DE10143015C2 - Process for the production of a composite material - Google Patents

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.

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 material with a metal dimension trix, while a CMC has a matrix of ceramic components.

DE 25 56 679 C2 describes a composite material and a method for its manufacture position. The composite material consists of coals arranged in a metal matrix fabric fibers, wherein the matrix consists of a carbide-forming metal or such contains, especially from the group aluminum, magnesium, titanium, nickel, alloys of these elements as well as alloys, which one of these elements in a larger Share included. The carbon fibers are covered with a thin, carbide-containing coating Protection and possibly coated as a wetting layer. The surface coating the carbon fibers are said to consist of silicon oxide and silicon carbide. The layer be is made of silicon carbide and silicon oxide in a ratio of 1: 1 and is deliberately used for production of a silicon oxide deposited in an oxygen-rich atmosphere.

JP 0507866 A. In: Patent Abstracts of Japan [CD-ROM], describes the production a preform for a carbon fiber reinforced composite material. On the surface  a carbide is formed of the carbon fiber / carbon composite material. The preform and / or the carbon fiber reinforced metallic composite material are on the Carbon fiber / carbon composite material bonded.

EP 1 041 056 A2 relates to a carbon and composite material containing titanium and copper rial and a method of manufacturing the same. According to this document, a titanium and Carbon-containing carbon composite material and a process for its production described. The composite material contains Cu-Ti alloys of various types composition and is used to manufacture pantographs for rail vehicles used. It describes various processes for the production of C / C preforms and their infiltration described: production of C / C preforms without metal content; here provision of a C preform made of C / C with different Cu and Ti contents; manufacturing a C / C preform with Ti components. In terms of process engineering, the C / C Preforms infiltrated with pure Cu-Ti alloys. The Ti content in the alloy is used 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, the porosity of which is adjusted to 10 to 60% by volume with a capillary structure,
that silicon and / or silicon compound (s) are (are) supplied to this body in the liquid or in the gaseous phase 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 of <10 μm .
the content of matrix carbon of the preform being adjusted such that sufficient Si is available for metal carbide formation after the formation of SiC,
that a metal alloy with an alloy constituent forming a metal carbide is then heated at a heating rate of <10 K / min under vacuum or protective gas and fed to the preform as a liquid phase, the infiltration taking place using the capillary action of the capillary structure of the preform,
that the metal alloy is then held above its melting temperature for at least 30 minutes in such a way that the SiC layers detach and the metal carbide-forming alloy constituent forms free metal carbide with free carbon, and this metal carbide together with the detached SiC and the remaining metal alloy constituent and unreacted residual Carbon fills the matrix of the composite.

The composite material produced by this process shows, depending on the metal alloy, excellent functional properties, such as high conductivity due to the metal 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 metal carbons de, carbon and pure metals and metal alloy components. An essential one Aspect of the method is that preforms, preferably C / C preforms, with ho fro capillary action and that thin SiC layers are used as an intermediate form the product before the actual production of the composite material.

The supply or infiltration of the metal alloy, the alloy forming a metal carbide contains in the liquid phase is essentially due to the porosity and 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 .-%, a through diameter of the capillaries 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 through the use of C-fibers is said to have 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 initial pro The preform used is made by means of SiC using a gas or liquid phase action is generated. Liquid, silicon-organic precursors can be used for the coating ren, such as polycarbosilanes or silazanes, used in the Po Ren infiltrated the preform and then subjected to a temperature treatment until an SiC-containing layer is formed. Alternatively, silicon or silicon ver Connections via the gas phase, such as by a CVD process, are fired that will. 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, as in for example, a Cu-Ti alloy, can infiltrate. It has been shown that without a sol che SiC coating the melt is not or only very incompletely infiltrable. Au In addition, non-coated preforms can be severely delaminated, resulting in a disintegration whole body disorder.

After rapid heating, the metal alloy melt is infiltrated with Heating rates <10 K / min of the alloy under vacuum or protective gas. Through such Rapid heating rates will contaminate the metals by dissolving residual gases in the melt or a gas phase reaction largely avoided.

In the deposition of silicon and / or silicon compounds as Si vapor he this is followed by the in-situ formation of silicon carbide on the surface of the C-containing preform.  

Due to the holding time above the melting point of the respective alloy used composition, the melt can fully contain the porous, fiber-reinforced carbon constantly wetting and infiltrating. 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 pre Detached form 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 metal used melt segregated.

A holding time of <30 minutes is used for good segregation. 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.

