or additionally, as a method for depositing an oxidation protective layer on the surface of a piston, the chemical vapor deposition can be used (Chemical Vapor Deposition - CVD). In this method of surface coating technology, the coating materials are converted into the vapor phase with the aid of chemical processes, from which they are then deposited on the substrate. The coating of the combustion chamber region as a substrate can be achieved, for example, with prior bonding layer-free gas or plasma nitriding. In this case, layer thicknesses of 3-20 pm are sought, preferably, layer thicknesses of 5 pm are desired. Furthermore, coating materials Al-Cr-Ti nitrides (aluminum-chromium-titanium-nitrides) or carbides which have a high thermal shock resistance can be used. By deposition of the coating materials from the gas or vapor phase on the piston surface homogeneous defined oxidation protective layers can be produced.

Alternatively, the deposition of the oxidation protection layer on the piston surface can also take place with the aid of pulsed laser deposition (PLD). In this method, high-energy and short-wave (UV) light is used to bring the starting material (solid target) in the gas phase and above it in the form of a layer on the piston surface to be coated (substrate). Laser ablation also belongs to the class of physical vapor deposition (PVD) processes.

The application of oxidation protective coatings on the piston surfaces can alternatively also by the Plasmaimpax ^® process. This uses high-energy particles and a high-voltage pulse technique to dimensional modification and coating of surfaces. The Plasmaimpax method enables a layer deposition via plasma sources in a vacuum from the gas phase. It is a hybrid technique of plasma activated low temperature CVD and ion implantation. To increase surface hardness, wear and corrosion resistance, this environmentally friendly technology enables ion implantation processes and ion-assisted coating processes. Even lower coating temperatures are sufficient to successfully apply layer deposition and surface modification.

With the Plasmaimpax technology, diamond-like carbon (DLC) protective coatings can be applied and, on the other hand, surface modification by ion implantation to increase surface hardness. The diamond-like carbon layers have a high chemical resistance (corrosion resistance).

The deposition of the oxidation protection layer on the piston surface can alternatively also be carried out by a plasma assisted chemical vapor deposition (PECVD or PACVD - Plasma Assisted (Enhanced) Physical Vapor Deposition) method. For example, can be supplied to produce carbon layers acetylene (C ₂ H ₂ ) or silicon-containing layers HMDSO (hexa-methyl disiloxane), which is cracked in the plasma and thus provided for coating. Low processing temperatures are possible with the PACVD technology.

For the purposes of this document, the following methods for producing an oxidation protection layer on the surface of a piston for internal combustion engines are summarized under physical processes for the deposition of the coating materials from the gas phase (Physical Vapor Deposition - PVD), the classical PVD and the pulsed laser ablation (PLD - Pulsed Laser deposition). (Chemical Vapor Deposition - CVD) For the purposes of this document, the process mentioned below for producing an oxidation protection layer on the surface of a piston for internal combustion engines by method for chemical vapor deposition are summarized Plasmaimpax ^® - method and plasma-enhanced chemical vapor deposition.

Alternatively or additionally, galvanic coatings with nickel, nickel-base alloys, chromium, chromium-base alloys, scale-resistant Fe-base alloys (iron-based alloys) or tungsten and molybdenum alloys are used to form an oxidation protection layer. In the electroplating layer thicknesses of 5-100 μιη are deposited, preferably 5 - 20 μιτι deposited on the substrate.

Under electroplating process to produce an oxidation protective layer on the surface of a piston for internal combustion engines is the electrochemical deposition of metallic precipitates (coatings) on substrates (objects), it forms a galvanic coating on the piston or the piston surface. Electroplating processes belong to the methods of electrochemical deposition (ECD). The ECD methods alternatively serve to create an oxidation protection layer on the surface of a piston for internal combustion engines. Electrochemical metal deposition can reliably produce metal layers on the piston surface as an oxidation protection layer. Galvanic methods are suitable for the formation of oxidation protection layers, due to relatively low expenditure on equipment.

