EP2261397A1 - Method of producing a metal matrix compound material - Google Patents

Abstract

The method for producing a metal matrix composite material, comprises a metal matrix having metal component, and a reinforcing component arranged in the metal matrix. One of the components is sprayed onto a substrate (5) by a thermal spraying process, where the reinforcing component consists of carbon in the form of nanotubes, nanofibers, graphenes, fullerence, flakes or diamond. The spraying process is cold gas spraying, flame spraying and/or plasma spraying. The substrate is a film, a substrate with non-wettable surface, workpiece to be coated, and/or a semi-finished product. The method for producing a metal matrix composite material, comprises a metal matrix having metal component, and a reinforcing component arranged in the metal matrix. One of the components is sprayed onto a substrate (5) by a thermal spraying process, where the reinforcing component consists of carbon in the form of nanotubes, nanofibers, graphenes, fullerence, flakes or diamond. The spraying process is cold gas spraying, flame spraying and/or plasma spraying. The substrate is a film, a substrate with non-wettable surface, workpiece to be coated, a semi-finished product and/or three-dimensional structure. The surface of the substrate and/or the metal-matrix composite material is processed. The metal component and/or reinforcing component are provided in particle form. A first component is mixed before the spraying with a further component. The reinforcing component is organic and/or ceramic reinforcing component. An independent claim is included for a metal matrix-composite material.

Description

The invention relates to a method for producing a metal matrix composite material having a metal matrix having at least one metal component and at least one reinforcing component arranged in the metal matrix, a corresponding material, in particular in the form of a coating, and the use of such a material.

The trend toward increasing miniaturization, the cost pressures associated with rising material costs, and the increasingly demanding requirements of applications in the electrical and electronic industries, as well as the manufacture of technical bearings, require new materials and coatings.

Metal matrix composites or metal matrix composites (MMC) have outstanding combinations of properties compared to exclusively ceramic or metallic materials. For this reason, there is a great deal of interest in using the MMC, originally developed for the aerospace and defense industries, for a number of applications.

The term MMC often refers exclusively to appropriately reinforced aluminum, in special cases also referred to as reinforced magnesium and copper materials. The metal component of the MMC is as elemental metal or in the form of an alloy. As reinforcement phase or component are usually particles (reinforcing particles) (diameter 0.01-150 microns), short fibers (diameter 1-6 microns, length 50-200 microns), continuous fibers (diameter 5-150 microns) or foams with of open porosity, which are usually made of ceramic material (SiC, Al ₂ O ₃ , B ₄ C, SiO ₂ ) or carbon in the form of fibers or graphite (see also and in the following: "Metal matrix composites: properties, Applications and Editing "by Dr. O. Beffort, 6th International IWF Colloquium, 18/19 April 2002, Egerkingen, Switzerland).

For the production of bulk MMC materials, three processes are known from the prior art, namely the stirring of ceramic particles into the molten metal, the melt infiltration and the powder metallurgy. For the production of MMC coatings, the prior art discloses the electrodeposition.

In corresponding stirring often the lack of wettability between molten metal and particles must be overcome and a reaction between the two phases are limited. The volume fraction of the particles is limited for viscosity reasons to a maximum of 30%.

During infiltration, the reinforcing component is processed into a porous preform into which the molten metal is subsequently infiltrated with or without pressure. In this case, fibers and foams with very high amplification volume fractions (up to about 80%) can be used as reinforcement in addition to particles become. A local reinforcement in areas of highest stress is possible. However, corresponding methods are expensive.

The powder metallurgy (PM) of MMC differs from commonly used PM processes only in that instead of a metal powder, a powder mixture of ceramic or Verstärkungskomponenten- and metal particles is used. The PM is only suitable for fine particles (particle size 0.5-20 μm). In addition, a subsequent formability of the MMC obtained by extruding, forging or rolling must be ensured, whereby the maximum volume content of the reinforcing particles is limited to about 40%.

In the case of the electrodeposition of dispersion layers, there is the problem of levitating the particles finely distributed in the electrolyte and at the same time depositing them with the matrix in order to obtain homogeneous layers. The simultaneous deposition of particles and matrix is in many cases impossible because of their different potentials.

