WO2014191155A1

WO2014191155A1 - Method for producing a metal foam and method for producing particles suitable for said method

Info

Publication number: WO2014191155A1
Application number: PCT/EP2014/059000
Authority: WO
Inventors: Jens Dahl Jensen; Ralph Reiche; Daniel Reznik
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-05-31
Filing date: 2014-05-02
Publication date: 2014-12-04
Also published as: DE102013210198A1; CA2913833A1; EP2981380A1; US20160090653A1

Abstract

The invention relates to a method for producing a metal foam, in which metal-containing particles (22) and blowing-agent-containing particles (23) are deposited by cold spraying. According to the invention, a layer (17) formed in this manner is formed from metallic particles (22) and particles (23) containing blowing agent (24), wherein the blowing agent forms the core of coated particles (23). The shell (25) of said particles is likewise metallic, for which reason it is easier to deposit said particles together with the metallic particles (22). Therefore, a higher concentration of blowing agent can advantageously be produced in the layer (17). Greater possibilities are advantageously produced thereby to provide the porous layers with required pore profiles. The invention further relates to a method for producing the particles having a core (24) of blowing agent and a shell (25) of metal.

Description

description

Method for producing a metal foam and method for producing particles suitable for the aforesaid method

The invention relates to a method for producing a metal foam, wherein the metal-containing particles are deposited together with a solid propellant-containing particles by cold gas injection as a layer on a substrate. Thereafter, the blowing agent is activated, wherein the pores of the metal foam form in the layer. Such Akti ^¬ vation can be done for example by means of a heat treatment. The layer is heated to the point that the

Propellant from the solid into a gaseous state passes. The associated pressure increase leads to the formation of pores in the metallic matrix. The heat treatment is carried out in temperature ranges in which the metallic matrix is softened so far that the pores can form.

Moreover, the invention relates to a method for producing coated particles. The production of metal foams by cold gas spraying is known from US Pat. No. 6,464,933 B1 and US Pat. No. 7,402,277 B2. In this case, particles are processed from the metal, which is to form the metallic matrix of the metal foam. The ^¬ sem material are admixed particles of the blowing agent, which are deposited in the metallic matrix. However, the rate of deposition of the blowing agent is as ^¬ by limited such that it is suitable for deposition by cold gas spraying regards its characteristics in principle limited. It is generally known that brittle materials, as is the case with the materials of the blowing ^agent , can be deposited only to such an extent in the metallic matrix formed by the much more ductile metallic particles, such as Forming the particles on impact allows incorporation of the brittle particles. Therefore, the pore density is limited in the deposition of the particles of the blowing agent. The object of the invention is therefore to provide a method for producing a metal foam by cold gas spraying and a method for producing suitable particles for the method of cold gas spraying, with which metal foams are produced, their pore density and

Pore is variable over the largest possible range.

This object is achieved according to the invention it ^¬ with the above-mentioned method characterized in that the drive means comprise ^¬ particle gemantelte particles having a core of the

Blowing agent and a metallic shell can be used.

These can then be deposited together with the metal-containing particles, wherein the metal-containing particles contain in particular exclusively metal. The advantage of a mantle of the propellant with a metallic material is that these coated particles behave similar to the particles of a metal during processing. On opening of the jacketed particles the shells provide a reserve of ductility in terms of Ver ^¬ holding the jacketed particles available, so that the deformation of the shells in the forming layer ensures an improved installation of the particles. This has the advantage that the concentration range of the particles containing the blowing agent in the forming layer can be varied to a greater extent. It depends primarily on the thickness of the casings, the process parameters and the desired layer result, how high the proportion of the propellant-containing particles in the spray powder should be. Here, concentrations of the particles containing the propellant can be adjusted between 0 and 100% (the percentage indication represents the numerical proportion of the particles). In this respect, it is also possible to process 100% of the particles containing the blowing agent, if the shell of the metal is sufficiently thick. So in the case deposited only one type of particles, which have both the property of the propellant-containing particles as well as the property of the metal-containing particles. Cold spraying is a method known per se, are preferably accelerated at the foreseen for the coating particles by means of a convergent-divergent nozzle onto Überschallge ^¬ speed, so that they stick to the surface to be coated due to their impressed kinetic energy. Here, the kinetic energy of the particles Ener ^¬ is used, which leads to a plastic deformation thereof, whereby the coating particles are fused only on its surface upon impingement. Therefore, this method is referred to as cold gas spraying in comparison to other thermal spraying methods, because it is carried out at comparatively low temperatures at which the coating particles remain substantially fixed. Preferably, for cold gas spraying, which is also called kinetic spraying, using a cold gas spraying installation having a gas heating means to overheat He ^¬ a gas. To the gas heater a stagnation chamber is connected, which is connected on the output side with the convergent-divergent nozzle, preferably a Laval nozzle. Convergent-divergent nozzles have a merging section and a flared section connected by a nozzle throat. On the output side, the convergent-divergent nozzle generates a powder jet in the form of a gas stream with particles in it at high speed, preferably at supersonic speed.

