DE10348123B3 - Production of a structural component with a protective layer from a carbon-fiber reinforced silicon carbide ceramic, useful in space and automobile technology - Google Patents

Abstract

Production of a structural component (10) from a C-fiber reinforced Si carbide ceramic, the component having a protective layer by:preparation of a pressed composition (2) including C fibers, drying resin, and C, filling a compression mold with the composition, which is compressed and simultaneously cured by heating to give a C-fiber reinforced synthetic plastic (CFP) body (8), which is carbonized to a C/C perform, which is infiltrated with molten Si to form the Si carbide ceramic.

Description

The The invention relates to a method for producing a component of a silicon carbide ceramic according to the preamble of the claim 1.

Fiber-reinforced silicon carbide ceramics (C / SiC ceramics) have been increasingly deployed there lately, where high temperatures and high wear loads prevail. typical Fields of application are on the one hand the space technology, whereby here the low specific gravity of the silicon carbide ceramics is crucial is, continues the chemical engineering and in the automotive industry the brake disc technology or the coupling technology.

Even though the fiber reinforced Silicon carbide ceramics are very resistant to wear, occur again and again use cases on which an additional Wear protection layer Such ceramic components is appropriate. This is especially true because of that on the surface embedded in such ceramic components carbon fiber bundles, the oxidize at a constantly high temperature under an oxygen atmosphere, Leaving gaps and thus the basis for abrasive Form wear.

Some proposals have already been made to counter this problem, which arises especially with brake discs and clutch discs. The DE 198 34 018 C1 describes a method for applying a silicon carbide layer, wherein a porous carbon layer is applied to a carbon base body or to a SiC base body and is subsequently infiltrated with silicon.

In the DE 100 14 418 C2 Also, a method is described by which a silicon and silicon carbide layer is applied to the surface of a C / SiC device. Here, a slurry liquid containing pyrolyzable material is applied to the carbon body or to a carbon fiber body, carbonized and converted into an SiC layer during infiltration with silicon.

Both mentioned methods provide a technically suitable wear and oxidation protection layer, the process engineering that leads to these protective layers is but a constant effort to reduce the process costs inferior.

Of the The invention is therefore based on the object, a fiber-reinforced C / SiC component to provide a protective layer against oxidation and wear and opposite the method known in the art by a cheaper Process technology can be produced.

The solution the object consists in a method with the features of claim 1.

• – Das Herstellen einer Pressmasse, die zumindest Kohlenstofffasern, Trockenharz und Kohlenstoff umfasst,
• – das Befüllen dieser Pressmasse in eine Pressform,
• – das Pressen der Pressmasse bei gleichzeitiger Aushärtung der Pressmasse durch einen Wärmeeintrag, wobei ein kohlenstofffaserverstärkter Kunststoffkörper (CFK-Körper) entsteht,
• – das Karbonisieren des CFK-Körper zu einer C/C-Preform (C/C = Kohlenstofffaserverstärkter Kohlenstoff) und
• – die Infiltration der C/C-Preform mit flüssigem Silizium, wobei die C/C-Preform mit dem Silizium zu Siliziumcarbid reagiert und die faserverstärkte Siliziumcarbid-Keramik (C/SiC-Keramik) bildet.

The method according to the invention for producing a component from a carbon fiber-reinforced silicon carbide ceramic comprises the following steps:

• The production of a molding compound comprising at least carbon fibers, dry resin and carbon,
• The filling of this molding compound into a mold,
• - The pressing of the molding compound with simultaneous curing of the molding compound by a heat input, wherein a carbon fiber reinforced plastic body (CFRP body) is formed,
• - carbonizing the CFRP body to a C / C preform (C / C = carbon fiber reinforced carbon) and
• - Infiltration of the C / C preform with liquid silicon, wherein the C / C preform reacts with the silicon to silicon carbide and forms the fiber-reinforced silicon carbide ceramic (C / SiC ceramic).

• – dass zur Darstellung einer Schutzschicht separat ein Vorkörper der Schutzschicht hergestellt wird, wobei der Vorkörper der Schutzschicht Kohlenstoff und/oder ein kohlenstoffbildendes Mittel, Trockenharz und ein Stabilisierungsmittel enthält (unter kohlenstoffbildende Mitteln werden alle Verbindungen verstanden, die bei einem Karbonisierungsvorgang unter Luftausschluss Kohlenstoff bilden),
• – der Vorkörper der Schutzschicht wird in der Pressform in derart positioniert, dass er bezüglich der Pressmasse die entsprechende Lage der späteren Schutzschicht einnimmt.
• – Der Vorkörper der Schutzschicht wird während des Pressens des CFK-Körpers ebenfalls ausgehärtet, wobei eine kontinuierliche Verbindung zwischen dem Vorkörper der Schutzschicht und dem CFK-Körper entsteht.