Carbon nanotubes (CNT) have outstanding properties. These include, for example, their mechanical tensile strength of about 40 GPa and their stiffness of 1 TPa (20 or 5 times steel). Both CNTs with conductive and those with semiconducting properties exist. CNTs belong to the family of fullerenes and have a diameter of 1 nm to a few 100 nm. Their walls, like the fullerenes or, like the planes of graphite, consist only of carbon. In particular, a mixture of CNT with other components lets expect composite materials and coatings with significantly improved properties.

It is known to mix CNT with conventional plastic to improve its mechanical and electrical properties. Metal-based CNT composites, such as those in the DE 10 2007 001 412 A1 include a metal matrix such as Fe, Al, Ni, Cu, or their alloys, and carbon nanotubes as a reinforcing component in the matrix. Due to the large density differences between metals and CNT and the resulting strong demixing tendencies as well as the lack of wettability of the CNT with metal, a melt metallurgical application for the production of corresponding metal-CNT composite materials is problematic. The DE 10 2007 001 412 A1 therefore proposes to deposit on a substrate an electroplated composite coating by using a plating solution containing metal cations of a metal matrix to be deposited and carbon nanotubes. The composite coating then comprises the metallic matrix and carbon nanotubes disposed in the matrix, thereby improving the mechanical and tribological properties of the coating. However, galvanic application is difficult or impossible to achieve in many areas.

The invention has for its object to provide a method for producing a metal matrix composite material, in particular with CNT as a reinforcing component, which allows to distribute the components used in a technically simple manner as evenly as possible, wherein In particular, the reinforcing components should be as unchanged as possible in their physicochemical properties and contained in the metal matrix composite material to the highest possible percentage.

This object is achieved by a method for producing a metal matrix composite material and by such a metal matrix composite material, which can be used as such as a workpiece or as a coating of a workpiece or as a material for producing a workpiece, having the features of the independent claims. Preferred embodiments are given in the respective dependent claims.

The invention includes the technical teaching of injecting at least one of the components onto a substrate by means of a spraying process for producing a metal matrix composite material having a metal matrix having at least one metal component and at least one reinforcing component arranged in the metal matrix.

By appropriate spraying method metal powder, which were previously mixed, for example, with carbon components such as CNT or ceramic reinforcing components, are used. The proportion of metallic particles in the carrier gas can be, for example, in a range of 0.1 to 50%.

Spray processes, such as flame, plasma and cold gas spraying are known from the prior art for the production of coatings. In flame spraying, a powder, cord, rod or wire coating material is heated in a fuel gas flame and while supplying additional carrier gas, for example compressed air, injected at high speed onto a base material. In plasma spraying, powder is injected into a plasma jet, which is melted by the high plasma temperature. The plasma stream entrains the powder particles and throws them onto the workpiece to be coated.

When cold gas spraying, as for example in the EP 0 484 533 B1 is described, the spray particles are accelerated to high speeds in a comparatively cold carrier gas. The temperature of the carrier gas is a few hundred ° C and is below the melting temperature of the lowest-melting component sprayed. The coating is formed with the impact of the particles on the high kinetic energy metal tape or component, the particles which do not melt in the cold carrier gas forming a dense and adherent layer upon impact. The plastic deformation and the resulting local heat release thereby ensure a very good cohesion and adhesion of the sprayed layer on the workpiece. Owing to the relatively low temperatures and the possibility of using argon or other inert gases as the carrier gas, oxidation and / or phase conversions of the coating material during cold gas spraying can be avoided. The spray particles are added as a powder, usually with a particle size of 1 to 100 microns. The high kinetic energy obtained the spray particles in the relaxation of the carrier gas in a Laval nozzle.

In the present invention, at least one of the components is preferred by cold gas spraying, flame spraying, in particular high velocity flame spraying (HVOF), and / or plasma spraying. It is also contemplated, especially in cold gas spraying, to use a carrier gas whose temperature is at room temperature or below, whereby a thermal load of the sprayed components, in particular the reinforcing components, can be safely avoided. The temperature may range to, for example, 10% below the melting temperature of the lowest melting component. The carrier gas should simultaneously create an inert or even reducing atmosphere in order to prevent oxidation of the powder particles and thus not adversely affect the later layer or material properties such as electrical conductivity, among other things. In particular, a combination of two spraying methods can also be used. A use of two spray nozzles with a mixture of the corresponding components at the coating site is also possible.