According to an advantageous embodiment of the invention, it is provided that aluminum, copper, nickel, iron, steel or silver are used as materials of the shell. These materials are advantageously very ductile, which is why

Choice of these materials, the proportion of the propellant enthal ^¬ border particles can be advantageously selected very high. With less ductile materials can be inventively increase the range of variation of the possible proportion of the propellant-containing particles also, in which case a range of variation between 0 and 100% is not achieved. With the available ductile materials, however, have diverse constructive Aufga ^¬ ben can be managed. For example, aluminum can be used to produce metal foams for lightweight construction. This metal has a low density anyway, but can be used by forming pores for the production of even lighter components. Copper and silver have beneficial ^¬ way a high thermal and electrical conductivity. Are the ^¬ se materials may thus for example be used as a heat exchanger material, the pores in the formation of the inner channel structures for the passage of a fluidically which is to be heated or cooled the suitable. Iron and steel are common construction materials, which are also inexpensive. Hereby ver ^¬ different design components can be produced, which can be improved by a Schierstoff in the formed pore systems, for example, the lubricating properties.

According to another embodiment of the invention, it is provided that the material of the shell is equal to the material of the exclusively metal-containing particles. As a result, a metal foam is generated, which forms a metallic matrix of only one metallic material. The material of the shell is built into this metallic matrix, so to speak. However, this is not necessarily required. For example, the material of the sheaths could also be a catalytically active material which is deposited into the pore surfaces while the metal foam is forming. Then the exclusively metal-containing particles would only be the support framework for such a catalytic structure. This structure could be exploited catalytically in the formation of an open metal foam (to the production possibilities of open and closed metal foams in the following even more). Yet another embodiment of the invention provides that the material of the core is a metal hydride, in particular magnesium hydride or titanium hydride, or a carbonate, in particular calcium carbonate or magnesium carbonate. In the ^¬ sen propellants is customary propellants for the production of metal foams. These provide a reasonable temperature range during their activation, so that depending on the softening temperatures of the metallic matrix, a suitable blowing agent can be selected. This is with the help of general expertise and z. B. with the involvement of the above-mentioned US 6,464,933 Bl and US 7,402,277 B2 possible.

Furthermore, it is advantageous if the mixing ratio between the particles containing the blowing agent and exclusively metal-containing particles is varied during the coating. Here, different tasks of the trainees metal foam can take into account the ^¬. It is possible to produce gradient layers with variable density of the pores. It is also possible that the density of the pores by properly adjusting the blend ratio in the ^¬ adjacent to the substrate interface layer, ie the layer portion, which lies directly on the substrate, and / or in the obeflächennahen boundary layer, so

Layer portion, which is involved in the formation of the surface, only the metal-containing particles are processed. This has the advantage that a pore-free surface of the layer can be generated and also a po ^¬ renarme boundary layer can be formed to the substrate. ^Hereby , the surface properties of the layer can be influenced in the desired manner and it is possible to maximize the adhesion between the layer and the substrate. It is also advantageously possible for the density of the pores in the boundary layer adjacent to the substrate to be maximized by processing exclusively the particles containing the blowing agent. This causes in the training of the Metal foam the adhesion of the layer on the substrate is largely lifted ^¬ . After the metal foam has been produced, therefore, the layer can be detached from the substrate without problems. In this case, the substrate provides its surface only as a basis for producing a discrete component in the form of the layer. The layer becomes a self-supporting, independent component. This may be a heat exchanger plate in ^¬ play, whose mass can be optimized before ^¬ part adhesive by peeling the substrate after manufacture of the metal tallschaums.

It is also advantageous if the metal foam is generated by following the coating on completion of which heat ^¬ treatment of the layer. In other words, the first layer is completed and then performed a Wärmebe ^¬ action, in which the metal foam. The energy input of the cold gas spraying is therefore too low that it is insufficient to activate the blowing agent during the deposition of the layer. This method is preferred for closed metal foams herzustel ^¬ len. Even with a large proportion of propellant-containing particles walls will form between the individual pores due to the deformation of the envelopes. Another possibility is that the Energieein ^¬ contract during cold gas spraying and / or an energy input in the substrate are chosen so high that the particles containing the blowing agent are heated upon impinging on the substrate to a temperature above the reaction temperature of the blowing means. The energy input during the cold gas fuel ^¬ zen can be increased for example by a pre-heating of the propellant gas. This is then transferred to the particles to varying degrees by a different residence time of the particles in the stagnation chamber, which is upstream of the cold spray nozzle. If the heat input into the particles containing the blowing agent and into the particles consisting solely of metal should be of different heights, it is possible to control the feed points of these particles. in the stagnation chamber at different distances to the cold spray nozzle. Two different feed points for the particles containing the blowing agent as well as the exclusively metallic particles are in any case advantageous if the concentration of the particles containing the blowing agent is to be varied. For this purpose, namely, an independent feed of both types of particles of advantage, since not powder with different mixing ratios ^¬ must be gefangen sen.

