EP2009132A1 - Method for manufacturing a functional layer, coating material, method for its manufacture and functional layer - Google Patents

Abstract

In a first stage (100) a foamable coating material (3), comprising a metal powder and a foaming agent, is coated as a layer (1') onto the substrate (2). In a second stage, heat is introduced, converting the layer into a foamed metal coating (1). The layer is applied by thermal spraying, especially using cold gas spraying. It is alternatively applied using electrophoretic deposition. Heat is introduced in a furnace; through electromagnetic radiation or using electromagnetic induction. The coating material is a high-nitrogen steel, the percentage of nitrogen contained being no more than 4 wt%, preferably 1-3 wt%. The nitrogen is at least partially released on heating, foaming the metal. To make the coating material, a metal is prepared as a powder. The metal has a given viscosity when molten. The powder is mixed with the foaming agent or propellant, which is able to release gas for foaming. The mixture contains no more than 5 wt% of the foaming agent, preferably no more than 2 wt% and optimally 0.1-1 wt%. The mixture is processed such that the coating material is particulate, the particles (31) containing both the metal and also the foaming agent. Independent claims are included for the following: (A) the corresponding coating material; (B) the functional layer so manufactured; (C) and the substrate with the functional layer.

Description

The invention relates to a method for producing a functional layer on a substrate, which is formed as a metal foam layer. Furthermore, the invention relates to a coating material for carrying out such a method, and to a method for producing the coating material. In addition, the invention relates to the use of the method for producing a functional layer and to such a functional layer.

It is known to produce moldings of metal foam and to use metal foam for filling metal profiles. For this purpose, typically commercially available metallic powder is mixed with a small amount of a blowing agent, for example a metal hydride. This mixture is compacted by known processes, e.g. Example by means of hot-extrusion, co-extrusion or heisisostatic pressing (HIP). This compacting process creates a dense body (precursor) of a starting material, which is usually malleable or workable. By supplying heat, this body is foamed and develops into a highly porous metal foam body. For this foaming the body is treated from the starting material in a shape corresponding to the desired shape with heat. In this case, the metal is liquid or at least plastic and the blowing agent releases gas (in metal hydrides, this is hydrogen), which penetrates in the form of bubbles in the liquid metal and this foams. This technology is for example in the US-A-5,151,246 described.

A known and commercially available product is aluminum foam, in which aluminum powder or an aluminum alloy serves as starting material. With aluminum foam, densities in the range of 0.5-1.0 g / cm ³ can typically be achieved, which corresponds to a porosity of up to 85%.

In addition to the enormous weight reduction that can be achieved with metal foam bodies or metal foam composites, metal foam also has other positive properties such as efficient energy absorption, especially under mechanical stress, high specific stiffness, good processability, good sound insulation properties, just to name a few ,

Today, the use of metal foam is limited to the filling of cavities - for example in metal carriers - or to the production of moldings by foaming the metal in a suitably designed form.

Starting from this prior art, it is an object of the invention to open up new fields of application for metal foam. In particular, a method for the production of metal foam is proposed, with the new applications of metal foam can be realized. Furthermore, a starting material for this purpose and a process for its preparation should be proposed. Furthermore, uses of the method or the starting material to be proposed.

The objects of the invention solving this object are characterized by the independent claims of the respective category.

According to the invention, therefore, a method is proposed for producing a functional layer on a substrate, in which, in a first step, a foamable coating material comprising a metal powder and a blowing agent is applied in the form of a layer to the substrate, and in a second step, the layer is foamed by heat input, so that the layer is converted into a metal foam layer.

The basic idea of the invention is therefore to use a foamable coating material as the starting material, to deposit it as a layer on a substrate and to foam this layer so as to produce a metal foam layer on the substrate.

This process opens up completely new applications for metal foam, because now foaming no longer requires the presence of a mold or cavity. The metal foam can be generated as a layer on a substrate.

In principle, any method known per se for producing layers on a substrate is suitable for the first step of the method according to the invention, for example spraying methods, thermal spraying methods, electrophoretic deposition, spray painting, screen printing or other printing methods, rolling, slurry methods, brushing, etc.