As a result of the measures mentioned, significantly improved properties of the coatings and materials produced thereby can be achieved. The corresponding products have an increased wear resistance, a better sliding behavior and a higher friction corrosion resistance, wherein the friction coefficient can be reduced to about one tenth of the value of the respective pure metal. Furthermore, the conductivity and the hardness of the materials are increased.

The invention provides a particularly flexible and cost-effective method, since, for example, in the production of printed conductors, lead frames and lead frames no pre-fabrication steps such as rolling, punching or annealing are required by the intended spraying process.

The substrate used in the process according to the invention may be a film or a substrate which is not wettable by the powder jet, which makes it possible to separate spray-applied metal matrix composite materials from the substrate. In this way, a component or a pure material, for example in the form of a strip, can be obtained, which can then be further processed in a suitable manner.

However, tape materials and components such as electromechanical components, heatsinks, bearings, and bushings may also be adhesively coated which have improved properties through the metal matrix composite. For the purposes of this invention, a metal strip or an electromechanical component is preferably used as the workpiece, which preferably consists of ceramic, titanium, copper, aluminum and / or iron and alloys thereof. Semifinished products or 3D structures such as Molded Interconnection Devices (MID) can also be used for coating.

According to a particularly preferred embodiment, the method includes at least one surface processing step. Here, for example, on a metal strip or component made of a metallic material, an activation, a Haftungsvermittlungs- and / or a diffusion barrier layer are applied to which then the MMC are sprayed. If no adhesive coating is desired, but should, as As shown above, a pure metal matrix composite can be obtained, instead of an adhesion-promoting layer also a non-stick coating can be applied.

Corresponding MMC tapes or coatings can also be subsequently subjected to an additional treatment, such as leveling or a reflow / heat treatment, for the purpose of smoothing the surface. For forming, for example, a soft annealing step, for example at about 0.4 times the melting temperature of the matrix metal, can also be carried out subsequently. For compacting the material and / or for reducing the porosity at the surface, the material can be re-rolled, for example with a degree of deformation of 0.1 to 10%.

In corresponding methods, at least one metal component and / or at least one reinforcing component in particle form is advantageously provided. By a suitable selection of the structure, orientation, size and shape of the particles and their quantity, the material properties of matrix materials can be positively influenced. If appropriate, the formation of whisker crystals can also be promoted or prevented by suitable boundary conditions.

In a particularly advantageous manner, a first component can also be mixed with at least one further component before spraying. Gentle mixing, for example of cold spray particles, may be accomplished by coating the particles with a dispersion or suspension containing the reinforcing particles, followed by drying. Mixing in one Depending on the hardness of the particles, the ball mill or an attritor consisting of at least two different components under protective gas can cause the particle shape to be destroyed and thus adversely affect the flow behavior of the powder.

In such a method, within the scope of an advantageous embodiment, at least one organic and / or at least one ceramic reinforcing component can be used. This can be present in the sprayed mixture or can also be injected or co-injected.

With particular advantage, the reinforcing component used can be carbon in the form of nanotubes, fullerenes, graphenes, flakes, nanofibers, diamond or diamond-like structures. Composite particles such as single and multi-walled CNT (Single Walled / Multi Walled CNT, abbreviated SW / MW-CNT) with a length of 0.2 to 1000 μm, preferably of 0.5 to 500 μm and a bundle size of 5 to 1200 nm, preferably from 40 to 900 nm, have proven to be particularly advantageous. In order to improve their properties, SW-CNT or MW-CNT cold spraying particles can also be previously coated or coated with metals such as Cu or Ni by means of chemical processes. Another advantageous variant involves mixing and drying the metal powder with a CNT dispersion / suspension so that the metal powder particles are coated with the CNT. The proportion of SW-CNT or MW-CNT in the carrier gas or in the powder stream, for example, ranges from 0.1 to 30%, preferably from 0.2 to 10%.

