DE10143015A1 - Method of making composite from porous fiber-reinforced carbon preform and metal alloy forming carbides involves forming silicon carbide layer on the capillaries, holding metal alloy above melting point and detaching silicon carbide layers - Google Patents

Abstract

Method of making composite from porous fiber-reinforced carbon preform and metal alloy forming carbides involves exposing preform to silicon or silicon compounds, forming silicon carbide layer with carbon from the preform on the capillaries, holding metal alloy above melting point and detaching silicon carbide layers. Preform porosity is adjusted to 10 vol% - 60 vol%, with capillary structure. Infiltration exploits capillary effect. The body is supplied with silicon and/or silicon compounds in a liquid or gaseous phase. A silicon carbide (SiC) layer is formed with carbon from the preform, to a thickness exceeding 10 mu m, on the capillaries. Preform carbon content is sufficient to leave free carbon available for metal carbide formation. Metal alloy is held above its melting point and the silicon carbide layers detach. Alloying components form metal carbide from the free carbon. Together with SiC and residual metal alloy, these fill out the matrix of the composite.

Description

The present invention relates to a method for producing a composite material, in which a porous preform made of fiber-reinforced carbon is provided in the a metal alloy with an alloy component forming a metal carbide in liquid phase is supplied.

With the aim of producing novel composite materials, attempts have been made Mix carbon fibers (C fibers) with metals, press them or metals into one infiltrate porous carbon matrix. Here two groups of ceramic Composites differentiated: on the one hand metal matrix composite (MMC) and Ceramic matrix composite (CMC). An MMC is a composite with one Metal matrix, while a CMC has a matrix of ceramic components.

A method with the features specified at the outset is known from EP 1 041 056 A2 known. It contains a carbon and composite material containing titanium and copper described a process for its production. The composite material contains Cu-Ti Alloys of various compositions and is used to manufacture Pantographs used for rail vehicles. There are different procedures for Production of C / C preforms and their infiltration described: Production of C / C Preforms without metal content; Production of a C preform from C / C with different Cu and Ti proportions; Production of a C / C preform with Ti components. process engineering Among other things, the C / C preforms are infiltrated with pure Cu-Ti alloys. The Ti The proportion in the alloy serves for better wetting of the carbon fibers.

The known methods require long process times and those produced afterwards Composite bodies tend to form local voids and delaminations. Also are infiltrate only relatively simple geometries.

The present invention is based on the object of a method for the production of a composite material with which the body / components of any geometry without the disadvantages indicated above can be produced.

This problem is solved with a method for producing a composite material, in which a porous preform made of fiber-reinforced carbon is provided in the a metal alloy with an alloy component forming a metal carbide in Liquid phase is supplied, which is characterized in that the porosity of the preform is set to 10 to 60 vol .-% with a capillary structure that the infiltration under Exploitation of the capillary action of the capillary structure of the preform takes place in that then this body silicon and / or silicon compound (s) in the liquid or in the Gaseous phase is (are) such that the capillaries of the preform a SiC layer formed with carbon of the preform with a thickness of the layer <10 μm have, the content of matrix carbon of the preform being set in such a way that after the formation of SiC, sufficient free carbon for metal carbide formation is available that afterwards the metal alloy above them Melting temperature is maintained that the SiC layers detach and the metal carbide forming Alloy component with free carbon forms metal carbide, and together with the detached SiC and the remaining metal alloy component and carbon the Fill in the matrix of the composite material.

The composite material produced by this process shows, depending on the metal alloy, excellent functional properties, such as high conductivity due to the metallic phases, as well as structural properties, such as low expansion coefficient, high fracture toughness, high temperature strength due to the fibers and low density. The phases that characterize the matrix of the composite material are here Metal carbides, carbon and pure metals and metal alloy components. An essential one Aspect of the method is that preforms, preferably C / C preforms, with high capillary action can be used and that thin SiC layers as Form the intermediate product before the actual production of the composite material.

The supply or infiltration of the metal alloy that forms a metal carbide Contains alloy component, in the liquid phase is essential by the porosity and the Capillarity of the preform is determined by the number and orientation of the fibers, by the fiber type and the modification of the carbon of the preform is set. For this the preform should have an open porosity of> 10 vol Capillaries have diameters in the range from 20 to 100 µm and have a microstructure which the fiber bundles are separated by micro cracks that act as capillaries.

An anisotropic structure using carbon tissue and a quasi-isotropic structure by using C-fibers is said to have just such properties in Lead composite material. An anisotropic structure is chosen, for example, if rapid infiltrations or pronounced directional dependencies of the property of the Composite are necessary.