The energy input into the substrate can be done, for example, by preheating the same. Another possibility is to achieve local heating of the substrate (and of the substrate provided with the layer under construction) by irradiating the point of impact of the cold gas jet with a laser beam. In any case, the additional energy input means that the blowing agent is already activated when the particles containing the blowing agent strike the substrate. The metal pores form as it were in situ and increase at the impact of these particles, the porosity of the substrate, so the formation of pores. In this case, since the pore formation occurs at the time of severe plastic deformation of the particles, the shells of the particles containing the blowing agent are destroyed during the reaction. In this way, open-cell metal foams can be produced if the concentration of particles containing the blowing agent is chosen to be sufficiently high so that sufficient particles containing the blowing agent are deposited directly adjacent in the constituent layer and in this way ensures a connection of the forming pores with each other is.

Furthermore, the object is achieved by a procedural ^¬ ren for the preparation of the jacketed particles, which consists of cores are composed of a blowing agent, created by these cores are surrounded by sleeves made of a metal. Advantageously, the coating of the cores with the Envelope be carried out by a current-free electrochemical process. These methods are well known.

Further details of the invention are described below with reference to the drawing. Identical or corresponding drawing elements are each provided with the same Bezugszei ^¬ chen and are only explained several times as far as differences arise between the individual figures. Show it

1 shows an embodiment of erfindungsge ^¬ MAESSEN method schematically, the

Figures 2 to 9 different embodiments of the porous layers before and after each

Activation of the propellant and

10 shows an embodiment of the erfindungsge ^¬ MAESSEN method for producing the coated particles.

According to Figure 1, a substrate 11 is coated by means of a cold spray system ^¬ 12th Only a stagnation chamber 13 and connected to the stagnation chamber convergent-divergent nozzle of the cold spray system are exempla ^¬ driven Darge 14 provides ^¬. The nozzle 14 generates a cold gas jet 15, with the particles 16 are deposited on the substrate 11, whereby the layer 17 is formed. Meanwhile, the substrate 11 is preheated by a heater 18. In addition, a laser beam is directed at the impact site of the cold gas jet ^¬ 15 19 by means of a laser 21st Also, the carrier gas can be preheated in the Stag ^¬ tion chamber 13 by means of a heater 20.

According to Figure 2, the layer 17 is shown in section. It can be seen that on the substrate 11 particles 22, which are ^¬ finally made of a metal, as well as jacketed particles 23, which have a core 24 of a blowing agent and a shell of the metal, are deposited. After this Cold gas spraying of the layer, the coated substrate is subjected to a heat treatment in which the propellant of the cores 24 is activated. The layer result after the heat ^¬ treatment is shown in Figure 3. It can be seen that pores 26 have formed in the metallic matrix of the layer 17. This creates a metal foam.

In the layer 17 according to FIG. 2, the particles 23 containing the blowing agent are uniform over the entire length

Layer thickness distributed. As can be seen from FIG. 3, pores are also formed in the edge region of the pores

Layer. This means that pores can form an interface to the upper surface of the substrate ^¬ 11, as can be seen in the pore 26a. It is also possible that the pores are open to the surface 27 of the layer, as can be seen in the pore 26b.

According to Figure 4, the layer 17 in three stages abgeschie ^¬ the. In a stage I, only metallic particles 22 are deposited. In a stage II, a mixture of the propellant-containing particles 23 and metallic particles 22 is deposited. In a stage III again only metallic particles 22 are deposited. As can be seen from FIG. 5, a layer 17 with pores 26, which are formed only in the interior of the layer, is formed in this way. The surface 27 and an interface 28 to the substrate 11 are pore-free because of the deposition phases I and III. The adhesion of the layer 17 to the substrate 11 is therefore not affected by the pores 26, just as the surface quality of the surface 27 of the layer 17.

In phase II according to FIG. 4, propellant gas-containing particles 23 were deposited in such a low concentration that the pores 26 forming are self-contained, ie that these pores are completely separated from the matrix material Layer 17 are surrounded. This creates a

closed-pore metal foam.

