CARBON FIBER-REINFORCED CARBIDE-CERAMIC COMPOSITE COMPONENT

Abstract

A ceramic component is formed of at least one stack of two or more layers of one-directional non-woven carbon fiber fabrics embedded in a ceramic matrix containing silicon carbide and elemental silicon. All adjacent layers within the at least one stack directly adjoin each other. The at least one stack has a minimum thickness of 1.5 mm perpendicularly to the plane of the layers. The ceramic matrix permeates substantially the entire component.

Claims

1. A ceramic component, comprising: at least one stack having at least two layers of unidirectional carbon fiber nonwoven embedded in a ceramic matrix containing silicon carbide and elementary silicon; all mutually adjacent said layers within said at least one stack directly adjoining one another; said at least one stack having a thickness of at least 1.5 mm in a direction perpendicular to a plane of said layers; and said ceramic matrix substantially penetrating the ceramic component in its entirety.

2. The ceramic component according to claim 1, wherein said ceramic matrix has a homogeneous composition across the entire component.

3. The ceramic component according to claim 1, wherein consecutive said layers within said at least one stack differ from one another in terms of an orientation of carbon fibers thereof.

4. The ceramic component according to claim 1, wherein the component has an open porosity of no more than 3.5%.

5. The ceramic component according to claim 1, wherein the component has a fiber volume in a range of 50-65% of a volume of the component.

6. The ceramic component according to claim 1, wherein the component has a density of no more than 2.0 g/cm.sup.3.

7. The ceramic component according to claim 1, configured as a charging rack.

8. A composite component, comprising at least two ceramic components according to claim 1 integrally bonded to one another.

9. A method of producing a ceramic component, the method comprising the following steps: a) placing at least two unidirectional carbon fiber nonwovens, which are impregnated with a polymer or a polymer precursor, one directly on top of another; b) consolidating the carbon fiber nonwovens, which are placed one on top of the other, under increased pressure and increased temperature relative to ambient pressure and temperature to form a carbon fiber-reinforced plastic; c) carbonizing the carbon fiber-reinforced plastic at a temperature of between 600 C. and 1000 C. to form a carbon fiber-reinforced carbon; d) graphitizing the carbon fiber-reinforced carbon at a temperature of at least 1800 C. to form a graphitized carbon fiber-reinforced carbon; and e) siliconizing the graphitized carbon fiber-reinforced carbon in such a way that, on a surface of the graphitized carbon fiber-reinforced carbon that is in contact with liquid silicon, at least some of the carbon fibers at a face end of at least one of the carbon fiber nonwovens point towards said surface.

10. The method according to claim 9, which comprises post-treating the carbon fiber-reinforced carbon formed in step c) at least once by performing the following steps: C1) impregnating the carbon fiber-reinforced carbon with a liquid carbon supplier to form an impregnated carbon fiber-reinforced carbon; and C2) carbonizing the impregnated carbon fiber-reinforced carbon.

11. The method according to claim 9, wherein the polymer or the polymer precursor comprises a synthetic resin selected from the group consisting of phenolic resin, furan resin and cyanate ester.

12. The method according to claim 9, wherein the unidirectional carbon fiber nonwoven impregnated with a polymer or a polymer precursor is a prepreg selected from the group consisting of a phenolic resin prepreg, a furan resin prepreg and a cyanate ester prepreg.

13. The method according to claim 9, wherein the step of consolidating the carbon fiber nonwoven placed one on top of the other comprises curing the synthetic resin.

14. The method according to claim 9, which comprises mechanically processing the graphitized, carbon fiber-reinforced carbon in accordance with a desired shape of the ceramic component, thereby producing a molded body.

15. The method according to claim 14, which comprises interlocking at least two molded bodies such that, on respective boundary surfaces of the connected molded bodies that are in contact with one another, ends of at least some of the carbon fibers of the corresponding molded bodies point towards the boundary surfaces.

16. The method according to claim 9, which comprises forming the ceramic component as a charging rack.

Description

EXAMPLES

[0057] 20 layers of a UD prepreg were placed one directly on top of the other such that their orientations alternated in a 90 offset (i.e., 0/90). In this case, the UD prepreg consists of parallel carbon fibers that are impregnated with phenolic resin that has not yet been cured. According to the invention, the prepreg comprises absolutely no auxiliary threads or other components in the direction transverse to the fiber direction of the carbon fibers. One layer of this prepreg has a height or thickness of approximately 0.25 mm and a width of approximately 1.20 m. The laminate is cured in a flat press mold under 1 bar and at 140 C. for 8 hours. Any escaping resin is removed from the surface of the resultant CFRP plate and said plate is cut to size to form smaller test specimens having the dimensions 10 cm10 cm.

[0058] The CFRP plates are carbonized at 900 C. under protective gas (nitrogen). A test specimen of the carbonized plate was subjected to the following repressing procedure twice (example 1), and another test specimen was subjected to the following repressing procedure three times (example 2):

[0059] impregnating with pitch, and

[0060] re-carbonizing (900 C.).

[0061] The test specimens in example 1 and example 2 were then graphitized for 24 hours at approximately 2000 C. The graphitized CFRC test specimens were placed in a siliconizing chamber and siliconized at approximately 1700 C. In this case, the test specimens are inserted into a rack made of graphite, which is arranged in a graphite crucible containing a sufficient amount of silicon powder for the siliconizing process. In this case, the graphite rack ensures that the component is oriented relative to the silicon bath surface as per the invention, i.e. one edge of the plates is in contact with the Si melt during the siliconizing process, since the ends of some of the carbon fibers end at the edges.

TABLE-US-00001 Test specimen Test specimen example 1 example 2 AD (g/cm.sup.3) 1.90 1.80 Open porosity 2% 3% Si content 10% 8% C content 66% 71% SiC content 24% 21% Modulus of elasticity (GPa) 60 65 AD: density determined according to the Archimedes principle using water. Open porosity: was also measured by being determined according to the Archimedes principle. Si content: free silicon not bound to carbon. C content: free carbon not bound to silicon.

[0062] An oxidation test was carried out for the test specimen according to example 2. A weight loss of approximately 0.15% was identified over 8 hours at 400 C. in air, which corresponds to a weight loss per hour of approximately 0.02%.

[0063] In both test specimens, the enormously high content of free carbon is evident, which results from the high fiber volume ratio. This ultimately leads to a high modulus of elasticity and a low density, which, in combination with low oxidation sensitivity, surpasses the known ceramic materials. Furthermore, it is evident that an additional repressing process as per example 2 resulted in a higher modulus of elasticity. This is presumably because the carbon fibers are even better protected as a result, and therefore more of the fibers are preserved. The C content or SiC content in example 2 also indicates this.

[0064] The above description makes reference to several published documents. As far as they provide additional or supplementary information, they are herewith incorporated by reference.