The method is characterized

• In that, to form a protective layer, a preform of the protective layer is produced separately, wherein the preform of the protective layer contains carbon and / or a carbon-forming agent, dry resin and a stabilizing agent (carbon-forming agents are understood as meaning all compounds which form carbon in a carbonization process in the absence of air) .
• - The preform of the protective layer is positioned in the mold in such a way that it assumes the appropriate position of the later protective layer with respect to the molding compound.
• - The preform of the protective layer is also cured during the pressing of the CFRP body, with a continuous connection between the preform of the protective layer and the CFRP body is formed.

The advantage of the method according to the invention is that a desired preform for the protective layer can be produced, wherein the material properties of this preform body can be adjusted so that they optimally satisfy the properties of the protective layer. The Production of this preliminary body of the protective layer is thus completely decoupled from the production of the molding compound of the actual component. It can thus be prepared for different requirements of the protective layer different precursor and integrated into the standard process.

Thereby, that the preform the protective layer already integrated in the CFRP body during pressing In addition, it is carbonated together with the CFRP body and infiltrated with the silicon. Additional CFRP curing steps, additional Carbonation steps or additional Silizierschritte, as in the prior art are necessary, omitted in the process according to the invention.

By the pressing of the preform the protective layer during pressing the CFRP body arises between the CFRP body and the preform the protective layer a flat Compound, for example, by the flow of the Dry resin is formed. This optimized connection between CFRP body and preform of the protective layer furthermore has a positive effect on the connection between the protective layer in itself and the silicon carbide basic body.

Of the preforms The protective layer can in principle have different Processes are prepared which are suitable for handling and the transport of the preform to ensure. The preform the protective layer contains Carbon and / or a carbon-forming agent, which in a later Carbonization forms the carbon, dry resin, which is preferred similar to the dry resin used in the molding compound of the CFRP body is and a stabilizer. The stabilizing agent is used to, by a curing reaction the preform the protective layer to solidify that already mentioned transportability guaranteed is.

As Stabilizing agent is, for example, a cold-curing Binder, preferably based on polyurethane.

In In one embodiment of the invention, the proportion of the stabilizing agent on the preform between 2% by weight and 10% by weight. The proportion of stabilizer is thus relative to the proportion of dry resin in the preform relative low. The proportion of dry resin in the preform is optionally between 20% by weight and 40% by weight.

The Stabilizing agent is preferably designed such that it already at a curing temperature or below a curing temperature of CFRP body decomposes or softens. This ensures that the preform of the protective layer while pressing the CFRP body as well compacted and can enter into a two-dimensional connection with this.

advantageous Embodiments of the invention are based on the following figure explained in more detail.

there the sole figure shows the schematic sequence of the inventive method for Production of a component from a C / SiC ceramic.

The figure shows in its upper part two mixing devices 4 and 4 ' in which different molding compounds 2 and 2 ' be prepared. The molding compound on the left side comprises the components that make up the CFRP body that forms the basis for the future C / SiC ceramic. The components of the molding compound include carbon short fibers, carbon in graphite form and dry resin based on phenolic resin.

In the mixing device 4 ' on the right is a molding compound 2 ' for the production of the preform 12 for the protective layer 14 in the component 10 mixed. This molding compound 2 ' contains carbon in graphite form, milling residues of C / C bodies consisting essentially of carbon, phenol resin-based dry resin, and a polyurethane-based cold-curing binder serving as a stabilizer.

The The cold-curing binder used in this example is the so-called cold box method, which also in the production of casting cores Application finds. It is a mixture of the Components benzyl ether resin and polyisocyanate. The curing of this both components is carried out either by introducing a gaseous catalyst through the branched total gas-permeable pores of the mixture or by admixing a basic catalyst in the resin component (Self-curing).

As Catalysts are basic substances used, for example Amines such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, Triethylamine, dimethylethylamine, and mixtures thereof.

The preform 12 , which is now cured by the stabilizing agent that it is at least manageable, is now in the mold 6 inserted so that it has a top and a bottom of the molding compound 2 at least partially covering and so on with the later protective layer 14 of the component 10 forms. The component 10 may be formed in this example as a brake disc or as a brake disc blank.

In the mold 6 is now a press stamp 7 so on the molding compound 2 and the preform 12 pressed, whereby these are compressed together. In addition, the press stamps 7 heated in such a way that on the molding compound 2 and the preform 12 a temperature T acts. The temperature is about 130 ° C which leads to the melting of the dry resin, thereby further the molding compound 2 and the preform 12 be compacted. Due to the continuous compression of the molding compound of the ram is constantly tracked, so that as possible a constant pressure applied to the molding compound.

Thus, the preform is also 12 uniaxially in the vicinity of the molding compound, ie compressed in the pressing direction. In the present example, the preform is 12 shown as a circular disc, which is reduced in thickness by the compression and remains substantially constant in diameter. At the same time, the stabilizer decomposes in the preform 12 was used for a pre-hardening. The stabilizer decomposes in this case to carbon and gases, optionally from the mold 6 can escape.

