U.S. patent application number 10/662625 was filed with the patent office on 2004-05-20 for fiber-reinforced composite ceramic, fabrication method and lining material, armor, reflective surface and component having the composite ceramic.
Invention is credited to Benitsch, Bodo, Gruber, Udo, Ottinger, Oswin, Pfitzmaier, Eugen.
Application Number | 20040097360 10/662625 |
Document ID | / |
Family ID | 31895952 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040097360 |
Kind Code |
A1 |
Benitsch, Bodo ; et
al. |
May 20, 2004 |
Fiber-reinforced composite ceramic, fabrication method and lining
material, armor, reflective surface and component having the
composite ceramic
Abstract
A fiber-reinforced composite ceramic has a matrix containing SiC
and/or Si with a density of greater than 2.5 g/cm.sup.3 and an
elongation at break of more than 0.3%. A method for fabricating the
composite ceramic includes producing a blend containing carbon
fibers, carbonizable bonding resin and additional carbon material
which has a raw density in a range between 0.7 and 1.8 g/cm.sup.3,
pressing the blend into a fiber-reinforced green body, carbonizing
the green body in order to produce a C/C body, and infiltrating the
C/C body with a silicon melt. The fabricated composite ceramic is
used as a lining material or armor plating, or for producing
reflective surfaces.
Inventors: |
Benitsch, Bodo;
(Buttenwiesen, DE) ; Gruber, Udo; (Neusaess,
DE) ; Ottinger, Oswin; (Meitingen, DE) ;
Pfitzmaier, Eugen; (Thierhaupten, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, PA
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Family ID: |
31895952 |
Appl. No.: |
10/662625 |
Filed: |
September 15, 2003 |
Current U.S.
Class: |
501/99 |
Current CPC
Class: |
C04B 2235/80 20130101;
F27D 1/0006 20130101; C04B 2235/608 20130101; C04B 2235/526
20130101; C04B 2235/728 20130101; C04B 2235/422 20130101; C04B
2235/405 20130101; F27D 1/0009 20130101; C04B 2235/428 20130101;
C04B 35/573 20130101; C04B 35/565 20130101; C04B 35/583 20130101;
C04B 2235/404 20130101; C04B 2235/5292 20130101; F41H 5/0414
20130101; C04B 2235/77 20130101; C04B 2235/96 20130101; C04B
2235/425 20130101; C04B 2235/48 20130101; C04B 2235/5436 20130101;
C04B 35/83 20130101; C04B 2235/5296 20130101 |
Class at
Publication: |
501/099 |
International
Class: |
F41H 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2002 |
DE |
102 42 566.3 |
Claims
We claim:
1. A fiber-reinforced composite ceramic, comprising: a matrix
containing at least one of SiC and Si; a density of greater than
2.5 g/cm.sup.3; and an elongation at break of greater than
0.3%.
2. The fiber-reinforced composite ceramic according to claim 1,
which further comprises carbon reinforcing fibers.
3. The fiber-reinforced composite ceramic according to claim 1,
which further comprises a porosity of less than 5%.
4. The fiber-reinforced composite ceramic according to claim 1,
which further comprises a SiC proportion of greater than 60%.
5. A method for producing fiber-reinforced composite ceramic, which
comprises the following steps: a) providing a matrix containing at
least one of SiC and Si; b) producing a blend containing carbon
fibers, carbonizable bonding resin, and additional carbon material
having a raw density in a range of 0.7 to 1.8 g/cm.sup.3; c)
molding the blend into a fiber-reinforced green body; d)
carbonizing the green body to produce a C/C body; and e)
infiltrating the C/C body with a silicon melt.
6. The method according to claim 5, which further comprises
initially reacting the additional carbon material with the silicon
in step e), before the carbon fibers and the carbonized bonding
resin.
7. The method according to claim 5, which further comprises
providing the additional carbon material in the blend in step b) in
a proportion of between 2 and 35% by mass.
8. The method according to claim 5, which further comprises forming
the additional carbon material by pressing expanded graphite into
films and subsequently pulverizing the films.
9. The method according to claim 5, which further comprises
providing the additional carbon material as platelet-shaped
carbonaceous particles.
10. The method according to claim 9, which further comprises
providing the platelet-shaped particles with an average size of
under 500 .mu.m.
11. The method according to claim 9, which further comprises
providing the platelet-shaped particles with a height/diameter
ratio of greater than 50.
12. The method according to claim 8, which further comprises
forming the expanded graphite by the thermal decomposing of
intercalation compounds formed of graphite and at least one acid
selected from the group consisting of sulfuric acid, nitric acid
and perchloric acid.