Alternatively or additionally, plating methods can be used as a method for producing an oxidation protection layer on the surface of a piston for internal combustion engines. During plating, at least two materials are joined by plastic deformation under pressure. At least one material forms the oxidation protection layer on the piston surface. Alternatively or additionally, an oxidation protective layer is applied by application of a layer by thermal spraying (plasma, HVOF, flame spraying processes), which is compressed as required (adhesion, gas tightness) by means of electron beam, TIG process, etc., and metallurgically bonded (material groups similar to those of US Pat galvanic coating) formed on the substrate. Steels with high chromium, silicon and aluminum contents (Cr, Si and Al contents) form very dense oxide layers that protect the material from further oxidation.

Methods of thermal spraying may alternatively be used to create an oxidation protection layer on the surface of a piston for internal combustion engines.

Thermal spraying is a universally applicable

Surface coating method in which a usually powdered or wire-shaped coating material with high thermal and / or kinetic energy is spun on a component surface and forms a layer there. With a variety of available process variants, a wide range of materials such as metals and ceramics, but also high-performance polymers can be processed into technical coatings. The layer thicknesses range from approx. 30 m to several millimeters.

Thermal spraying includes the following methods for producing an oxidation protection layer on the surface of a piston for internal combustion engines. Wire or bar flame spraying, powder flame spraying, plastic flame spraying, high velocity oxygen fuel (HVOF), detonation or flame shock spraying, plasma spraying, laser spraying, arc spraying, Cold gas spraying and Plasma Transfer Welding (PTA).

Thermal spraying methods can be used with a variety of coating materials, so that in the short term the oxidation protection layer on the piston crown can be varied according to the respective requirements. In wire or rod flame spraying, the spray additive is melted continuously in the center of an acetylene-oxygen flame. With the help of a nebulizer gas, such as compressed air or nitrogen, the droplet-shaped spray particles are detached from the melting area and thrown onto the prepared piston surface.

In powder flame spraying, the pulverulent spray additive is melted or melted in an acetylene-oxygen flame and thrown onto the prepared piston surface with the aid of the expanding combustion gases.

If necessary, an additional gas such as argon or nitrogen can also be used to accelerate the powder particles. The variety of spray additives is very wide-ranging in powders with well over 100 materials.

The powders distinguish between self-fluxing and self-adhering powders. Self-fluxing powders usually require additional thermal treatment. This "smelting" takes place predominantly with acetylene-oxygen burners. If a thermal aftertreatment takes place, it is a multi-stage process for the method for producing an oxidation protective layer on the surface of a piston for internal combustion engines.

Due to the thermal process, the adhesion of the sprayed layer on the base material is considerably increased, the sprayed layer becomes gas- and liquid-tight.

The plastic flame spraying differs from the other flame spraying process in that the plastic additive does not come into direct contact with the acetylene-oxygen flame. In the middle of the flame spray gun is a powder delivery nozzle. This is enclosed by two annular nozzle outlets, the inner ring being air or an inert gas and the outer ring being the thermal energy carrier, the acetylene-oxygen flame. The melting process of the plastic is thus not directly by the flame, but by the heated air and radiant heat.

By flame spraying or powder flame spraying, for example, metal powder, metal powder alloys, ceramic powder and plastic powder can be processed.

The NiCrBSi coating (nickel-chromium-boro-silicon coating) is a flame-spraying surface refinement to increase the oxidation resistance of the piston surface. A coating of NiCrBSi alloy is very corrosion resistant.

The nickel content in the coatings is between 40-90%. The chromium content in the coating is between 3-26% and gives the layers their hardness.

The NiCrBSi coating is applied, for example, by powder flame spraying with subsequent melting / sintering.

As base materials, steel and stainless steels are processed. The components are, for example, stress annealed, coarsely blasted and immediately coated in order to avoid undercutting.