In a preferred process control, in the first step, the layer is applied to the substrate by means of a thermal spraying process, in particular by means of cold gas spraying. Here are two variants possible. On the one hand, the thermal spraying process can be carried out in such a way, in particular by means of cold spraying, that the coating material does not melt during the spraying process, so that the material is first deposited as a layer on the substrate and then foamed by heat input.

On the other hand, it is also possible to carry out the first and the second step of the method at least partially simultaneously. For this purpose, for example, the thermal spraying process can be carried out so that the particles of the coating material are already melted or plasticized on their flight to the substrate and foamed by the blowing agent. Of course, mixed forms of these two variants are possible.

Another preferred method procedure is when, in the first step, the layer is applied to the substrate by means of electrophoretic deposition. The coating material can be electrophoretically deposited in the form of a slurry or a slip by means of methods known per se.

For practical reasons, it is preferred if in the second step the heat input is carried out by means of a heating furnace or by means of electromagnetic radiation, in particular by means of laser irradiation, or by means of electromagnetic induction.

A preferred embodiment is that the coating material is a high nitrogen steel, with at most 4 weight percent nitrogen, preferably with 1 to 3 weight percent nitrogen, the nitrogen being at least partially released and foaming the metal. For this purpose, the layer is preferably applied by means of thermal spraying. The steel is thermally sprayed in powder form, releasing part of the nitrogen and causing the particles to "blow up". This embodiment is also possible with other high nitrogen coating materials.

• Bereitstellen eines Metalls in Form eines Pulvers, das eine vorgebbare Viskosität im geschmolzenen Zustand hat,
• Mischen des metallischen Pulvers mit einem Treibmittel, welches ein Gas zum Aufschäumen des Metalls freisetzen kann, wobei der Anteil des Treibmittel höchstens 5 Gewichtsprozent, vorzugsweise höchstens 2 Gewichtsprozent und speziell 0.1 bis 1 Gewichtsprozent beträgt,
• Verarbeiten der Mischung aus dem metallischen Pulver und dem Treibmittel zu dem Beschichtungsmaterial, derart dass das Beschichtungsmaterial ein Pulver ist mit Partikeln, wobei die einzelnen Partikel sowohl das Metall als auch das Treibmittel enthalten.

The invention further proposes a method for producing a coating material for carrying out the method according to the invention, comprising the following steps:

• Providing a metal in the form of a powder which has a predetermined viscosity in the molten state,
• Mixing the metallic powder with a blowing agent capable of releasing a gas to foam the metal, the amount of the blowing agent being at most 5 percent by weight, preferably at most 2 percent by weight and especially 0.1 to 1 percent by weight,
• Processing the mixture of the metallic powder and the blowing agent into the coating material such that the coating material is a powder with particles, the individual particles containing both the metal and the blowing agent.

This coating material, which is suitable for both thermal spraying and electrophoretic deposition, has the property that the individual particles contain both the metal and the blowing agent. It is therefore not a purely mechanical mixture of a metal powder with a propellant powder, but in the individual particles, the metal is "inseparably" connected to the propellant.

The invention further proposes a coating material for carrying out the method according to the invention, which is a powder with particles, wherein the individual particles contain both a foamable metal and a blowing agent which can release a gas for foaming the metal.

According to a preferred variant, the particles have a metallic core, which is coated with the blowing agent (cladded).

According to another preferred variant, the propellant is in each case dispersed in the particles, so that the particles each have a metallic matrix in which the propellant is incorporated. Due to this very even distribution of the blowing agent in the metallic phase, a very efficient foaming can be achieved.

Furthermore, a functional layer is proposed by the invention, prepared according to the inventive method or with a coating material according to the invention. Such functional layers can have different functions, e.g. As densities, stiffening, thermal insulation, sound insulation, connection of parts, etc.

The invention also proposes a substrate with such a functional layer. This may be, for example, a turbine blade to which a functional layer according to the invention is applied as a squish layer or enema layer.

