Refractory composite materials protected against oxidising...

Details Refractory composite materials protected against oxidising... Refractory composite materials protected against oxidising...

1999-04-21

2001-12-18

Weisberger, Richard (Department: 2164)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S403000, C428S404000, C428S367000, C428S368000, C428S688000, C427S215000, C427S419100, C427S419700, C427S419800, C427S585000, C427S589000, C427S590000

Reexamination Certificate

active

06331362

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to:
refractory composite materials protected against oxidation at high temperature;
precursors or intermediate substances for preparing said materials; and
preparing said materials (by preparing said precursors), and preparing said precursors.
More precisely, the present invention relates to providing protection at high temperature (up to 1500° C. to 1600° C.) in an oxidizing atmosphere for highly refractory ceramic matrix composite materials that are reinforced by fibers that are known for being sensitive to oxygen at low temperature (below 900° C.); said composite materials being made via a solid process.
A solid process is a third process, distinct from the liquid process or the gas process, suitable for making composite materials. It is familiar to the person skilled in the art and generally comprises the following three steps:
a first step of preparing a slip (precursor of the matrix in the final product): suitable inorganic powders (Si
3
N
4
, SiC, . . . ) and appropriate additives (densification additives such as Al
2
O
3
and Y
2
O
3
, dispersants, and/or wetting agents, . . . ) are put into suspension in water;
a second step of incorporating fibers (reinforcing fibers) in said slip and of consolidating the whole (shaping by filtering under pressure): at the end of this step, the objective is to obtain a raw product of a density that is as high as possible; and
a third step of densification: this comprises sintering the raw product, which may be performed at a temperature higher than 1600° C., under load (a mechanical pressure is generated, e.g. 27 MPa), in an inert atmosphere or under inert gas pressure (the pressure imposed generally lies in the range 10 bars to 100 bars); in one or other of said contexts the inert gas used generally consists in nitrogen or argon; argon being recommended for use with silicon carbide.
A variant of that solid process is described in patent application CA-A-2 145 706.
DESCRIPTION OF THE RELATED ART
Prior art composite materials of the kind to which the present invention relates, i.e. composite materials made using the solid process and of the type recalled above [having a highly refractory ceramic matrix (e.g. a matrix of SiC, Si
3
N
4
, or SiAlON) reinforced by fibers that are sensitive to oxygen, such as long carbon fibers or long ceramic fibers (e.g. of the SiC, Si
3
N
4
, Al
2
O
3
type) precoated with an interphase of pyrolytic carbon or of boron nitride], have mechanical properties that are remarkable, making them suitable for numerous fields of application in the automobile, aviation, and aerospace industries, in particular. Nevertheless, insofar as said materials have poor resistance to being oxidized, their field of application has been limited, in particular to low temperatures.
SUMMARY OF THE INVENTION
The inventors have therefore been confronted with the technical problem of improving the resistance of such materials to being oxidized. To solve said problem, the inventors have devised an original form of external protection for said materials, that is capable of providing complete sealing against oxidizing gases, thereby enabling such materials to be used in an oxidizing atmosphere, in a temperature range extending from 500° C. to 1600° C.
According to the present invention, an original solution is proposed to the technical problem of protecting composite materials of the above type against oxidation at high temperature.
In general, the technical problem of providing composite materials with protection against being oxidized has already been investigated in depth.
In particular, it is known to provide such protection by depositing on said materials elements which constitute a glass or which are suitable for constituting a glass, e.g. after being oxidized. Said glass behaves in viscous manner at the temperatures at which the materials are used and therefore present healing properties. Nevertheless, that type of protection, which is implemented in particular on C/C type composite materials, is no longer effective at temperatures in excess of 1000° C.
To provide effective high temperature protection, proposals have also been made to deposit carbide or nitride coatings on the surface of composite materials by vapor deposition. That solution is not entirely satisfactory since high stresses are generated within said coated materials when they are raised to high temperature insofar as their structure no longer presents a uniform coefficient of thermal expansion.
Finally, according to application EP-A-483 009, it has been recommended to protect composite materials by forming a continuous phase within their matrices or at the surfaces thereof, which continuous phase is constituted by a ternary system of the Si—B—C type; said continuous phase is formed by chemical infiltration or by chemical vapor deposition starting from a gaseous phase. Like the previous technique, that technique is relatively cumbersome and expensive to implement.
The oxidizing mechanisms that take place within a monolithic ceramic raised to high temperature in an oxidizing atmosphere have also been described (more precisely the mechanisms that take place within the inter-grain phase of such a ceramic). Said mechanisms lead to a protective layer being formed that has a parabolic growth relationship, and that constitutes a diffusion barrier against oxygen.
A priori, the idea of taking advantage of such oxidizing mechanisms in the context of composite materials for the purpose of generating a protective layer in similar manner would have to be set aside insofar as any oxidation permanently damages the fibers present in the matrix of said composite materials. Nevertheless, it is on the basis of this idea that the inventors have developed the present invention in non-obvious manner.


REFERENCES:
patent: 3811928 (1974-05-01), Henney et al.
patent: 4093771 (1978-06-01), Goldstein et al.
patent: 4143182 (1979-03-01), Henney et al.
patent: 4457958 (1984-07-01), Lange et al.
patent: 4863773 (1989-09-01), Rousseau et al.
patent: 4976899 (1990-12-01), Rousseau et al.

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