With the aid of one of the spraying methods mentioned, it is possible to produce monovalent and multi-walled CNTs in a metal matrix integrate. According to the Applicant's investigations, an MMC coating or corresponding MMC strip with at least 0.3% SW or MW CNT produced in this way exhibits exceptional wear behavior with coefficients of friction and contact resistance values which are far below the previously known values of comparable metal layers.

An advantageous method involves using at least one reinforcing component selected from the group of tungsten, tungsten carbide, tungsten carbide cobalt, cobalt, boron, boron carbide, invar, kovar, niobium, molybdenum, chromium, nickel, titanium nitride, alumina, copper oxide, silver oxide , Silicon nitride, silicon carbide, silicon oxide, zirconium tungstate and zirconium oxide.

In this case, it is also possible to use a reinforcing component together with at least one further reinforcing component and / or to mix or mix it accordingly. Through the use of known ceramic components whose advantageous properties, in addition to those of other reinforcing components, can be exploited. By using boron, cobalt, tungsten, niobium, molybdenum and its alloys and Invar or Kovar, the thermal expansion coefficient of the composite can be positively influenced.

Advantageously, a metal matrix composite or coating having a metal matrix comprising at least one metal and / or alloy of a metal selected from the group of tin, copper, silver, gold, nickel, zinc, platinum, palladium may be used , Iron, titanium and aluminum is selected. As a result, for example, a special advantageous wear resistance, corrosion resistance and / or a specific electrical or thermal conductivity and an adapted coefficient of expansion can be provided.

A metal matrix composite material produced by the method according to the invention with a metal matrix having at least one metal component and at least one reinforcing component arranged in the metal matrix is likewise provided by the invention.

A metal matrix composite material which has a proportion of from 0.1 to 20%, preferably from 0.1 to 5%, preferably from 0.2 to 5%, of carbon nanotubes is regarded as being particularly advantageous. The abovementioned proportions have proven to be particularly advantageous in practice, as mentioned above.

A corresponding metal matrix composite having advantageous properties has, for example, a residual porosity of 0.2 to 20% with respect to the reinforcing component and / or from 0.2 to 10% with respect to the metal component. MMC with such residual porosities can be used with advantage when a particularly good abrasion resistance, such as in bearings or sliding surfaces, or a high electrical conductivity, such as in tracks, is required.

The metal matrix composite according to the invention is particularly suitable for a coating for a workpiece. The coating can, for example, on bearings and Sliding elements, heat sinks, connectors, punched grids and printed conductors, in particular on usable as heating elements printed conductors, are applied. Such MMC coatings can be made of, for example, Sn, Cu, Ag, Au, Ni, Zn, Pt, Pd, Fe, Ti, W and / or Al and their alloys such as solders, in particular with a content of SW-CNT or MW. CNT from 0.1 to 20%, preferably from 0.2 to 5%.

In particular, it may be a coated tape for use in electromechanical components such as connectors, springs, e.g. for relays, switching contacts, to act conductor tracks in punched grids and heating elements or heat sinks and elements. The metal strip preferably has a thickness of 0.01 to 5 mm, particularly preferably 0.06 to 3.5 mm. For the production of strips consisting only of the metal matrix composite material, it is also possible, as mentioned, for the components to be sprayed onto a non-wettable substrate such as films made of PEEK, polyimide or Teflon. Correspondingly produced stamped grids, tracks, heating elements and strips may comprise Cu, Al, Ni and Fe and alloys thereof.

Conductor tracks which have at least one metal matrix composite material produced as described above can be provided locally on a printed circuit board, MID structures (molded interconnection devices) made of, for example, LSDS or other thermoplastics, in particular via stencils, sprayed on or in the form of a laminar coating which, later, For example, by suitable photolithography process, further processed.

An MMC tape or trace may advantageously be made of Cu, Ag, Al, Ni and / or Sn and their alloys with a content of SW-CNT or MW-CNT of 0.1 to 20%, preferably 0.1 to 5 % consist.