The process according to the invention and the coating material according to the invention can be used in particular for Production of rubbing layers, running-in layers, seals, bearings, joining or filling material.

Further advantageous measures and preferred embodiments of the invention will become apparent from the dependent claims.

Fig. 1

eine schematische Darstellung eines Ausführungsbeispiels des erfindungsgemässen Verfahrens,

Fig. 2

eine schematische Darstellung eines Partikels eines ersten Ausführungsbeispiels des erfindungsgemässen Beschichtungsmaterials,

Fig. 3

eine schematische Darstellung eines Partikels eines zweiten Ausführungsbeispiels des erfindungsgemässen Beschichtungsmaterials, und

Fig. 4

eine schematische Darstellung eines Partikels eines dritten Ausführungsbeispiels des erfindungsgemässen Beschichtungsmaterials.

In the following the invention will be explained in more detail by means of embodiments and with reference to the drawing. In the schematic drawing show partly in section:

Fig. 1

a schematic representation of an embodiment of the inventive method,

Fig. 2

a schematic representation of a particle of a first embodiment of the inventive coating material,

Fig. 3

a schematic representation of a particle of a second embodiment of the inventive coating material, and

Fig. 4

a schematic representation of a particle of a third embodiment of the inventive coating material.

Fig. 1 1 is a schematic representation of a first exemplary embodiment of the method according to the invention for producing a functional layer 1 on a substrate 2, which is preferably a metallic substrate 2.

The function of the functional layer 1 can be, for example: increase in wear, abrasion, erosion resistance, sealing, connection of parts or materials, sound insulation, thermal protection, change in electrical or thermal conductivity, generation of squint or enema layers, etc.

The method according to the invention comprises two steps 100, 200. In the first step 100, a foamable coating material 3, which comprises a metal powder with a blowing agent, is applied to the substrate 2 in the form of a layer 1 '. Possible methods for producing the coating material 3, which in this embodiment is in powder form with particles 31, will be discussed further below.

In the second step, the layer 1 'by heat input, the in Fig. 1 symbolically represented by the arrows 4, foamed, so that the layer 1 'in the functional layer 1, which is a metal foam layer, is converted.

At the in Fig. 1 illustrated embodiment, the application of the layer 1 'takes place in the first step 100 by means of a thermal spraying process.

Thermal spraying processes are, for example, all forms of plasma spraying, flame spraying, HVOF processes. Furthermore, also such injection processes are known in which the process gas compared to the classic plasma spraying is "cold", for example at most a few hundred Kelvin, so that the particles are not melted in the gas stream and adhere to the substrate due to their kinetic energy. These processes, referred to in the literature as cold gas spraying or kinetic gas spraying, and hybrid processes (plasma cold gas spraying) are also to be encompassed by the term "thermal spraying" within the scope of this application, or by the term "thermal spraying".

At the in Fig. 1 The process illustrated is a plasma spraying process or a cold gas spraying process or a hybrid plasma cold gas injection process,

A spray device 5 is provided with which a process jet 6 can be generated, with which the substrate 2 is coated. In the case of plasma spraying, the spray device 5 comprises a plasma torch, not shown, in the case of kinetic spraying a cold gas spraying device, not shown,

In a manner known per se, the process jet 6 is generated with the spraying device 3 from the coating material M, a process gas or a process gas mixture G and optionally electrical energy E. The feed of these components E, G and coating material 3 is in Fig. 1 symbolized by the arrows 7, 8, 9 The produced process jet 6 exits through a nozzle 10 and transports the coating material 3 in the form of the particles 31 dispersed in the process jet to the substrate 2 in order to build up the layer 1 'there.

In the case of plasma spraying, the electrical energy E serves to generate the plasma. In the case of cold gas injection, the electrical energy E is usually used to heat the process gas G. However, in the typical cold gas injection process, the temperature of the process gas G is significantly lower than in the plasma spraying process and is usually at most a few hundred and up to 1000 ° C.