13. The method according to claim 8, which further comprises
providing the expanded graphite with a raw density in a range of
0.7 to 1.3 g/cm.sup.3.
14. The method according to claim 8, which further comprises
providing crushed powder of precompressed expanded graphite with a
bulk density of 0.04 to 0.18 g/cm.sup.3.
15. The method according to claim 5, which further comprises
post-compressing the additional carbon material up to a maximum
density of 1.6 g/cm.sup.3 under pressing conditions for producing
the green body.
16. The method according to claim 5, which further comprises
providing bundled carbon fibers with an average length of less than
80 mm.
17. A lining material for combustion chambers or furnaces,
comprising a composite ceramic according to claim 1.
18. An armor protecting against ballistic effects or projectile
shots, comprising a composite ceramic according to claim 1.
19. A reflective surface, comprising a composite ceramic according
to claim 1.
20. A component for precision machines or calibration elements,
comprising a composite ceramic according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
[0002] The invention relates to fiber-reinforced composite ceramic
with a matrix containing silicon carbide (SiC) and/or silicon (Si).
The invention also relates to a method for fabrication of the
composite ceramic. The invention additionally relates to lining
material, armor, reflective surfaces and components having the
composite ceramic.
[0003] German Published, Non-Prosecuted Patent Application DE 197
10 105 A1, corresponding to U.S. Pat. No. 6,030,913, describes a
composite ceramic that is reinforced with high-tenacity graphite
short fibers. The ceramic has a matrix substantially formed of SiC,
in other words a C/SiC material. The matrix of the ceramic
composite material is formed substantially through the use of the
liquid silication of a carbon prebody with a silicon melt. The
reinforcing short fibers are surrounded by at least two sheathes
formed of graphited carbon, which is formed by carbonizing and
graphiting impregnation agents, particularly synthetic resin or
pitch. At least the outermost sheathe thereof is converted into
silicon carbide by reaction with liquid silicon. The fiber bundles
that are utilized for reinforcement are obtained by compressing
fiber prepregs at least once with a carbonizable impregnating
agent, carbonizing and graphiting them, and then milling them into
short-fiber bundles. The milled fiber bundles are mixed with
fillers and binders and pressed into green bodies, which are then
carbonized and infiltrated with liquid silicon. The resulting
composite material exhibits a quasi-ductile fracture behavior with
an elongation at break of approximately 0.25 to 0.5%. The density
of the composite material equals 2.27 g/cm.sup.3.
[0004] When using the known method, it is impossible to increase
the density significantly through the use of increased SiC
formation, without substantially reducing the elongation at break.
However, for a series of applications, a high density (i.e. a low
porosity) and high elongation at break (or tenacity behavior) of
the C/SiC material are critical. For instance, low porosity and
high ceramic content are important when utilizing composite
materials for ballistic protection, for instance as flak plates, in
order to achieve a shot refracting effect. At the same time, a high
elongation at break is desirable for the material in order to
prevent brittle fractures when the projectiles hit. Besides that, a
low porosity (high density) plays an important role in
high-temperature applications, because air can reach the carbon
fibers through open pores and cause oxidation damage.
SUMMARY OF THE INVENTION
[0005] It is accordingly an object of the invention to provide a
fiber-reinforced composite ceramic, a fabrication method and a
lining material, an armor, a reflective surface and a component
having the composite ceramic, which overcome the
hereinafore-mentioned disadvantages of the heretofore-known
products and methods of this general type and in which the
composite material exhibits a high tenacity in addition to its high
density.
[0006] With the foregoing and other objects in view there is
provided, in accordance with the invention, a fiber-reinforced
composite ceramic, comprising a matrix containing SiC and/or Si. A
density of greater than 2.5 g/cm.sup.3 and an elongation at break
of greater than 0.3% are provided.
[0007] With the objects of the invention in view, there is also
provided a method for producing fiber-reinforced composite ceramic,
which comprises providing a matrix containing SiC and/or Si in a
step a). A blend containing carbon fibers, carbonizable bonding
resin, and additional carbon material having a raw density in a
range of 0.7 to 1.8 g/cm.sup.3 is produced in a step b). The blend
is molded or pressed into a fiber-reinforced green body in a step
c). The green body is carbonized to produce a C/C body in a step
d). The C/C body is infiltrated with a silicon melt in a step
e).
[0008] Raw density means the geometric density derivable by
measuring the mass of a precise sample volume. Density as used
below refers to raw density.