After the pressing process and the curing process is from the mold 6 a CFRP body 8th taken. The CFRP body 8th on the one hand comprises the compacted molding compound 2 such as. the areas 13 , which represent the protective layer in the CFK state and from the preform 12 have emerged. The CFRP body thus comprises carbonizable binder in the form of the resin, carbon and carbon fibers.

The CFRP body 8th is now in a carbonator 16 In the absence of air, that is carbonated under vacuum or inert gas atmosphere to a C / C preform. The binder, which in this case is the phenolic resin, is reduced to carbon. The C / C preform consists essentially of carbon and carbon fibers.

Subsequently, the C / C preform is optionally processed and placed in an infiltration furnace 18 given. Here, the C / C preform is infiltrated with liquid silicon. The silicon runs into pore channels of the C / C preform, which are both in the area of the later protective layer 14 as well as in the body of the C / C preform are present. The silicon reacts with the carbon to form silicon carbide, the carbon fibers being protected in a suitable manner such that they do not react during infiltration with the silicon.

Either Carbonation as well as infiltration can be carried out at a suitable temperature Litigation take place in a single oven. It would after carbonation, which takes place at a temperature of about 1000 ° C, the temperature increased only to the infiltration temperature of silicon, about 1600 ° C. Likewise For example, a continuous tunnel kiln may be provided, in which the carbonation takes place in a first process step and in a second process step, the silicization.

The component thus obtained 10 thus has a basic body 15 up, from the former molding compound 2 results and it includes a protective layer 14 made from the former molding compound 2 ' and the resulting preform 12 originated. There is a microstructure difference between the basic body 15 and the protective layer 14 , The protective layer 14 consists essentially of silicon carbide and silicon. The ratio of silicon and silicon carbide can be controlled as needed. Here it depends on the porosity of the preform 12 or the layer 13 in the carbonated state.

At a higher porosity of the protective layer 13 in the C / C state has the protective layer 14 a higher proportion of silicon. With a lower porosity of the protective layer 13 in the C / C state, the proportion of silicon carbide in the protective layer increases 14 because more carbon is available to react with the silicon.

In general, the protective layer contains 14 no fibers. Fiber residues, optionally in the form of milling residues of the molding compound 2 ' As a rule, the silicon infiltration reacts completely with silicon carbide. Due to the composition of the protective layer 14 Made of silicon and silicon carbide, coupled with the absence of carbon fibers, the wear resistance of this protective layer 14 opposite the C / SiC base body 15 clearly increased.

The C / SiC base body 15 points opposite to the protective layer 14 due to its reinforcement by carbon fibers a much higher tensile strength and flexural strength. Thus, the body carries 15 to the damage tolerance and strength of the component, in this case, a brake disc, in which the relatively thin protective layer 14 , which has a thickness of about 1 to 10 mm, is responsible only for the wear resistance in the particularly wear-loaded regions on the surface, in particular on the friction surface with brake pads.

Claims (7)

Method for producing a component ( 10 carbon-fiber-reinforced silicon carbide ceramic, the component having a protective layer, comprising the steps of: - producing a molding compound ( 2 ), comprising carbon fibers, dry resin and carbon, - filling a mold ( 6 ) with the molding compound ( 2 ), - pressing the molding compound ( 2 ) with simultaneous curing of the molding compound ( 2 ) by heat input (T) to a CFRP body ( 8th ), - carbonizing the CFRP body ( 8th ) to a C / C preform and - infiltration of the C / C preform with liquid silicon to form the silicon carbide ceramic, characterized in that - a preform ( 12 ) of the protective layer ( 14 ), comprising carbon and / or a carbon-forming agent, and dry resin and a stabilizer, is prepared separately, - the preform ( 12 ) of the protective layer ( 14 ) in the mold ( 6 ) with regard to the molding compound ( 2 ) according to the position of the later protective layer ( 14 ) and - the preform ( 12 ) of the protective layer ( 14 ) also cures during pressing and with a CFRP basic body ( 15 ) enters a surface connection. Method according to claim 1, characterized in that that the stabilizing agent is below a curing temperature the molding compound decomposes or softens. Method according to claim 1 or 2, characterized in that a cold-curing binder is used as the stabilizing agent becomes. Method according to one of claims 1 to 3, characterized in that the stabilizing agent is a polyurethane-based cold-curing binder is used. Method according to one of claims 1 to 4, characterized the proportion of the stabilizing agent on the preform of the Protective layer between 2 wt.% And 10 wt.% Is. Method according to one of claims 1 to 5, characterized that the proportion of the dry resin on the preform of the protective layer between 20% by weight and 40% by weight. Method according to one of the preceding claims, characterized in that a dry resin based on phenolic resin is used becomes.