With regard to further features and advantages, reference is expressly made to the statements relating to the production method according to the invention.
A metal matrix composite material produced in accordance with the method of the invention is particularly suitable for use in the production of workpieces, in particular electromechanical components. Such a use may either involve making the workpiece completely out of the metal matrix composite or coating it with such material.

characters

Figur 1

in schematischer Darstellung eine Vorrichtung zum Kaltgasspritzen, die zur Durchführung eines Verfahrens gemäß einer besonders bevorzugten Ausführungsform der Erfindung geeignet ist, und

Figur 2

mikroskopische Schliff-Aufnahmen der Gefüge und rasterelektronenmikroskopische Aufnahmen der Oberflächen von Metallmatrix-Verbundwerkstoffen, die mittels Verfahren gemäß besonders bevorzugter Ausführungsformen der vorliegenden Erfindung hergestellt sind.

The invention and its advantages as well as further embodiments of the invention are explained in more detail below with reference to the embodiments illustrated in the figures. In detail shows:

FIG. 1

a schematic representation of a device for cold gas spraying, which is suitable for carrying out a method according to a particularly preferred embodiment of the invention, and

FIG. 2

Microscopic micrographs of the microstructures and scanning electron micrographs of the surfaces of metal matrix composites, which are particularly preferred by methods according to Embodiments of the present invention are made.

A suitable apparatus for carrying out the method according to a particularly preferred embodiment of the invention for cold gas spraying is in FIG. 1 shown. The device has a vacuum chamber 4 in which, for example, a substrate 5 to be coated can be placed in front of the nozzle of a cold gas spray gun 3. It should be understood, however, that such a spraying process could also be carried out at atmospheric pressure, for which a vacuum chamber is not required. The placement of the workpiece 5 in front of the cold gas spray gun 3, for example, by means of an in FIG. 1 for clarity, not shown bracket. Preferably, the substrate 5 is movable, that is arranged displaceable and rotatable, so that a coating can be carried out at several positions, in particular band-shaped or flat. Alternatively or additionally, the cold gas spray gun 3 may be movably arranged.

For carrying out the coating of the substrate 5, the vacuum chamber 4 is evacuated and generated by means of the cold gas spray gun 3, a gas jet, are fed into the particles for coating the workpiece 5.

Here, the main gas stream, for example, a helium-nitrogen mixture with about 40 vol .-% helium passes through the gas supply line 1 in the vacuum chamber 4. The spray particles, such as a metal powder mixed with CNT, arrive in the auxiliary gas flow via the feed line 2 into the vacuum chamber 4, in which a pressure of about 40 mbar, and there in the cold gas spray gun 3. The leads 1, 2 are for this purpose led into the vacuum chamber 4, in which both the cold gas spray gun 3 and the substrate 5 is located. It can also be provided to supply a plurality of components to be sprayed via a plurality of auxiliary gas streams. The entire cold gas spraying process thus takes place in the vacuum chamber 4. The particles are accelerated so much by the cold gas jet that adhesion of the particles on the surface of the workpiece 5 to be coated is achieved by converting the kinetic energy of the particles into thermal energy. The particles can additionally be heated up to the maximum temperature indicated above.

The carrier gas, which passes during the cold gas spraying together with the spray particles from the spray gun 3 and carries the spray particles to the workpiece 5, passes after the injection process in the vacuum chamber 4. The spent carrier gas is removed via the gas line 6 from the vacuum chamber 4 by means of the vacuum pump 8. Between the vacuum chamber 4 and the vacuum pump 8, for example, a particle filter 7 is connected, which removes free spray particles from the spent carrier gas in order to prevent the spray particles from damaging the pump 8.

In the subfigures 2A to 2C of FIG. 2 are results of experiments in which each metal powder were injected with the addition of reinforcing components. The figures show images of cuts and scanning electron micrographs of the surface of the layers obtained thereby. In the experiments, commercially available Cu, SnAg ₃ and Sn powders were used used together with suitable MW-CNT from the manufacturer Ahwahnee (P / N ATI-BMWCNT-002).

FIG. 2A Figure 3 shows the microstructure of a layer 200 obtained by spraying 1.5% MW-CNT pure copper with a copper matrix 201 and CNT 202 discontinuously distributed therein at 1000X magnification. Furthermore, in the coating 200 so-called oxide skins 203 formed on the Cu grains by a not completely avoidable oxidation of the Cu powder during the mixing process with the MWCNT can be seen. The layers were injected at a nozzle exit temperature of 600 ° C and a pressure of 38 bar under N ₂ gas. The density of the layer is 99.5%, its thickness is 280 microns, the layer hardness is 1200 N / mm ² . Due to the good friction behavior, this layer is suitable as a running surface of bearings and bushes. After detachment of the 280 micron thick layer of the carrier material is a tape, which can be used as a conductor in stamped or electromechanical components use.