The coating material 3 comprises both a metal powder and a blowing agent. The metal powder and the blowing agent may be in the form of a mixture. For example, both the metal and the blowing agent may be in powder form. The coating material 3 may then be a mechanical mixture of the metal powder and the propellant. In the first step 100, a compacted layer of metal powder and propellant powder is then generated on the substrate 2. But it is also possible that the coating material is a metal powder with a blowing agent incorporated therein.

In the embodiment described here, as will be explained later, the particles 31 contain both the metal and the propellant. As propellants, for example, metal hydrides such as lithium hydride or titanium hydride are used. These have the property that they decompose above a material-specific decomposition temperature in the metal and gaseous hydrogen. Of course, other blowing agents such as metal nitrides or carbonates such as sodium carbonate (NaHCO ₃ ), sodium bicarbonate, potassium carbonate, calcium carbonate or hydrates such as aluminum hydroxide or high nitrogen-containing compounds, for example, by rapid solidification a supersaturated melt can be generated. Essential for the blowing agent is that by increasing the temperature of a gas is released, which can foam the metal.

The thermal injection process carried out in this exemplary embodiment as the first step 100 is carried out in such a way that the blowing agent releases substantially no gas during this process. The propellant is not heated above its decomposition temperature. Therefore, for the first step 100 in particular the cold gas spraying is particularly suitable, because in this the heat input into the particles during the injection process is significantly lower. It is no problem for a person skilled in the art to adjust the process parameters in the injection process in such a way that substantially no gas is released from the propellant during the spraying.

By this measure, the layer 1 'is deposited on the substrate 2 in a non-foamed state.

The choice of suitable blowing agent depends on the metal or composition of the metallic component of the coating material. The blowing agent is chosen so that its decomposition temperature or the temperature above which the gas is liberated for foaming, is in the range of the melting temperature of the metallic component of the coating material 3.

After the layer 1 'has been applied to the substrate 2 in the first step 100, the heat input 4 for foaming the layer 1' takes place in the second step 200. The heat input 4 can be done in various ways. The substrate 2 with the layer 1 'can be applied, for example, in a heating furnace with heat, or the layer 1' is acted upon by electromagnetic radiation, preferably by means of laser radiation. Furthermore, the heat input 4 by means of electromagnetic induction or by means of plasma treatment is possible.

By the heat input 4, the metal in the coating material 3 or in the layer 1 'is heated above its melting temperature and melts. The propellant decomposes, causing the gas to foam the now molten metal of the layer 1 'is released. As a result, the layer 1 'is converted into the formed as a metal foam layer functional layer 1, which in the lowermost part of Fig. 1 is shown.

Alternatively, an embodiment of the inventive method is possible in which the first step 100 and the second step 200 are at least partially performed simultaneously or simultaneously. In this case, the process parameters for the thermal spraying process, which is here preferably a plasma spraying, are carried out so that the particles 31 are already plasticized or melted in the process jet 6 and the blowing agent releases the gas for foaming the metallic component. Consequently, the particles 31 are already at least partially foamed or "inflated" in the process jet 6 on their way to the substrate 2 and then form the functional metal foam layer 1 on the substrate 2. The heat input 4 thus follows through the process beam 6, for example through the Energy of the plasma or the process gas.

Of course, these two embodiments can also be combined, that is, the thermal spraying process is performed so that it comes to an at least partial foaming of the particles 31 in the process beam 6 and then takes place an additional heat input 4 to the layer 2 located on the substrate to to complete the foaming.

In a further preferred embodiment of the method according to the invention, in the first step the layer 1 'is produced on the substrate 2 by means of electrophoretic deposition. For this purpose, the powdery coating material is processed with water or another liquid to a slurry or a slurry. With this takes place the electrophoretic deposition of the layer 1 'on the substrate 2, which is connected during the electrophoretic deposition as one of the two electrodes (anode or cathode). The second step, namely the foaming of the layer 1 'to the metal foam layer 1 takes place in a similar manner as already explained.