The porosity of the preform should be in the range of 10 to 60% based on the volume of the Preform; this porosity ensures that this is due to capillary forces can be infiltrated, and that the preform still has sufficient stability.

The coating of the fibers of the fiber structure or the capillaries as The preform used is made by means of SiC, which is a gas or Liquid phase reaction is generated. Liquid, silicon-organic can be used for the coating Precursors such as polycarbosilanes or silazanes can be used, which are in the Pores of the preform infiltrated and then subjected to a temperature treatment until an SiC-containing layer is formed. Alternatively, silicon or Silicon compounds via the gas phase, such as by a CVD process, be deposited. The wettability and infiltrability of the porous preform, preferably the porous C / C preform is increased by this pretreatment, so that the Preform then depressurized, d. H. only by the capillary forces, and completely with the Metal alloy which has a metal carbide-forming alloy component, such as for example, a Cu-Ti alloy can be infiltrated. It has been shown that without one such SiC coating the melt is infiltrable or only very incompletely. In addition, uncoated preforms can be severely delaminated, resulting in a Destruction of the entire body can result. The infiltration of the metal alloy melt preferably takes place after a rapid heating with heating rates> 10 K / min Alloy under vacuum or protective gas. Such rapid heating rates are too prefer, because it contaminates the metals by dissolving residual gases in the Melt or a gas phase reaction is largely avoided.

In the deposition of silicon and / or silicon compounds as Si vapor the silicon carbide is formed in-situ on the surface of the C-containing preform.

By the holding time above the melting point of the particular one used Alloy composition can melt the porous, fiber reinforced carbon completely wet and infiltrate. At the interface of the deposited silicon carbide or the carbon, the alloy components are separated.

Investigations by the inventors have shown that the SiC coating in the form of a SiC formation on the preform, preferably a C / C preform, for the metal carbide formation responsible for. During the infiltration, the silicon carbide formed is removed from the Preform removed and dissolved in the residual melt. The formation of the metal carbide with the remaining free carbon of the preform is aimed at since the one used Metal melt segregated. Under optimized process conditions should be good Segregation a holding time of> 30 minutes can be used. It will assumed that silicon carbide acts as an inhibitor that inhibits the rate of formation of other carbides controls when these carbide-forming metals come into contact with carbon come. The SiC coating prevents, for example, an immediate reaction of Ti with the carbon, and therefore a pore seal that prevents the melt from flowing would prevent. Since the reaction between Ti and C is highly exothermic, the SiC layer can be controlled to release energy.

• - Die Benetzung der Preform durch die Legierungsschmelze ist nicht homogen und findet nur oberflächlich statt, d. h. nur im äußeren Randbereich der Preform.
• - Die Eindringtiefe der Legierungsschmelze ist gering und kann mit maximal 1 bis 3 mm Eindringtiefe in die Preform angegeben werden, da die Kapillarität der offenen Porosität für eine vollständige Infiltration nicht ausreicht. An der äußeren Oberfläche der Preform bleibt demzufolge die Legierung als erstarrte Schmelze zurück.
• - Eine gewebe-verstärkte C/C-Preform neigt zu einer starken Delaminierung der Gewebelagen, was zum Zerstören des gesamten Bauteils während der Infiltration führen kann.

Investigations have shown that when a metal alloy containing titanium is inserted, titanium carbide immediately forms at the interface with carbon if the preform is not coated. However, there are three major disadvantages that are to be avoided with the coating as used according to the invention:

• - The wetting of the preform by the alloy melt is not homogeneous and takes place only superficially, ie only in the outer edge area of the preform.
• - The penetration depth of the alloy melt is small and can be specified with a maximum penetration depth of 1 to 3 mm into the preform, since the capillarity of the open porosity is not sufficient for complete infiltration. As a result, the alloy remains on the outer surface of the preform as a solidified melt.
• - A fabric-reinforced C / C preform tends to delaminate the fabric layers, which can destroy the entire component during infiltration.

As already mentioned, the outer and in particular inner surface of the preform, preferably the C / C preform, initially with a carbide layer, in the form of Silicon carbide, coated. The inner surface of the preform can be caused by microcracks or pores the carbon matrix or be formed by fibers or fiber bundles and represents in their Entire capillaries. In the infiltration process, the primary SiC is from the Preform detached and absorbed by the penetrating melt. At the same time takes place the places of detachment of the primary coating secondary carbide formation, for example a TiC formation if titanium is used as a metal alloy component, instead of. For this reason it is a primary one for successful implementation SiC coating necessary, which is well on the one hand from the surface of the preform, d. H. the C / C- Surface, peels off, and secondly can dissolve well in the melt. Instead of primary SiC coating then occurs the secondary metal carbide coating, preferably a TiC coating.