Studies have shown that when a titanium-containing metal alloy 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, d. H. only in the outer edge area of the preform.
• - The depth of penetration of the alloy melt is small and can be a maximum of 1 to 3 mm Depth of penetration can be given in the preform as the capillarity of the open Porosity is not sufficient for complete infiltration. On the outer surface the preform therefore remains the alloy as a solidified melt.
• - A tissue-reinforced C / C preform tends to strongly delaminate the Ge woven layers, which leads to the destruction of the entire component during the infiltration can.

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 car bid, 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, the secondary carbide formation for example a TiC formation, if titanium is used as a metal alloy component, instead of. For this reason, a primary SiC coating is necessary for the successful implementation tion 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 melting point for the infiltration 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, with respect to the out 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 the respective alloy composition completely wet and infiltrate the porous preform (C / C material)  can. 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 at a pressure of <1.10 ³ Pa (10 mbar). If necessary, it can also be infiltrated with a slight excess pressure when working with argon as the atmosphere, the pressure then being set to about 1.10 ⁵ Pa-1.1.10 ⁵ Pa (1000 to 1100 mbar).

In addition to the titanium mentioned above, carbide-forming metals can also be used from preferably 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, in addition to copper, Ag, Au and Al are also used as alloy components can be placed.

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 receive ne 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 Ren metal alloys instead of pure copper, for example, 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. Furthermore, nickel, lead, antimony, bismuth can be added to the own Modify copper properties, for example to form mixed crystal sen.

The finished composite is a matrix of metal carbide, SiC, and solidified residual melt from the other metal alloy partner in the space men 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 stared at melt of the other alloy component, i.e. H. for a TiCu alloy solidified copper melt, can be identified. With the increasing proportion of the Me The alloying constituent of tall carbide in the starting melt is volu Increase the proportion of 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 Atomic% 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. To do this, a graphitization step 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 Unteran sayings. The result from the characteristics of the subclaims parts have already been explained in the foregoing.

Various exemplary embodiments of the inventive method are described below driving 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 fabric came 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 0.01-0.5 MPa (0.1-5 bar)) and a temperature of 100 ° C with Phenolic resin infiltrates. The resin granulate softens in the resin chamber and is under the Gas pressure is pressed into the tissue chamber and infiltrates the tissue there. The infiltration took about 30 min. The infiltrated tissue is then under pressure (2 MPa (20 bar)) and temperature of 200 ° C hardened in the die. The herge in this way The CFRP body had a fiber volume fraction of approx. 60 vol.%. The process of CFRP production takes a total of about 3 hours.

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, about 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 er followed in an argon atmosphere in a resistance-heated HT furnace above the eutecti 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 the ver search space 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 delamination 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 Legie Cu73Ti27 was carried out according to the same procedure as described in step 4. After Removing the C / C preform from the graphite crucible showed an incomplete benet 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 Pre form 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. the 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 selects, 30 min as hold time. The plate was examined by X-ray. In the diffracto no pure copper could be detected. 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 diagram of the individual process steps and the materials for the production of composite materials according to the invention, comprising a preform made of fiber-reinforced carbon (fiber / C), which is first coated with SiC and then infiltrated with a metal alloy (MeMe ') becomes. 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 X-ray diffractogram of the composite material with the identified phases Cu, TiC, SiC and graphite from 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 area of a coated C-fiber with an SiC coating, which was brought up via Si steam silication, 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, the dark border being TiC and the black phase being the C / C portion. 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. Process for the production of a composite material,
in which a porous preform made of fiber-reinforced carbon is provided, the porosity of which is adjusted to 10 to 60% by volume with a capillary structure,
that silicon and / or silicon compound (s) are (are) supplied in the liquid or in the gaseous phase 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 of <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 formation of metal carbide,
that a metal alloy with an alloying constituent forming a metal carbide is then heated at a heating rate of <10 K / min under vacuum or protective gas and fed to the preform as a liquid phase, the infiltration taking place using the capillary action of the capillary structure of the preform,
that the metal alloy is then held above its melting temperature for at least 30 minutes in such a way that the SiC layers detach and the metal carbide-forming alloy component forms metal carbide with free carbon, and this metal carbide together with the detached SiC and the metal alloy component remains and non- reacted residual carbon fills the matrix of the composite. 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 the po 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 high-temperature fibers resistant and / or highly thermally conductive carbon fibers are used. 7. The method according to claim 6, characterized in that the preform at a Temperature from 1600 to 3000 ° C is graphitized. 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% 12. The method according to claim 11, characterized in that the residual porosity of the Composite is less than 2%. 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 through the capillary forces of the capillaries in a be with silicon carbide layered 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.