Of course, in variants, this embodiment of the slip instead of by electrophoretic deposition by other methods known per se in the form of a layer are applied to the substrate, for example by means of spray painting, by applying - for example with a brush. In principle, all processes known per se for applying a layer to a substrate are suitable for the first step of the process according to the invention, including printing processes such as screen printing or roll-coating. Preferably, the layer 1 'is applied as a uniform layer.

The invention further relates to a process for producing a coating material which is suitable for carrying out the process according to the invention, such as such a coating material, which is explained in more detail below.

The coating material 3 is a powder comprising a metal powder having a blowing agent incorporated therein for releasing a gas for foaming the metallic component. The powdered coating material comprises particles 31, each containing both the metal 32 (see, eg Fig. 2 ) as well as the propellant 33. This means that at least a substantial proportion of the particles 31 of the coating material, for example at least 75% of the particles of the coating material 3, each contain both the metal 32 and the blowing agent 33. Thus, the two components metal 32 and blowing agent 33 each form an "inseparable" composition in the particles 31, in the sense that the individual particle 31 combines both components 32, 33 in itself.

Depending on the manufacturing process, different variants for the design of the particles are possible. In the Fig. 2-4 three different embodiments for each one particle 31 of the coating material 3 are shown schematically.

At the in Fig. 2 In the first embodiment shown, the particle comprises two substantially separate regions, one of which is formed by the metal 32 and the other by the blowing agent 33.

In the second embodiment according to Fig. 3 the particle 31 has a metallic core 32 which is coated with the blowing agent 33 (cladded particle)

In the third embodiment, which is in Fig. 4 is shown schematically, the propellant 33 forms a disperse phase, which is distributed as uniformly as possible over the metallic phase 32. Here, the metal 32 forms a metallic matrix in which the blowing agent 33 is embedded. This third embodiment is particularly preferred because it ensures a very uniform distribution of the propellant 33, which has an advantageous effect on the foaming process.

For the preparation of the coating material 3, a metal powder and a suitable blowing agent is first selected. Examples of suitable blowing agents, such as a metal hydride powder, have been mentioned earlier. The metal powder may be either an elemental metal such as aluminum or an alloy or a mixture of several metals.

First, the metal is provided in the form of a powder having a predetermined viscosity in the molten state. On the one hand, the metal in the liquid state must not be so low in viscosity that the gas released by the blowing agent leaves the metal without exerting an intumescent effect. On the other hand, the metal must not be too viscous in the liquid state, because otherwise the blowing agent can not foam the liquid metal. In order to adjust the viscosity of the metal in the molten state to a value suitable for foaming, it is known to add a ceramic powder to the metal in the liquid phase to thicken the metal. When the viscosity of the liquid metal has the correct value, the metal is processed into a powder in a manner known per se.

In the next process step, the metallic powder is mixed with the blowing agent, which is preferably also in powder form. For this purpose, a suitable for the respective metal powder blowing agent is first selected. An essential criterion here is that the Decay temperature of the blowing agent, ie the temperature at which the blowing agent releases the gas for foaming, is in the range of the melting temperature of the metallic powder.

The amount of blowing agent is determined according to the desired porosity of the metal foam layer to be produced. However, the proportion of blowing agent is at most five percent by weight (wt.%). In practice, it has proven particularly useful if the proportion of blowing agent is at most 2% by weight and in particular 0.1-1% by weight.

The blowing agent is intimately mixed with the metal powder. This mixture of the blowing agent and the metallic powder is then processed into the coating material 3, which is present as a powder with particles, the individual particles containing both the metal and the blowing agent (see Fig. 2-4 ). This processing can be carried out by methods known per se, for example in an atomizer or by spray drying and granulation. In this case, it may be advantageous to first briefly melt the powder mixture.

This in Fig. 3 illustrated second embodiment in which the metallic core 32 is coated with the blowing agent 33 is prepared for example by the metal powder to be coated is introduced into a suspension of solvent, fine blowing agent powder and an adhesion promoter, preferably on an organic basis. When the solvent is removed with constant stirring, the metal powder is coated with a thin layer of the blowing agent.

Subsequently, a post-processing of the powdered coating material can take place, for example in order to round or round the individual particles.