[0009] The method for fabricating the carbon-fiber-reinforced SiC
ceramic composite material with high density and a high elongation
at break includes, first, according to step b), the fabricating of
a pressable blend containing carbon fibers, particularly carbon
fiber bundles, carbonizable bonding resin and additional carbon
material.
[0010] The carbon fiber bundles are preferably formed by layered
carbon short fibers, which are typically held together in bundles
by polymer or carbon.
[0011] Phenol or furfuryl alcohol resins are preferably used as the
carbonizable bonding resin.
[0012] Unprotected fiber material, graphite, carbonized bonding
agents, carbonization residue, or the like, are preferably used as
the additional carbon material. The purpose of the additional
carbon material is to convert into SiC as a "sacrificial material"
at the outset of the silicon melt infiltration. A high SiC yield is
the object of the liquid silication process. Prior attempts to
achieve high composite material densities were based on the
assumption that the carbon material must include the highest
possible carbon content, such as graphite, for instance, in order
to be able to develop as much SiC as possible.
[0013] However, experiments conducted by the applicant of the
instant application have shown that natural graphite cannot be
added in sufficient quantities to generate a body with high
density. The sharp volume increase of the reaction product relative
to the starting substances Si and C that is associated with the
reaction of natural graphite into SiC would lead to swelling or
exploding of the composite material body given larger graphite
quantities. That is because a sharp volume increase of
approximately 135% occurs in the reaction between natural graphite
and silicon into SiC. With higher graphite quantities, that
behavior can lead to a change in geometry or even destruction of
the molding body.
[0014] It was observed that, besides its chemical reactivity, the
density of the carbon material in the C/C body that is provided for
silicon melt infiltration is specifically responsible for the
density of the SiC matrix that is formed therefrom and the residual
porosity of the ceramic composite material. It was determined that
the conversion of the carbon material by the liquid silication
leads to dense SiC, and the filling of the residual porosity of the
C/SiC body it forms, only when the density of the carbon material
is within defined limits. Additional carbon material with an
average density in a range from 0.7 to 1.8 g/cm.sup.3, preferably
from 0.7 to 1.6 g/cm.sup.3 and particularly from 0.7 to 1.3
g/cm.sup.3, is added to the pressable blend, according to the
invention. The density of the suitable carbon material is thus
appreciably below the density of natural graphite (2.25
g/cm.sup.3). The utilization of a carbon material with a density
within the range according to the invention also guarantees that
the conversion into SiC does not lead to a volume increase that
would damage the composite material.
[0015] Expanded graphite, preferably following an intermediate
compressing process, has a density within the cited range. Another
advantage of expanded graphite is its high reactivity in relation
to the silicon melt, which leads to uniform silication and short
reaction time. The expanded graphite is obtained by the thermal
decomposition of a graphite-intercalation product. Compounds based
on graphite/sulfuric acid, graphite/nitric acid, or
graphite/perchloric acid are particularly relevant in this regard.
Expanded graphite is also obtained in the form of a loose vermiform
substance from the short-term heating of graphite salts or graphite
inclusion compounds such as graphite hydrogen sulfates or graphite
nitrates or graphite perchlorates, as described in European Patent
Application EP 1 120 378 A2, corresponding to U.S. patent
Application Publication No. U.S. 2001/0018040 A1, for example.
Graphite films or plates can be generated by compressing the
expanded graphite. These films or plates of expanded graphite have
a raw density between 0.7 and 1.8 g/cm.sup.3. An expanded graphite
powder can be produced which processes well and which can be mixed
into molding materials homogenously in a dispersed fashion, by
pulverizing the precompressed expanded graphite with the aid of a
cutting mill, impact mill, or jet mill. The raw density of the
crushed powder generally only negligibly deviates from that of the
graphite films.
[0016] The crushed powder of precompressed expanded graphite
typically has a bulk density between 0.04 and 0.18 g/cm.sup.3. A
powder with a bulk density between 0.05 and 0.14, and particularly
between 0.06 and 0.1 g/cm.sup.3, is preferred.
[0017] In contrast, uncompressed and unmilled powder of expanded
graphite generally has a substantially lower bulk density of
approximately 0.002 to 0.008 g/cm.sup.3. That low density makes
processing subsequent to the cited process for fabricating
composite ceramics extraordinarily difficult.
[0018] Besides the density of the material, the particle size and
morphology of the additional carbon material are also important. In
particular, fiber-shaped or platelet-shaped reinforcing materials
lead to high reinforcing effects in composite materials. In a
preferred development of the invention, a platelet-shaped carbon
material is used. It is preferably formed from expanded graphite.