The NiCrBSi powder is sprayed with a flame spray gun and then melted with an autogenous hand torch, inductive or in a vacuum oven at about 1000 C.

As a "wet glow", the NiCrBSi coating is visible during the melting process. This "wet glow" is very plastic in the state at about 1000 ° C and is therefore designed so that the melt does not run down or drip from the component and thus the NiCrBSi coating would be faulty.

This high-tech NiCrBSi coating technology is the only one of the thermally sprayed spray coatings without additional sealing techniques gas-tight and is also best against shock load due to diffusion into the base material of all flame spray coatings suitable.

With the additive WC / Ni, the hard metal coating (NiCrBSi coating) becomes significantly more corrosion resistant, whereby WC / Co has a higher temperature resistance.

Also PTFE or graphite can be added to the alloy. As a result, this hard metal coating achieves improved non-stick and sliding properties.

In high-velocity flame spraying (HVOF), continuous gas combustion takes place at high pressures within a combustion chamber, in the central axis of which the pulverulent spray additive is supplied. The high pressure generated in the combustion chamber of the fuel gas-oxygen mixture and the mostly downstream expansion nozzle produce the desired high flow velocity in the gas jet. As a result, the spray particles are accelerated to the high particle speeds, which lead to enormously dense spray coatings with excellent adhesive properties. Due to the sufficient but moderate temperature introduction, the spray additive process causes only slight metallurgical changes in the spray additive material, e.g. minimal formation of mixed carbides. In this process, extremely thin layers with high dimensional accuracy can be produced.

Propane, propene, ethylene, acetylene and hydrogen can be used as combustion gases.

For example, carbide materials may be applied to the surface of a piston for internal combustion engines by high speed flame spraying (HVOF) as a method of forming an oxidation protection layer. The layers forming on the piston surface are very dense. Due to the high hardness of the carbide layers, they provide excellent protection against wear and oxidation for the piston. For example, the following materials are used: chromium carbides (Cr ₃ C ₂ , Cr ₃ C ₂ / NiCr) or tungsten carbides (WC / Co, WC / Ni, WC / Co / Cr). Detonation spray or flame shock spray is an intermittent spray process. The so-called detonation gun consists of an outlet pipe, at the end of which there is a combustion chamber. In this, the supplied acetylene-oxygen spray powder mixture is detonated by a spark. The shock wave generated in the tube accelerates the spray particles. These are heated in the flame front and spin at high particle velocity in a directional beam onto a prepared piston surface. After each detonation, a cleaning purge of the combustion chamber and the tube is carried out with nitrogen.

In the case of plasma spraying, the pulverulent spray additive in or outside the spray gun is melted by a plasma jet and thrown onto the piston surface. The plasma is generated by an arc burning in argon, helium, nitrogen, hydrogen or in the mixture of these gases. The gases are dissociated and ionized, they reach high outflow velocities and emit their heat energy to the spray particles during recombination. This produces a plasma flame with a temperature of up to 20,000 ° C. The arc is generated between the electrode and the nozzle. Due to the high temperatures in particular ceramic materials can be processed.

The arc is not transmissive, that is it burns within the spray gun between a centrally disposed electrode (cathode) and the anode forming water-cooled spray nozzle. The process is applied in normal atmosphere (APS - Atmospheric Plasma Spraying), in the protective gas stream, that is in an inert atmosphere such as argon, under vacuum and under water. A specially shaped nozzle attachment can also be used to generate high-speed plasma.

Ceramic coatings are mainly applied to the surface of the piston with the help of atmospheric plasma spraying (APS). Spraying materials are used for coating piston surfaces, for example based on aluminum oxide (Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium oxide (TiO ₂ ) and zirconium oxide (ZrO ₂ ).

In the laser spraying process, a powdered spray additive is introduced into the laser beam via a suitable powder nozzle. With the help of laser radiation, both the powder and a minimal part of the piston surface (micro-area) are melted and the supplied spray additive metallurgically connected to the base material, the piston surface. To protect the molten bath is a protective gas.