According to FIG. 6, the layer 17 is separated into two phases I, II, which correspond to the phases I, II according to FIG. However, so that the upper surface of the deposited ^¬ according to FIG 6 layer partially containing also by the propellant particles is dispensed to the phase III, 23 ausgebil is ^¬ det. In addition, the particles, the propellant-containing gas are larger than the metal particles 22. Considering now the layer result according to Figure 7 after Heat Treatment ^¬ lung, it is found that the particles of the propellant containing 23 effects due to their higher concentration and their size to that common pores have been formed. The cases 25 have been destroyed. Since the phase III was dispensed with in the deposition, the openings of the pores 26 are partially also in the surface 27, so that an open-pore metal foam is formed in the layer 17, wherein the channels are accessible from the surface 27. In these pores, for example, a liquid

Lubricant are introduced. Another possibility would be the introduction of catalytic particles (not shown). According to Figure 8, the layer 17 into four phases abgeschie ^¬. The concentration of the propellant gas-containing particles 23 is hatched over the layer thickness schematically Darge ^¬ represents. In phase I, only propellant-containing particles are separated (concentration = 100%). In a phase II exclusively metallic particles are separated from ^¬ (concentration of the propellant gas-containing particles = 0%). In a phase III, a gradient layer is Herge ^¬ is, by making the concentration of the blowing agent-containing particles 23 increased from 0 to 80% and then to-back down to 0%. In a phase IV again only metallic particles are deposited (concentration of the propellant-containing particles = 0%). The layer result after the heat treatment can be seen in FIG. The deposition of propellant-containing particles in phase I cause the layer 17 in the heat treatment from the substrate 11 detaches. It creates, so to speak, a single large pore between sight and

Substrate. The layer 17 thus represents an independent plate-shaped component after the heat treatment. This could for example be used as a heat exchanger plate. Phases II and IV lead to this plate-shaped component having a closed surface. The Endkonzentra ^¬ tion of 80% blowing agent-containing particles in the

Gradient layer deposited in phase III causes an open-pored channel system to be formed inside the layer 17, which more or less results in a continuous cavity and columnar

Structures 29 is supported. This channel system could be used for the passage of a fluid which is to exchange heat with another fluid beyond the surfaces 27 of the layer 17.

According to FIG. 10, by way of example, a particle 23 is produced in a bath 30 by electroless deposition of the casing 25 on the core 24. The electroless deposition of metals is known per se. For example, copper or nickel can be deposited electrolessly.

Claims

claims

1. A method for producing a metal foam, in which

- Metal-containing particles (22) together with a solid propellant-containing particles (23) by cold gas spraying as a layer (17) on a substrate (11) abge ^¬ separated and

- The propellant is activated, leaving the pores

(17) of the metal foam in the layer (17) form, d a d u r c h e c e n e c e n e,

in that the propellant-containing particle (23)

coated particles having a core (24) of the propellant and a metallic shell (25) are used.

2. The method according to claim 1,

characterized,

that as materials of the shell (25) aluminum, copper, nickel, iron, steel or silver are used.

3. The method according to claim 1 or 2,

characterized,

that the material of the sheath (25) is equal to the material of the finally metal-containing particles from ^¬ (22).

4. Method according to one of the preceding claims,

characterized,

that the material of the core (24), a metal hydride, magnesium hydride or insbeson ^¬ particular titanium hydride, or a carbonate, in particular calcium carbonate or magnesium carbonate.

5. The method according to any one of the preceding claims,

characterized,

in that the mixing ratio between the particles (23) containing the blowing agent and particles (22) containing only metal is varied during the coating.

6. The method according to claim 5,

characterized, a gradient layer +19 with variable density of the pores (26) is produced.

7. The method according to claim 6,

characterized,

the density of the pores (26) in the boundary layer adjacent to the substrate and / or in the near-surface boundary layer is lowered to zero, by processing exclusively the particles (22) containing exclusively metal there.

8. The method according to claim 5,

characterized,

in that the density of the pores (26) in the boundary layer adjacent to the substrate is maximized by processing exclusively the particles containing the blowing agent.

9. Method according to one of the preceding claims, characterized in that

the metal foam is produced by a heat treatment of the layer (17) following the coating after its completion.

10. The method according to any one of claims 1 to 8,

characterized,

that the energy input during cold gas spraying and / or an energy input in the substrate are chosen so high that the blowing agent-containing particles (23) onto the substrate when striking ^¬ fen (11) are heated to a temperature above the reaction temperature of the propellant.

11. Method for producing coated particles (23) d a d u r c h e c e n e c e n e,

that these are produced from cores (24) consisting of a propellant, by surrounding these cores (24) with casings (25) of a metal.

12. The method according to claim 11, characterized,

in that a current-free electrochemical process is used for coating the cores (24) with the sheath (25).