A fiber preform is partially infiltrated with a ceramic material. A porous solid polymer is formed by reaction forming the infiltrated preform which is then pyrolized. Microporous carbon in the composite matrix is converted into silicon carbide

Behrendt, Donald R.

Singh, Mrityunjay

English

NASA Technical Reports Server

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US005865922A 
United States Patent [19] [ i l l  Patent Number: 5,865,922 
Behrendt et al. [45] Date of Patent: Feb. 2,1999 
PRODUCING FIBER REINFORCED 
COMPOSITES HAVING DENSE CERAMIC 
MATRICES 
Inventors: Donald R. Behrendt, Strongsville; 
Mrityunjay Singh, Parma, both of 
Ohio 
Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 725,205 
Filed: Sep. 20, 1996 
Related U.S. Application Data 
Continuation of Ser. No. 265,902, Jun. 21, 1994, abandoned. 
Int. C1.6 ...................................................... B32B 31/00 
U.S. C1. ............................ 156/155; 156189; 1561245; 
4271228; 4271249; 4271375 
Field of Search ..................................... 4281110, 113, 
4281114, 294, 408, 698, 288, 367, 375, 
395, 333, 419.7, 431, 224, 902; 1561148, 
155, 89, 245; 4231447.3, 450; 4271228, 
249, 248.1, 367, 375, 394, 299, 333, 417.7, 
432, 294, 380, 419.2, 443.2 
References Cited 
U.S. PATENT DOCUMENTS 
4,275,095 611981 Warren .................................... 4271228 
4,970,123 1111990 
5,024,878 611991 
5,045,356 911991 
5,061,414 1011991 
5,067,998 1111991 
5,079,039 111992 
5,132,155 711992 
5,198,152 311993 
5,221,578 611993 
5,350,545 911994 
Witzke et al. .......................... 4281545 
Robinbrosse et al. .................. 4281297 
Uemura et al. ......................... 4271249 
Engle ..................................... 264129.5 
Liimatta et al. ................... 2521389.31 
Carpenter et al. ...................... 4281367 
Streckert et al. 264129.1 
OTHER PUBLICATIONS 
Patent Abstracts of Japan, vol. 17, No. 632, Nov. 24, 1993 
& JP 05 195318 A (Toray Monofilament Co., Ltd.), Aug. 3, 
1993. 
Primary Examineraer r ick  Dixon 
Attorney, Agent, or Firm-Kent N. Stone; Susan D. 
Reinecke 
[571 ABSTRACT 
A fiber preform is partially infiltrated with a ceramic mate- 
rial. 
A porous solid polymer is formed by reaction forming the 
infiltrated preform which is then pyrolized. Microporous 
carbon in the composite matrix is converted into silicon 
carbide. 
13 Claims, 1 Drawing Sheet 
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https://ntrs.nasa.gov/search.jsp?R=19990046085 2020-06-18T01:03:29+00:00Z
U S .  Patent Feb. 2,1999 5,865,922 
5,865,922 
1 
PRODUCING FIBER REINFORCED 
COMPOSITES HAVING DENSE CERAMIC 
MATRICES 
This application is a continuation of application Ser. No. 
081265,902 filed on Jun. 12, 1994, now abandoned. 
ORIGIN OF THE INVENTION 
The invention described herein was made by an employee 
of the U.S. Government together with an associate of the 
National Research Council and is subject to the provisions 
of Section 305 of the National Aeronautics and Space Act 
1958, Public Law 85-568 (72 Stat. 435, 42 U.S.C. 5 1457). 
1. Technical Field 
This invention is concerned with the production of fiber 
reinforced composites. The invention is particularly directed 
to fiber reinforced composites having dense ceramic matri- 
ces. 
Whisker reinforcement of matrices has been proposed in 
the prior art. However, problems have been encountered in 
the incorporation and the uniform distribution of whiskers in 
matrices. This leads to very high processing temperatures 
and pressures. In spite of these parameters, full densification 
is not easily achieved. 
It is, therefore, an object of the present invention to 
produce dense silicon carbide and silicon carbide-refractory 
disilicide matrices for fiber reinforced composites. 
Another object of the invention is to produce fiber rein- 
forced composites utilizing both small and large diameter 
Sic fibers. 
A still further object of the invention is to utilize whisker 
and particulate toughening mechanisms to improve ceramic 
matrices. 
An additional object of the invention is to utilize whisker 
and particulate reinforcement to matrices to tailor the ther- 
mal expansion coefficient with the fibers. 
2. Background Art 
U.S. Pat. No. 4,970,123 to Witzke et al, U.S. Pat. No. 
5,045,356 to Uemura et a1 and U.S. Pat. No. 5,024,878 to 
Robinbrosse et a1 are concerned with the densification of 
fiber reinforced ceramic. These patents show various means 
for chemical vapor infiltration and liquid infiltration. 
U.S. Pat. No. 5,061,414 to Engle and U.S. Pat. No. 
5,079,039 to Heraud et a1 are likewise concerned with the 
densification of fiber reinforced ceramics by chemical vapor 