In the arc spraying process, two wire-shaped spray additives of the same or different types are melted in an arc and spun onto the prepared piston surface by means of atomizing gas, for example compressed air. Arc spraying is a high-performance wire spraying process in which only electrically conductive materials can be sprayed.

When using nitrogen or argon as a sputtering gas oxidation of the materials is largely prevented.

Metallic materials are applied, for example, by arc spraying on the piston surface. The conceivable range of materials includes most metals and very many mixtures, for example aluminum, copper (Cu / Al, Cu / Al / Fe), nickel (Ni / Al, Ni / Cr), molybdenum and zinc (Zn / Al).

The cold gas spraying process is similar to high speed flame spraying. The kinetic energy, ie the particle velocity, is increased here and the thermal energy is reduced. Thus, it is possible to produce almost oxide-free sprayed coatings. This process has become known as CGDM (Cold Gas Dynamic Spray Method).

The oxidation protection layer may also be applied to the piston surface by the metal coating system Cold Metal Spray or Cold Spray System. The spray additive material is accelerated with the aid of a gas jet heated to about 600 ° C. with appropriate pressure to particle velocities> 1 000 m / s and brought to the piston surface to be coated as a continuous spray jet.

Studies have shown that layers produced by this process have extreme bond strengths and are extremely dense. While in the usual methods of thermal spraying, the powder must be heated in the injection process to above its melting temperature, it is heated in the cold gas spraying only to a few hundred degrees. The oxidation of the spray material and the oxide content of the sprayed layer are thus significantly lower. Coated substrates show no material changes due to the effect of heat.

Plasma deposition welding (PTA) with powder under transferred arc. In the PTA process, the piston surface is melted. A high-density plasma arc serves as a heat source and metal powder is used as a coating material. The arc forms between a permanent electrode and the workpiece. In the transferred arc, the plasma is generated in a plasma gas, for example argon, helium or argon-helium mixtures, between the central tungsten electrode (-) and the water-cooled anode block. The powder is brought by means of a carrier gas to the burner, heated in the plasma jet and applied to the piston surface. Here it melts completely in the molten bath on the substrate.

The whole process takes place in the atmosphere of a protective gas, for example argon or argon-hydrogen mixture.

The PTA process allows low mixing (5-10%), a small heat-affected zone, a high application rate (up to 20 kg / h), true metallurgical adhesion between the substrate and the layer - thus completely dense layers - and flexibility of the alloying elements.

The predominantly used hardfacing powders can be classified as nickel base, cobalt base and iron based alloys. Alternatively or additionally, an oxidation protection layer is formed by laser deposition welding on the piston surface, the substrate. The material to be applied is fed to the process as powder, wire or strip. The surface of the material to be coated is melted. It can be applied almost any material, examples of self-fluxing alloys (NiCrBSi), nickel-based alloys such as NiWC (nickel-tungsten) or Deloro Steinte ^®. With its components cobalt, chromium, molybdenum, tungsten and nickel, Steinte ^{® is} extremely resistant to corrosion, wear and heat. A larger dissolved chromium content in the alloy also increases the corrosion resistance and thus also the oxidation resistance of the piston surface. In this case, layer thicknesses between 20 and 300 pm are applied. The layers usually do not have to be reworked. A substrate pretreatment, for example by abrasive blasting processes such as corundum blasting is not necessary.

Laser deposition welding with filler materials in powder and wire form is also referred to as Direct Metal Deposition (DMD) or Laser Metal Deposition (LMD).