A holding time of at least 30 minutes is above the for infiltration Melting temperature of the alloy advantageously to provide a complete, homogeneous Infiltration can be achieved. During the reaction infiltration,> 100% by mass of the Metal alloy melt, preferably a Cu-Ti melt, in relation to the Initial weight of the preform (C / C body), which preferably has a porosity> 10% by volume, used and implemented. Through this holding time of at least 30 minutes above the Melting point can be ensured that the melt of each Alloy composition completely wet the porous preform (C / C material) and can infiltrate. At the interface to the deposited metal carbide or carbon the segregation of the alloy components of the alloy melt takes place. Here is the The driving force of segregation is the reaction of the existing carbon with one Alloy component, for example titanium, to TiC. The remaining porosity will then filled with copper.

The metal alloy is preferably infiltrated in a vacuum, preferably in a vacuum Pressure <10 mbar instead. If necessary, it can also be infiltrated with a slight excess pressure, when working with argon as the atmosphere, then the pressure to about 1000 to 1100 mbar is set.

In addition to the above-mentioned titanium, carbide-forming metals moreover, chromium and vanadium, zirconium, hafnium, molybdenum, tungsten, niobium and Tantalum can be used. The other alloy component of the metal alloy should have a high thermal and / or electrical conductivity, such as copper, so that, for example, besides copper also Ag, Au and Al as alloy components can be used.

The preferred metals with high conductivity of the alloys used are besides Copper also name silver, gold and aluminum, which have a low melting point (approx. 1100 ° C or 660 ° C) and a high conductivity, furthermore a high ductility, i. H. have high deformability under mechanical stress. It turns out that the received Composite material has a higher elongation at break than, for example, C / SiC Composites (C / SiC means C-fiber reinforced SiC), because in addition to the SiC, the is brittle, ductile copper fills the porosity.

Aluminum with a low melting point of 660 ° C, a density of 2.7 g / cm ³ and a high thermal conductivity of 220 W / mK is advantageous when a low specific density is desired.

It has also been shown that by adding one or more metals to the binary metal alloys instead of, for example, pure copper, alloys can be produced are that have high conductivity; such additives would be zinc and Copper, which leads to brass formation, tin and copper, which leads to bronze formation leads. Nickel, lead, antimony, bismuth can also be added to the Modify properties of copper, for example to form Mixed crystal phases.

The finished composite is a matrix of metal carbide, SiC, and solidified residual melt from the other metal alloy partner in the Spaces marked. The fiber structure of the preform, preferably the C / C preform, remains largely intact. The SiC, i.e. H. the coating that was originally the inner and the outer surface of the preform coated can be found in the capillaries. It can be used as a dispersed phase in both the metal carbide boundary layer and in the solidified melt of the other alloy component, d. H. for a TiCu alloy solidified copper melt, can be identified. With the increasing proportion of that Metal carbide-forming alloy constituent in the starting melt can be the Increase the volume fraction of the metal carbide that forms. That means the Metal carbide layer increases in thickness at the interface to the C / C framework.

In an experiment, the method according to the invention was carried out with a porous one C / C preform as starting body using a Cu73Ti27 alloy with 5 atom% Tin. TiC and tin bronze are then formed. A formation of pure copper is omitted here.

The following should be noted about the fibers of the preform:
Carbon fibers are preferably used in so-called carbon-carbon preforms. In addition, there are ceramic, in particular carbide fibers, such as. B. SiC fibers in question, but they are very brittle. The high oxidation resistance and high conductivity of the composite material have an advantageous effect. Such carbide fibers should therefore be added if higher resistance to oxidation is required. C fibers can also be highly conductive. For this purpose, a graphitization must be carried out (at temperatures of approximately 2000 to 3000 ° C) in order to provide a conductive graphite from the amorphous carbon of the fibers. With a view to good conductivity, UHM fibers (fibers with an ultra-high modulus) are particularly suitable which, after graphitization, have conductivities of around 600 W / mK. These are highly rigid, but also brittle, pitch fibers.

Another group of fibers that can be used are PAN fibers that however a comparatively low conductivity of 15-100 W / mK, depending on the type, demonstrate. These fibers are advantageous because of their low price, as opposed to UHM fibers that cost many times over.

Advantageous embodiments of the method according to the invention are in the Subclaims specified. The resulting from the characteristics of the subclaims Advantages have already been explained in the above explanations.