infiltration. These patents additionally show multiple chemi- 
cal vapor infiltration application steps. 
DISCLOSURE OF THE INVENTION 
The aforementioned objects are achieved by using silicon 
carbide refractory materials as a matrix for a fiber reinforced 
material. A fiber preform is placed within a chamber to 
undergo chemical vapor infiltration. 
In the first step, chemical vapor infiltration is only par- 
tially carried out. This partial chemical vapor infilitration 
(CVI) treatment serves to rigidize the material as well as 
protect the fibers in subsequent processing. 
In the next step, a partially densified CVI preform is 
impregnated with a resin mixture, then converted by high 
temperature pyrolization to produce a microporous carbon 
matrix which is connected to high temperature pyrolization. 
In the final step, the porous matrix is infiltrated with liquid 
silicon which forms silicon carbide with the pores of the 
matrix, resulting in a very dense fiber reinforced matrix. 
2 
BRIEF DESCRIPTION OF THE DRAWING 
The advantage and novel features of the invention will be 
more fully apparent from the following detailed description 
when used in connection with the accompanying drawings 
in which 
FIG. 1 is a photomicrograph at a 50 magnification show- 
ing the microstructure of a partially densified chemical 
vapor infiltrated preform; 
FIG. 2 is a photomicrograph at a 50 magnification show- 
ing the microstructure of a densified composite; and 
FIG. 3 is a photomicrograph at a 50 magnification show- 
ing a microstructure of a densified composite. 
5 .  
10 
15 BEST MODE FOR CARRYING OUT THE 
INVENTION 
According to the present invention, a fiber preform of 
unidirectional fibers, 2-D woven fiber tows, or 3-D woven or 
braided fiber tows is positioned in a chamber that is suitable 
2o for chemical vapor infiltration (CVI). The preform is then 
partially densified by the CVI process with a suitable 
ceramic material to yield a rigid body having a relatively 
large volume fraction of interconnected pores. The material 
of infiltration may be Sic ,  Si,N,, or refractory disilicide. 
The CVI processing is done under conditions that will 
coat the fibers with a somewhat uniform coating of ceramic 
material. The purpose of this coating is twofold; the first 
being to render the body rigid for further processing, and the 
second to protect the fibers from damage by the further 
30 processing. The pore volume may be as small as 10 volume 
percent or as high as 60 volume percent. A typical micro- 
structure of this preform is shown in FIG. 2 wherein dark 
areas 10 show porosity. 
Subsequent processing steps involve the production of a 
near theoretically dense matrix. The partially chemical 
vapor infiltrated body is then processed by reaction forming 
in which the body is infiltrated with a resin mixture that is 
designed to produce the controlled microporous glassy car- 
4o bon matrix. The resin mixture is a relatively high char yield 
resin, a pore forming agent, and an acid catalyst to promote 
polymerization of the resin. 
When the resulting porous solid polymer is pyrolized to 
high temperature, the pore forming agent is removed by 
45 distillation and the solid polymer decomposes to a glassy 
carbon. The morphology of the glassy carbon has been 
varied from connected platelets, connected struts, to con- 
nected near spherical shapes. These morphology variations 
of the glassy carbon depend on the pore forming agent used, 
the time and temperature of polymerization, the type and 
amount of acid catalyst used, and other processing variables. 
The pore volume fraction of the matrix depends mainly on 
the amount of pore forming agent used in the resin mixture. 
The last step in this process is to convert the microporous 
55 carbon of the composites matrix into silicon carbide. This 
accomplished by infiltrating the body with liquid silicon or 
a liquid silicon alloy. 
The silicon readily infiltrates the porous body and reacts 
with the carbon to form silicon carbide. If an alloy of silicon 
60 is used, such as silicon-refractory metal alloys, the com- 
pound refractory disilicide is precipitated as the silicon 
reacts with the porous carbon. In either case, the final result 
is a dense matrix comprising silicon carbide and some free 
silicon and in the case of alloy infiltration, some additional 
65 precipitated disilicide. The amount of free silicon depends 
mainly on the volume fraction of pores in the pyrolized 
matrix. If the porous carbon matrix has a pore volume 
25 
35 
5,865,922 
3 
fraction of 0.562, the final siliconized matrix will have no 
free silicon. If it contains a larger amount of pores, there will 