Alternatively or additionally, the oxidation protection layer is produced by cold gas spraying on the substrate, in this process the material to be sprayed is supplied in powder form. The layers are very dense and the particles are hardly oxidized during the coating. Almost any material can be applied, such as titanium and titanium alloys, but also nickel-base alloys, c-BN (cubic boron nitride, β-boron nitride) with NiCrAI (nickel-chromium-aluminum), NiCr (nickel-chromium), NiAl (nickel-aluminum) , CuAl (aluminum bronze) or MCrAIY powder. Typical layer thicknesses are in the range of 20-300 pm. During coating, the component is hardly heated. CBN is the second hardest diamond after diamond. In contrast to diamonds, CBN does not release carbon to steel under the influence of temperature, which makes it particularly suitable for surface coating of steel pistons. MCrAIY superalloys (metal chromium aluminum yttrium; M = metal, for example, nickel (Ni) or cobalt (Co)) are high-temperature alloys that undergo selective oxidation. Form oxide layers and thus form an oxidation protection on the piston surface. Nickel Cobalt Chrome Aluminum Yttrium (NiCoCrAIY) or Cobalt Nickel Chrome Aluminum Yttrium (CoNiCrAIY) materials provide good resistance to oxidation.

Furthermore, the application of a layer, in particular an oxidation protection layer in a further embodiment by thermal spraying (plasma, HVOF, arc, flame spraying processes) is carried out. Here, the coating material is supplied as powder, wires, suspensions or rods. The coating composition can be carried out as a single-layer layer based on the coating material (monolayer layer). The use of different coatings or the combination of different coating materials such. a primer (e.g., NiCr, NiAl) which also provides hot gas corrosion protection (MCrAIY) and a thermal barrier coating (TBC) such as yttria-stabilized zirconia (Y-ZrO) may result in a multilayer coating construction.

Thermal barrier coatings (TBCs) reduce heat transfer and insulate the substrate. The layer systems deposited on piston surfaces preferably consist of two components. A bonding layer that acts as an oxidation barrier and consists of a metallic material, such as MCrAIY. As well as a cover layer of a ceramic material, for example yttrium-stabilized zirconium oxide (YSZ).

Depending on the coating method, it is also possible to apply Ni-base alloys or MoSi ₂ / SnAI (molybdenum silicon dioxide / zinc aluminum). The layers can be compacted as required (adhesion, gas tightness) by means of electron beam, TIG process, diffusion annealing, induction annealing, laser, etc., and metallurgically bonded (material groups similar to the galvanic coating). Steels with high Cr, Si and Al contents (chromium, silicon and aluminum contents) form very dense oxide layers which protect the material from further oxidation. The typical layer thicknesses are here in the range of 20 - 300 pm. The W IG process (tungsten inert gas welding) is a

Inert gas welding process, as protective gas inert inert gases are used. During the welding process, an arc burns between the workpiece and a non-consumable tungsten electrode, which melts the base material and the filler material.

Welding processes can be implemented with a manageable outlay on equipment in order to apply oxidation protection layers to piston crowns. For example, laser deposition welding methods or tungsten coating methods are suitable.

Inert gas welding process for the production of oxidation protection layers due to the low equipment cost.

The diffusion annealing serves to eliminate or reduce concentration differences, for example, crystal segregations or structural heterogeneities in the piston or the piston surface. Based on the principle that high temperatures favor diffusion. Annealing takes place at temperatures between 1000 ° C and 1200 ° C. The homogenization of the piston surface increases its oxidation resistance.

Induction annealing or induction hardening brings especially complicated shaped workpieces, such as pistons or piston surfaces only in certain areas to the required hardening temperature (partial hardening), to then quench them.

Annealing process contribute in particular to the homogenization of the oxidation protection layer and are therefore combinable with other processes mentioned in this document, for example, diffusion annealing or induction annealing are particularly suitable for homogenization of the oxidation protective layer and are therefore individually applicable but also in combination with other methods for producing an oxidation protective layer ,

It is also possible to impregnate or seal the layers after spraying. This is a Siegler aufacht, which then in the Cavities in the spray layer penetrates and closes and thus prevents crevice corrosion or undercutting.