FIG. 2B Figure 3 shows the surface of a layer 210 of a tin matrix obtained by spraying pure Sn with 2.1% MW-CNT and CNT discontinuously distributed therein at 300x magnification. Figure 2C shows a detailed view of FIG. 2B in 10,000 times magnification. The layer 210 has spherical Sn bodies 213 with CNTs 202 distributed therebetween. The density of the layer is 99.4%. It has a hardness of 368 N / mm ² and a coefficient of friction of 0.5 in the wear test. When spraying this layer under N ₂ gas at a pressure of 32 bar and a nozzle exit temperature of 350 ° C, a layer thickness of 5 microns was achieved. By variation of the Nozzle exit temperature, travel speed and pressure, the layer thickness, the layer hardness and in combination with the CNT content of the powder, the coefficient of friction can be significantly changed (reduced). Such produced layers can be optimized by a post-treatment such as leveling or remelting (reflow treatment) in their surface structure specifically targeted to the particular application. Partially or fully applied to Cu alloy strips, these layers can be used to reduce plugging and drawing forces in electromechanical components such as connectors, or after appropriate leveling and reflow steps to improve the wear behavior of plain bearings and bushes.

Claims (14)

A method for producing a metal matrix composite material (200, 210) having a metal matrix (201, 211) comprising at least one metal component and at least one reinforcement component (202) arranged in the metal matrix (201, 211), characterized in that at least one of the components a spraying process is sprayed onto a substrate (5). A method according to claim 1, characterized in that as spraying cold gas spraying, flame spraying and / or plasma spraying is used. Method according to claim 1 or 2, characterized in that a film or a substrate with a non-wettable surface or a workpiece to be coated, a semifinished product and / or a 3D structure is used as the substrate (5). Method according to one of the preceding claims, characterized in that at least one surface of the substrate (5) and / or the metal matrix composite material (200, 210) is processed. Method according to one of the preceding claims, characterized in that at least one metal component and / or at least one reinforcing component (202) is provided in particle form. Method according to one of the preceding claims, characterized in that a first component is mixed before spraying with at least one further component. Method according to one of the preceding claims, characterized in that at least one organic and / or at least one ceramic reinforcing component (202) is used. Method according to one of the preceding claims, characterized in that as at least one reinforcing component carbon in the form of nanotubes (202), nanofibers, graphenes, fullerenes, flakes or diamond is used. Method according to one of the preceding claims, characterized in that at least one reinforcing component is used, which consists of the group of tungsten, tungsten carbide, tungsten carbide-cobalt, cobalt, copper oxide, silver oxide, titanium nitride, chromium, nickel, boron, boron carbide, Invar, Kovar, Niobium, molybdenum, alumina, silicon nitride, silicon carbide, silica, zirconium tungstate and zirconia. Method according to one of the preceding claims, characterized in that a metal component is used which comprises at least one metal and / or an alloy of a metal selected from the group of tin, copper, silver, gold, nickel, zinc, platinum, palladium, Iron, titanium and aluminum is selected. A metal matrix composite (200, 210) having a metal matrix (201, 211) comprising at least one metal component and at least one reinforcing component (202) disposed in the metal matrix (201, 211), the metal matrix composite (200, 210) being formed by a process manufactured according to one of the preceding claims. A metal matrix composite material (200, 210) in particular according to claim 11, which has a proportion of 0.1 to 20%, preferably 0.1 to 5%, preferably 0.2 to 5% carbon nanotubes (202) as a reinforcing component. A metal matrix composite (200, 210) according to claim 11 or 12, which has a residual porosity of 0.2 to 20% with respect to the reinforcing component and / or from 0.2 to 10% with respect to the metal component. Use of a metal matrix composite according to any one of claims 11 to 13 for manufacturing a workpiece, wherein the workpiece is coated by the metal matrix composite and / or formed from the metal matrix composite.

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