be some free silicon in the final material. 
A typical microstructure of this densified composite is 
shown in FIG. 2. Fibers 12 reinforce a SiC+si matrix 14. 
Another typical microstructure of a densified composite 
14 is shown in FIG. 3. The fibers 12 reinforce the SiC+Si 
matrix 14. Canned porosity 16 appears between certain 
fibers. 
The aforementioned process has many advantages over 
other processes described for the processing of ceramic 
matrix composites. By way of example, the processing time 
is shorter and the processing temperature is lower than other 
techniques. Very complex shapes can be made by forming 
the reinforcing fibers or tows of fibers into the desired shape 
by braiding or other similar process. 
The use of tooling during the chemical vapor infiltration 
processing can further define the desired shape. The total 
processing is a near net shape method. The desired shape is 
determined in the CVI processing, and the subsequent 
reaction forming process produces only minor, if any, net 
shape changes. 
The process of the present invention produces a near 
theoretical dense matrix formed mainly of silicon carbide 
with a small controllable amount of free silicon. This is 
likewise true for the silicon-refractory metal alloy infiltra- 
tion with the addition of precipitated silicides in the matrix. 
It will be apparent to one skilled in the art that the process 
of the present invention can be used not only to densify 
bodies made by the CVI process, but other bodies made by 
other ceramic processing methods that produce a porous 
ceramic or ceramic matrix composite. Ceramic bodies or 
composites made by reaction-bonded silicon nitride, made 
by ceramic polymer precursors, or made by other processes 
that produce a material that is porous may be densified by 
the reaction forming process of the present invention. 
Numerous modifications and adaptations of the present 
invention will be apparent to those skilled in the art. Thus, 
it is intended by the following claims to cover all modifi- 
cations and adaptations which fall within the true spirit and 
scope of the invention. 
What is claimed: 
1. A method of producing fiber reinforced composites 
positioning a body of fibers in a chamber, 
having dense ceramic matrices comprising: 
4 
partially infiltrating the body of fibers with a ceramic 
material resulting in a rigid body having a relatively 
large volume fraction of interconnected pores, 
reaction forming the infiltrated body of fibers thereby 
forming a porous solid polymer, 
pyrolizing said porous polymer to form a microporous 
carbon matrix, and 
converting the microporous carbon in the composites 
matrix into silicon carbide. 
2. A method of producing fiber reinforced composites 
having dense ceramic matrices as claimed in claim 1 
wherein the fibers are a preform of unidirectional fibers. 
3. A method of producing fiber reinforced composites 
having dense ceramic matrices as claimed in claim 1 
4. A method of producing fiber reinforced composites as 
claimed in claim 1 wherein the fibers are 3-D woven fiber 
tows. 
5 .  A method of producing fiber reinforced composites 
having dense ceramic matrices as claimed in claim 1 
2o wherein the fibers are 3-D braided fiber tows. 
6. Amethod of producing composites as claimed in claim 
1 wherein the fibers are partially infiltrated by chemical 
vapor infiltration in said chamber. 
7. A method of producing reinforced composites as 
2s claimed in claim 6 wherein the fibers are partially infiltrated 
with a ceramic material selected from the group consisting 
of Sic ,  Si,N,, and refractory disilicides. 
8. Amethod of producing composites as claimed in claim 
7 wherein the body has a pore volume between 10 volume 
9. Amethod of producing composites as claimed in claim 
1 wherein the reaction forming comprises infiltrating the 
body of fibers with a resin mixture. 
10. A method of producing a composite as claimed in 
3s claim 9 wherein the resin mixture comprises a resin wherein 
said resin has a char yield of at least 50 percent, pore 
forming agent, and an acid catalyst to promote polymeriza- 
tion of the resin. 
11. A method of producing a composite as claimed in 
12. A process of producing a composite as claimed in 
claim 11 wherein the silicon is a liquid. 
13. A method of producing a composite as claimed in 
claim 12 wherein the body is infiltrated with a liquid silicon 
5 
10 
1s wherein the fibers are 2-D woven fiber tows. 
30 percent and 60 volume percent. 
4o claim 1 wherein the body is infiltrated with silicon. 
4s alloy. 
* * * * *  


Producing Fiber Reinforced Composites Having Dense Ceramic Matrices

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