Alternatively or additionally, the use of coatings of aluminum or aluminum alloys, preferably with the alloying elements silicon (eg AISi-12), copper and / or magnesium, provided by formation of iron aluminides and / or stable to form an oxidation protective layer Iron-aluminum mixed oxides (preferably of the spinel type, eg Hercynit FeO Al ₂ 0 or FeAl ₂ ⁿ 4 or Pleonast MgAl ₂ 0 ₄ ) form oxidation-resistant protective layers with layer thicknesses of 5 to 200 μm. The order of the aluminum (or the aluminum alloy) on the piston head can be carried out by one of the methods described above, by a dip bath (Alfinbad) or by the application of an aluminum-containing paint or a suspension. Depending on the application method may be achieved by subsequent, targeted, brief heating of the piston head - preferably to temperatures greater than 660 ° C (AI melting point) - an improved layer formation and adhesion under certain circumstances. This heating can be done for example by laser treatment, inductive heating, by a gas burner or the like, the access of oxygen or in the simplest case of atmospheric oxygen supports the formation of protective, stable mixed oxides.

In a particularly advantageous manner, the oxidation protection layer is produced by coatings of, in particular, pure aluminum or aluminum alloys. Such an alloy may, for example, form iron aluminides and / or stable iron-aluminum mixed oxides (preferably of the spinel type). The order of the aluminum or the aluminum alloy on the piston head can be carried out according to one of the methods described above or by a dip bath (Alfinbad) or by the application of an aluminum-containing paint or a suspension.

The Alfin method provided alternatively to the formation of an oxidation protection layer on the surface of a piston for internal combustion engines is a composite casting method for metal joining of steel or cast iron with aluminum or aluminum alloys. This Al-Fin process is used for composite casting of aluminum (AI) and alloys with steel or cast iron. The to be connected Piston components are first cleaned, preheated in a salt melt and immersed in liquid aluminum (830 to 880 ° C). The formed intermetallic iron-aluminum layer is firmly connected to the base material and facilitates alloy formation and adhesion in the subsequent encapsulation with aluminum materials as oxidation protection layer. The Al-Fin process allows a particularly good bond between iron and aluminum alloys.

The coatings of aluminum or at least one aluminum alloy are produced at least on the piston head of the piston by a previously described method, by a dip bath (Alfinbad), by the application of an aluminum-containing paint and / or a suspension.

The generation of a metallic bond between the substrate and the deposited layer can be effected by an additional thermal application in a second method step, for example by means of laser, TIG, electron beam or inductively.

When an oxidation protection layer is formed on the surface of a piston, a step of preparing the surface may be preceded. The preparation of the piston surface can be done by cleaning and / or pretreatment. During cleaning, impurities are removed from the piston surface without influencing the absorbent material. By contrast, the pretreatment serves to optimize the efficiency of the processes for producing an oxidation protection layer on the piston surface. For the pretreatment, processes may be used which treat the corresponding piston surface in such a way that their surface properties improve, for example with regard to the adhesion of the oxidation protection layer. A material-altering pretreatment is also called activation. For example, for this purpose, the piston surface is roughened to allow the surface enlargement or the resulting undercuts a Mikroverklammerung the oxidation protection layer and to increase the mechanical adhesion. Furthermore, the surface energy can be increased, this is also referred to as increasing the specific adhesion. The preparation of the piston surface can be carried out by abrasive mechanical methods such as grinding, brushing or blasting. In these methods, a part of the piston surface can be removed. At least this removed part of the piston surface to be coated can be rebuilt by the oxidation protection layer to be produced according to a method mentioned in this document.

The preparation of the piston surface can also be done by chemical pretreatment methods such as etching or pickling.

Furthermore, the preparation of the piston surface can also be done by physical methods such as flame, plasma, corona, or laser pretreatment.