Various exemplary embodiments of the invention are described below Procedure explained.

example 1 Step 1 Manufacture of a CFRP body

A CFRP panel was first used as the raw material by RTM technology in one Metal die made. The die consists of a resin chamber and Tissue chamber in which resin and carbon fabric are separated. For the production of the CFRP becomes a fabric structure (HT fibers, laying direction alternately below 0 ° / 90 °, Canvas fabric), consisting of 14 fabric layers (thickness 0.25 mm), under Nitrogen pressure (increasing from 0.1-5 bar) and a temperature of 100 ° C with phenolic resin infiltrated. The resin granulate softens in the resin chamber and is placed under the gas pressure in the Tissue chamber pressed and infiltrates the tissue there. The infiltration took about 30 minutes. The infiltrated tissue is then under pressure (20 bar) and temperature of 200 ° C hardened in the die. The CFRP body produced in this way had one Fiber volume fraction of approx. 60 vol.%. The CFRP manufacturing process takes a total about 3 h.

step 2 Production of the C / C preform

The cured preform was then pyrolyzed up to 1650 ° C. For this purpose, the CFRP body was placed in a graphite crucible and weighted with a graphite plate (surface weight approx. 10 g / cm ² ) in order to avoid delamination. The process lasted approximately 140 hours under a nitrogen atmosphere. The necessary porosity (approx. 15 vol.%) And capillary structure of the preform formed during the pyrolysis. The result was a delamination-free C / C plate as a preform, consisting of C fibers and matrix carbon (formerly phenolic resin).

step 3 Coating of the C / C preform by steam siliciding

This C / C preform (dimension 210 × 150 × 3.1 mm ³ ), with an open porosity of 15% by volume, was provided for the steam siliconization. The C / C preform was placed vertically in a graphite crucible and the Si powder was positioned separately on the crucible bottom. The spatial separation was important here, so that no silicon is infiltrated capillary into the preform and closes the pores. In the experiment, approx. 1 kg of silicon powder was heated in a vacuum at 1600 ° C (heating and cooling rate 150 K / h, vacuum, holding time 40 min) and thus Si steam was generated. SiC forms at the interfaces to the carbon in the capillaries of the preform. SiC was thus deposited on the outer and inner surface of the C / C preform and a homogeneous SiC coating is formed on the accessible C surfaces with a thickness of a few µm. Some SiC single crystals grew locally on the carbon. The mass uptake of the C / C preform by the steam siliconization and formation of SiC was 2.5 mass%.

Step 4 Infiltration of a Cu-Ti alloy

The infiltration of the Cu-Ti alloy with the atomic composition Cu73Ti27 was carried out in an argon atmosphere in a resistance-heated HT furnace above the eutectic melting point, at a temperature of 1100 ° C. The heating rate was 600 K / h, argon was used as the purge gas (flow rate <2 l / min). The pressure in Test room was between 1000-1050 mbar. For the experiment, the was coated C / C preform placed in a graphite crucible and covered with the powder of the metal alloy. The crucible was closed with a graphite plate. The powders were intimate beforehand mixed to allow a homogeneous melting. It became copper powder 78% by mass, corresponding to 104 g (grain size <44 µm, melting point 1083 ° C, purity 99%, Alfa Aesar, Karlsruhe) and titanium powder 22 mass%, corresponding to 29 g (type S, Grain size <45 µm, melting point 1727 ° C, purity 98.5 +/- 0.5%, from Chemetall GmbH, Frankfurt). A holding time at the maximum temperature was used for the infiltration inserted from 1 h. 100 mass% alloy (133 g) with respect to the C / C Mass used to close the porosity. The cooling rate from the holding temperature was also 600 K / h. An almost dense composite material (porosity <2 vol .-%) can be achieved. The infiltrated body showed no delaminations of the individual fabric layers.

The composite material consists of carbon (fibers and residual matrix carbon), pure Copper, TiC and SiC.

Comparative Example 1

In contrast to Example 1, an uncoated C / C preform was used, which was manufactured analogously, as described in steps 1 and 2. Infiltration with the Alloy Cu73Ti27 was carried out according to the same procedure as described in step 3. After Removing the C / C preform from the graphite crucible showed an incomplete Wetting of the solidified melt on the preform surface. The melt could only Penetrate the porosity of the preform near the surface (penetration depth <1 mm). The Preform showed strong signs of delamination. Individual layers of fabric were inside of the composite material.

Example 2

Analogously to Example 1, a coated C / C preform was used. As an alloy a mixture of copper (73 at%) and titanium (27 at%) was also used. This mixture was 5 atom% tin (grain size <44 microns, melting point 232 ° C, purity 99.8%, Alfa Aesar, Karlsruhe) added. The melting also took place under argon gas as described in Example 1. The maximum temperature was 1200 ° C selected, 30 min as hold time. The plate was examined by X-ray. in the Pure copper could not be detected by diffractogram. TiC and one formed CuSn alloy (bronze). The composite material consisted of carbon (fibers and residual matrix carbon), bronze, TiC and SiC.