Expanded graphite that has been precompressed to a density of
approximately 1 g/cm.sup.3 is particularly preferred. The
precompression can be achieved by pressing the graphite into films,
for example. For their part, the graphite films can be easily
crushed to a defined particle size. The platelet-shaped particles
having a height/diameter ratio of over 50, preferably over 80, and
particularly over 120, are preferred. The morphology of the
preferred platelet-shaped carbon particles with a density of
approximately 1 g/cm.sup.3 is represented in FIG. 1.
[0019] Beyond that, the additional carbon material can also have a
fiber-shaped configuration. Specifically, carbon nanotubes are
fiber-shaped carbon materials with a suitable density and
reactivity.
[0020] The suitable average particle size of the carbon material,
particularly the platelet material, is under 500 .mu.m, preferably
in a range between 0.1 and 300 .mu.m, and particularly in a range
between 0.1 and 100 .mu.m. Particle size refers to the
agglomeration-free primary particle. The mass % of carbon material
is advantageously less than 45% in the moldable blend. Mass
percents in the range between 2 and 35% are particularly
preferred.
[0021] The molding of the moldable material according to step c)
usually occurs in a press, with it being possible to cure the
material thermally or catalytically. Other pressure molding methods
can also be used, depending on the consistency of the material. The
addition of expanded graphite, in particular, leads to a relatively
good sliding and flowing capability, so that injection molding or
related molding techniques can also be carried out.
[0022] In step d), the resulting green body is baked (i.e.
carbonized) at temperatures between 750 and 1200.degree. C. in the
absence of air in order to produce the carbonaceous porous prebody
(C/C body). During this process, the bonding resin is broken down
into carbon. The carbonization may also be carried out at
temperatures near 2400.degree. C. At these temperatures, the
graphiting of carbon that has not yet been graphited occurs.
[0023] In the final step e), the C/C body is infiltrated with a
silicon melt according to the conventional technique, preferably
through the use of wicks. At least part of the carbon of the C/C
body is converted into SiC. A ceramic composite material with a
matrix composed predominantly of SiC is thereby formed. Residual
silicon and residual carbon occur in the ceramic composite material
as additional matrix components. When expanded graphite is used as
the preferred added carbon material, a relatively low residual
silicon content can be set. The proportion of free silicon
(residual silicon) in the ceramic composite material according to
the invention is thus advantageously under 10% by mass. In the case
of an application as an anti-ballistic material or as a component
of armor plating, the mass % of Si is preferably set at less than
7%. High SiC contents can be achieved in correspondence to the low
residual silicon content. The proportion of SiC in the ceramic
composite material is advantageously more than 60% by mass. A high
SiC content is important particularly in anti-ballistic
applications. In this case, the proportion of SiC is preferably
above 70% by mass.
[0024] Beyond this, other metals besides silicon can be present in
the silicon melt that is provided for the infiltration, such as Fe,
Cr, W or Mo, the proportion of which in the melt typically does not
exceed 20%. Ti is particularly preferred as an additional carbide
forming metal. Silicon is also characterized as a metal in the
context of this application. The ceramic composite material that is
produced with the method according to the invention has a density
of over 2.5 g/cm.sup.3. This value refers to infiltration with pure
silicon. When silicon alloys containing metals of greater or lesser
density than silicon are used, these density ranges must be adapted
according to the theoretical values. The open porosity of the
fiber-reinforced ceramic composite material is under 5% and the
elongation at break is greater than 0.3%. The composite material
that is produced by the method according to the invention thus
advantageously combines a high material density (i.e. low porosity)
with a relatively high elongation at break.
[0025] The composite material is particularly well suited for
thermally loaded components under oxidizing or corrosive conditions
by virtue of the high density (low porosity). The low porosity
prevents air from diffusing in and causing oxidative damage to the
carbon reinforcing fibers. Typical fields of application are thus
linings for combustion chambers or furnaces.
[0026] Another application of the fiber-reinforced composite
ceramic according to the invention is in the field of armor
materials. It is known that ceramic materials make good plating
materials for armor and for protection against projectiles. More
specifically, the high material density of the composite material
that is produced by the method according to the invention results
in a favorable refracting effect. Material densities above 2.6
g/cm.sup.3 are preferred for anti-ballistic applications. The
fiber-reinforced ceramics according to the invention have a
substantially higher fracture toughness as compared to monolithic
ceramics.
[0027] A further application advantageously exploits the good
polishability of the composite material surfaces that comes from
the high material density. This permits the ceramic composite
material to be used in the fabrication of mirrors in lightweight
structures, particularly satellite mirrors. The mirror surfaces
then need not be coated with high-polishing glasses or silicon in
the customary manner.