In the preparation of the piston surface for applying at least one method mentioned in this document for generating an oxidation protective layer by cleaning, for example, impurities from the previous production steps (for example forming process) such as coolants and / or lubricants (KSS), corrosion protection oils, flux, scale, graphite , Metallic soaps, sulfonates, mineral oils, inorganic soaps, metal oxides, metal salts, dust and / or shavings.

The production of an oxidation protection layer according to one of the methods mentioned in this document can be carried out on a piston blank, a region of the piston or on the entire surface of the piston for an internal combustion engine. Preferably, at least the piston head has an oxidation protection layer.

All of the methods mentioned in this document for producing an oxidation protection layer on the surface of a piston for internal combustion engines can be used individually or in virtually any combination for producing an oxidation protection layer on the surface of a piston for internal combustion engines. By combining methods for producing an oxidation protection layer on the surface of a piston for internal combustion engines For example, multilayer systems can be deposited on the surface of a piston.

By forming the oxidation protection layer as a multilayer system on the piston surface, the requirements for the oxidation protection layer can be taken into account.

In carrying out the oxidation protection layer on the piston surface as a multilayer system, favorable materials can be used as the basis for the piston.

When designing the oxidation protection layer as a multilayer system, at least two layers are applied to the piston surface. These at least two layers can have the same properties chemically and physically, but they can also have chemically and / or physically differing properties.

The methods for producing an oxidation protection layer can be used individually or in virtually any combination. The combination of processes can result in multilayer oxidation protection layers. These multi-layer oxidation protection layers may consist of identical substances or different substances.

According to the invention, in the case of a piston, in particular a steel piston for an internal combustion engine, having a piston crown which is part of a combustion chamber, at least the piston crown has an oxidation protection layer.

By applying an oxidation protective layer on the piston crown, the oxidative attack on the piston material in the region of the combustion bowl is reduced or even avoided. It is thus possible to manufacture the piston from other materials. By choosing a different material, the costs can be reduced. The aforementioned coating materials and classes of substances can be selected according to the requirements of the oxidation protection layer. Also, combinations of the various coating materials and classes are possible to form a suitable oxidation protection layer on the surface of the piston crown.

The invention will be further clarified with reference to the figure described below.

FIG. 1 shows a steel piston which has a coating according to the invention in FIG

Form has an oxidation protection layer.

In the following description of the figures, terms such as top, bottom, left, right, front, back, etc. refer exclusively to the example representation and position of the device and other elements selected in the figure. These terms are not intended to be limiting, that is to say that different positions and / or mirror-symmetrical design or the like may change these references.

FIG. 1 shows a piston 1 made of steel. The piston 1 has a piston head 2, which is part of a combustion chamber 3. Furthermore, the piston 1 has a top land 4 and a ring field 5. The ring field 5 is followed by a shaft 7 with a hub 6 at the bottom. The piston 1 is provided in the region of the piston head 2 with an oxidation protection layer according to the invention.

The use of the oxidation protection layer according to the invention is not limited to the design exemplified here of a piston for an internal combustion engine, but rather any piston plates can be provided with an oxidation protective layer according to the invention. LIST OF REFERENCE NUMBERS

1 piston

2 piston bottom

3 combustion chamber

4 lancet

5 ring field

6 hub

7 shaft

Claims

PATENT APPLICATIONS

1 . Method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protection layer by a physical process for the deposition of the coating materials from the gas phase (Physical Vapor Deposition - PVD) at least on a piston head (2) of the piston ( 1) is generated.

2. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer by a method for chemical vapor deposition (CVD) at least on a piston head (2) of the piston (1) generated becomes.

3. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer at least on a piston head (2) of the piston (1) by a method of electrochemical metal deposition (ECD - Electrochemical Deposition) is generated ,

4. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer by a thermal spraying process at least on a piston head (2) of the piston (1) is generated.

5. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protection layer by a Laserauftragschweiß- or tungsten Inertgasschweißverfahren at least on a piston head (2) of the piston (1) is generated.

6. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer by a Diffusionsglüh- or Induktionsglühverfahren at least on the piston head (2) of the piston (1) is generated.

7. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer is produced by coatings of aluminum or of at least one aluminum alloy on a region of the piston (1).

8. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, according to claim 7, characterized in that the aluminum alloy iron aluminides and / or stable iron-aluminum mixed oxides, these preferably of the spinel type, formed.

9. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, according to claim 7 or 8, characterized in that the coatings of aluminum or at least one aluminum alloy at least on the piston head (2) of the piston (1 ) are produced by a method according to claims 1 to 6, by a dip bath (Alfinbad), by the application of an aluminum-containing paint and / or a suspension.

10. A method for producing a piston (1), in particular a steel piston for an internal combustion engine, characterized in that an oxidation protective layer is produced by the combination of at least two methods according to claims 1 to 9.

1 1. Piston (1), in particular steel piston for an internal combustion engine, comprising an oxidation protective layer at least in the region of the piston head (2), characterized in that the oxidation protection layer is produced according to at least one method according to claims 1 to 10.

12. Piston (1) according to claim 1 1, characterized in that the

Oxidation protection layer is formed from the substance class of nitrides or carbides.

13. Piston (1) according to claim 1 1 or 12, characterized in that the

Oxidation protection layer of nickel, nickel-based alloys, chromium, chromium-based alloys, scale-resistant iron-based alloys or tungsten and molybdenum alloys is formed.

14. Piston (1) according to claim 1 1, 12 or 13, characterized in that the

Oxidation protection layer consists of a NiCrBSi coating (nickel-chromium-boron-silicon coating).

15. Piston (1) according to claim 1 1, 12, 13 or 14, characterized in that the oxidation protective layer of oxides, in particular aluminum oxide (Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), titanium oxide (TiO ₂ ) or zirconium oxide (ZrO ₂ ) consists.

16. piston (1) according to claim 1 1, 12, 13, 14 or 15, characterized in that the oxidation protection layer of a nickel-based alloys, in particular NiWC (nickel-tungsten carbide), NiCrAI (nickel-chromium-aluminum), NiCr (nickel-chromium ) NiAl (nickel-aluminum) or Steinte ^® with its components cobalt, chromium, molybdenum, tungsten and nickel.

17. piston (1) according to claim 1 1, 12, 13, 14, 15 or 16, characterized in that the oxidation protection layer of CBN or MCrAIY is formed.

18. piston (1) according to claim 1 1, 12, 13, 14, 15, 16 or 1 7, characterized in that the oxidation protection layer is formed of two layers of a thermal barrier coating (TBC), in particular formed from MCrAIY and a cover layer of a ceramic material, in particular of yttrium-stabilized zirconium oxide (YSZ).

19 piston (1) according to claim 1 1, 12, 13, 14, 15, 16, 17 or 18, characterized in that the oxidation protection layer consists of a MoSi ₂ / SnAI (molybdenum silica / zinc aluminum) layer.

20. piston (1) according to claim 1 1, 12, 13, 14, 15, 16, 17, 18 or 19, characterized in that the oxidation protective layer is formed of coatings of aluminum or at least one aluminum alloy, preferably with the alloying elements Silicon (eg AISi- ₁₂ ), copper and / or magnesium, which by forming iron aluminides and / or stable iron-aluminum mixed oxides (preferably of the spinel type, eg Hercynit FeO AI ₂ O ₃ or FeAI ₂ 0 ₄ or pleonast MgAl ₂ O ₄ ) form oxidation-resistant protective layers.

21. Piston (1) according to any one of claims 1 1 to 20, characterized in that the oxidation protective layer preferably has a thickness between 3 pm and 300 μητι.

22 piston (1) according to one of claims 1 1 to 21, characterized in that the piston (1) has a multi-layer oxidation protection layer of at least two oxidation protective layers according to claims 1 1 to 21.