The attached figures serve to further explain the process sequence and of the results obtained. In the figures:

Fig. 1 shows a flow scheme of the individual process steps, as well as the materials for producing composite materials according to the invention comprising a preform made of fiber-reinforced carbon (fiber / C), which is first coated with SiC and is finally infiltrated with a metal alloy (MeMe '). Here Me means carbi-forming metal and Me 'means Cu, Ag, Au, Al and alloys based on Me'. The respective materials are shown on the left, while the individual process steps are shown on the right. The process steps are explained directly in FIG. 1, so that reference is made directly to the information in FIG. 1.

Fig. 2 shows a Röntendiffraktogramm of the composite with the phases identified Cu, TiC, SiC and graphite of Example 1; there are no mixed crystal phases, ie the Cu-Ti alloy completely segregates to form pure copper and TiC.

Fig. 3 shows an electron micrograph in the range of a coated C- fiber having a SiC coating, which was applied via an Si-Dampfsilizierung, with clearly visible SiC single crystals on the fiber surface; the thickness of the coating is <10 µm.

Fig. 4 shows an electron micrograph of the material structure of the composite material in the area of an infiltrated capillary, wherein the dark hem is TiC and the black phase of the C / C content. SiC is both dispersed in the copper and in the TiC, a discrete phase separation can be seen; TiC can only be recognized at the interface with carbon.

Claims (18)

1. A method for producing a composite material, in which a porous preform made of fiber-reinforced carbon is provided, into which a metal alloy with an alloy component forming a metal carbide is fed in the liquid phase, characterized in that the porosity of the preform is reduced to 10 to 60 vol. % is set with a capillary structure, that the infiltration takes place using the capillary action of the capillary structure of the preform, that silicon and / or silicon compound (s) in the liquid or in the gaseous phase are then fed to this body in such a way that the capillaries of the preform have an SiC layer formed with carbon of the preform with a thickness of the layer <10 μm, the content of matrix carbon of the preform being set such that after the formation of SiC, sufficient free carbon is available for the metal carbide formation stands that after that the metal alloy is kept above their melting temperature in such a way that the SiC layers detach and the metal carbide-forming alloy constituent forms free metal carbide, and together with the detached SiC and the remaining metal alloy constituent and carbon fill the matrix of the composite material. 2. The method according to claim 1, characterized in that the composite material has at least 50% by mass of fibers and metal alloy components. 3. The method according to claim 2, characterized in that the composite material has at least 80% by mass of fibers and metal alloy components. 4. The method according to any one of claims 1 to 3, characterized in that the remaining alloy component is Cu, Al, Ag and / or Au. 5. The method according to claim 1, characterized in that for the production of porous preform is first a green body by pressing, winding or laminating of fibers and / or fabrics is produced with the addition of binder, the under protective gas for pyrolysis of the binder at a temperature of 800-1600 ° C is exposed. 6. The method according to claim 1, characterized in that as fibers High temperature resistant and / or highly heat conductive carbon fibers are used. 7. The method according to claim 6, characterized in that the preform is preferably graphitized at a temperature of 1600 to 3000 ° C. 8. The method according to claim 1, characterized in that ceramic as fibers Fibers are used. 9. The method according to claim 1, characterized in that the fibers are carbide Fibers are used. 10. The method according to claim 9, characterized in that as carbide fibers SiC fibers are used. 11. The method according to claim 1, characterized in that the residual porosity of the Composite is less than 5%, preferably less than 2%. 12. The method according to claim 1, characterized in that the metal alloy for Infiltration at a temperature above their melting temperature for at least Is held for 30 minutes. 13. The method according to claim 1, characterized in that the thickness of the SiC Layer is 1 to 5 microns. 14. The method according to claim 1, characterized in that as a metal alloy Cu-Ti alloy is infiltrated. 15. The method according to claim 14, characterized in that the Cu-Ti alloy is heated at a heating rate of> 10 K / min. 16. The method according to claim 14, characterized in that the liquid Cu-Ti Alloy by the capillary forces of the capillaries in a with silicon carbide coated C / C preform is infiltrated. 17. The method according to claim 14, characterized in that the TiC content of the Composite material is set by the Ti content of the Cu-Ti alloy. 18. The method according to claim 1, characterized in that as a metal alloy multiphase, copper-containing metal alloy is infiltrated.