The particle size of the particles 31 is for example 50 microns. The necessary or suitable particle size of the particles 31 depends on the coating method used or the coating system used. In thermal spraying, the particle sizes are typically between 25 μm +/- 5 μm and 100 μm +/- 50 μm. In the Electrophoretic deposition requires significantly finer particles in the range of 5 μm and below to prevent the particles from settling too quickly.

Another variant for the blowing agent is that the coating material used is a highly nitrogen-containing compound, for example a steel containing a high nitrogen content, which means a steel which contains at most 4% by weight of nitrogen, preferably 1-3% by weight of nitrogen. Such high nitrogen-containing compounds generally have the property of releasing the nitrogen back into gaseous form upon heating. This discharged at heat input 4 nitrogen can then serve as a gas for foaming.

Since the solubility of nitrogen in steels above about 1000 ° C increases significantly, such a coating material can be prepared in which the steel is supersaturated at over 1000 ° C with nitrogen. Subsequently, the melt is very quickly solidified.

If such a high nitrogen-containing coating material is then applied as layer 1 ', the layer can be foamed by heat input 4 with the nitrogen present in the coating material.

Metal foam layers made of high nitrogen steel have very good mechanical properties and provide high corrosion protection.

The functional layer produced according to the invention, which is designed as a metal foam layer, can be used in a variety of ways. In the following, only a few uses of the process according to the invention for producing a functional layer or of the coating material according to the invention are to be mentioned: Preparation of anticorrosive layers, hard coatings, abradable layers and enema layers, eg. As components of turbines such as turbine blades or segments with multiple turbine blades, production of seals, bearings, plain bearings, connecting material

Claims (12)

Method for producing a functional layer on a substrate, in which, in a first step (100), a foamable coating material (3) comprising a metal powder and a blowing agent is applied to the substrate (2) in the form of a layer (1 ') , and in a second step (200), the layer (1 ') is foamed by heat input (4), so that the layer is converted into a metal foam layer (1). The method of claim 1, wherein in the first step (100) the layer (1 ') by means of a thermal spraying process, in particular by means of cold gas spraying is applied to the substrate (2). The method of claim 1, wherein in the first step (100), the layer (1 ') is applied by electrophoretic deposition on the substrate (2). Method according to one of the preceding claims, wherein in the second step (200) the heat input (4) by means of a heating furnace or by means of electromagnetic radiation, in particular by means of laser irradiation, or by means of electromagnetic induction is performed. A method according to any one of the preceding claims wherein the coating material (3) is a high nitrogen steel having at most 4 weight percent nitrogen, preferably from 1 to 3 weight percent nitrogen, the nitrogen being at least partially released and foaming the metal. A process for producing a coating material for carrying out a process according to any one of claims 1-5 with the following steps - Providing a metal in the form of a powder, the one has predetermined viscosity in the molten state, Mixing the metallic powder with a blowing agent which can release a gas for foaming the metal, the proportion of the blowing agent being at most 5% by weight, preferably at most 2% by weight and especially 0.1 to 1% by weight, Processing the mixture of the metallic powder and the blowing agent into the coating material, such that the coating material (3) is a powder with particles (31), the individual particles (31) containing both the metal (32) and the blowing agent (33 ) contain. A coating material for carrying out a method according to any one of claims 1-5, which is a powder with particles (31), the individual particles containing both a foamable metal (32) and a blowing agent (33) containing a gas for foaming the metal can release. A coating material according to claim 7, wherein the particles (31) comprise a metallic core (32) coated with the blowing agent (33). A coating material according to any one of claims 7-8, wherein the blowing agent (33) is dispersed in each of the particles (31) such that the particles (31) each comprise a metallic matrix (32) in which the blowing agent (33) is incorporated. Functional layer produced according to a method according to one of claims 1-5 or with a coating material (3) according to one of claims 7-9 Substrate with a functional layer (1) according to claim 10 Use of a method according to any one of claims 1-5 or a coating material according to any one of claims 7-9 to Production of rubbing layers, running-in layers, seals. Storing, connecting or filling material.

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