[0028] The invention can also be applied to components for
precision machines and calibration bodies. In this case, the very
small and uniform thermal expansion of the composite material
according to the invention across a large temperature range is of
critical importance. Due to its high stability, rigidity, and wear
resistance, the composite material can also be used directly as a
structural element of heavily loaded machine components.
[0029] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0030] Although the invention is illustrated and described herein
as embodied in a fiber-reinforced composite ceramic, a fabrication
method and a lining material, an armor, a reflective surface and a
component having the composite ceramic, it is nevertheless not
intended to be limited to the details shown, since various
modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and
range of equivalents of the claims.
[0031] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the following examples and
accompanying drawings.
[0032] Table 1 represents mechanical characteristics such as
ultimate breaking strength, elongation at break, and density of
composite ceramics (specimens PF 413, 414, 450, 460) produced
according to the invention in comparison with a composite ceramic
that was produced by another method (specimens PF 420, 444), as a
function of the starting substances that were used in the blend and
the quantities thereof.
[0033] Carbon-coated short-fiber bundles, bonding resin in the form
of phenol resin, and expanded graphite with a density of
approximately 1 g/cm.sup.3 were utilized as the additional carbon
material for producing the blend in specimens PF 413, 414, 450 and
460, respectively. The specimens differ with respect to the
quantity of carbon-coated short-fiber bundles, carbon fibers,
expanded graphite and bonding resin. The different types of
short-fiber bundles (Type A and Type B) differ only in the filament
number and morphology of the fiber strands that are used to make
the fiber bundle.
[0034] The specimens PF 420 and 444 were produced with natural
graphite with a density of 2.25 g/cm.sup.3. Like the specimens
produced according to the method according to the invention,
carbon-coated short-fiber bundles were utilized in these specimens
as well.
[0035] The results show that, with the addition of expanded
graphite, there is an increase in the density of the composite
material from 2.26 g/cm.sup.3 to 2.75 g/cm.sup.3 relative to the
control specimen PF 420 (5% natural graphite, 47% phenol resin),
without a reduction in elongation at break or ultimate breaking
strength. The control specimen PF 444 shows that these results
cannot be achieved with the substantially denser natural graphite
(2.25 g/cm.sup.3). The specimens of the test series PF 444, which
contain 10% natural graphite, were sharply swollen and in part
completely destroyed by the reaction of the graphite into SiC.
1TABLE 1 Mechanical Characteristics of Specimens in Dependence on
Type and Amount of Starting Substance Proportion Density Proportion
Ultimate Specimen of Carbon Carbon of Phenol Breaking Elongation
No. Carbon Carbon Material Material Resin Strength at Break Density
PF . . . Fiber Material (%) (g/cm.sup.3) (%) (MFa) (%) (g/cm.sup.3)
413 Type A Expanded 4 1 48 44 0.25 2.56 48% graphite 414 Type A
Expanded 10 1 40 55 0.3 2.52 50% graphite 450 Type B Expanded 10 1
30 2.60 60% graphite 460 Type B Expanded 15 1 30 2.75 55% graphite
444 Type A Natural 10 2.25 40 Specimen body swelled 50% graphite
and destroyed
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 is a raster electron microscopy image of
platelet-shaped carbon particles with a density of approx. 1
g/cm.sup.3;
[0037] FIG. 2 is a micrograph of a control specimen without an
addition of carbon material, representing regions of silicon
carbide, silicon, carbon fibers, and pores; and
[0038] FIG. 3 shows a specimen PF 460, which is produced with
expanded graphite.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 2 thereof, there is seen a micrograph
which shows regions of silicon carbide 1, silicon 2, carbon fibers
3 and pores 4.
[0040] The influence of the expanded graphite is evident
particularly from a comparison of the microstructure (represented
as a micrograph) of the C/SiC ceramics with a graphite addition to
those without the addition of carbon material. Besides showing
phases of SiC 1 and carbon fibers or fiber bundles 3, the control
specimen in FIG. 2, in which no carbon material whatsoever was
added, shows relatively large regions of Si phases 2 or pores 4,
both of which are undesirable with respect to the required material
characteristics.
[0041] In contrast, the specimen PF 460 with an addition of 15%
expanded graphite shown in FIG. 3 still exhibits only very small
regions with Si phases 2. Furthermore, the number of pores 4 as
well as their cross-sectional area are substantially reduced. The
carbon fiber bundles are advantageously completely surrounded by a
dense SiC matrix almost without exception.
* * * * *