Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1996-03-25
1998-04-14
Ryan, Patrick
Stock material or miscellaneous articles
Composite
Of inorganic material
428367, 428368, 428688, 428689, 442 59, 501 95, 427585, 427589, 427590, B32B 900
Patent
active
057389519
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to manufacturing composite materials comprising fiber reinforcement densified by means of a matrix, and having a lamellar interphase between the reinforcing fibers and the matrix.
A particular field of application of the invention is that of thermostructural composite materials. Such materials are characterized by mechanical properties that make them suitable for constituting structural elements, and by the ability to retain their mechanical properties up to high temperatures. Thermostructural composite materials are used, in particular, for making parts of engines or of reactors, or for making structural elements of space vehicles which are exposed to severe heating.
BACKGROUND OF THE INVENTION
Examples of thermostructural composite materials include carbon/carbon (C/C) composites comprising carbon fiber reinforcement and a carbon matrix, and ceramic matrix composites (CMC) comprising refractory (carbon or ceramic) fiber reinforcement and a ceramic matrix. Common CMCs are C/SiC composites (carbon fiber reinforcement and a silicon carbide matrix) and SiC/SiC composites (reinforcing fibers based on silicon carbide, and a silicon carbide matrix).
Composite materials in which the reinforcement is constituted by long fibers are known to possess greater toughness and greater mechanical strength than the corresponding monolithic materials.
In the case of thermostructural composites, it is also known that greater toughness is obtained by interposing an interphase between the fibers and the matrix, the interphase serving to transfer load from the matrix to the fibers while simultaneously deflecting cracks that appear in the matrix when the material is subjected to mechanical stress, thereby ensuring that the cracks do not propagate to the fibers, and simultaneously relieving residual stresses at the bottoms of the cracks.
To achieve these objects, the Applicants' document EP-A-0 172 082 proposes forming an interphase on the reinforcing fibers prior to densification of the matrix, the microtexture of the interphase being lamellar. That is achieved by forming on the fibers a layer of pyrolytic carbon (PyC) of the rough laminar type, or a layer of boron nitride (BN) obtained by chemical vapor infiltration or deposition. The stacks of sheets of atoms of PyC or of BN impart the lamellar microtexture to the interphase. In the resulting final material, when a crack reaches the interphase after propagating through the matrix, its mode of propagation is modified so that the crack is deflected parallel to the sheets of atoms in the interphase, i.e. parallel to the fiber, thereby protecting the fiber. In addition, because of its elastic nature in shear, the PyC or BN lamellar interphase serves to relieve the stresses at the bottom of the crack. By preserving the fibers in the cracked material, the material conserves its integrity and its mechanical properties, and consequently it presents much greater toughness than the same matrix material when it is monolithic.
It is well known that the microtexture of a PyC obtained by chemical vapor infiltration or deposition depends on infiltration or deposition conditions, and in particular on temperature and pressure. Thus, depending on conditions, it is possible to obtain PyCs that are highly anisotropic (lamellar microtexture), such as PyC of the rough laminar type, or PyCs that are not very anisotropic, (non-lamellar microtexture), such as PyC of the smooth laminar type. Unfortunately, during deposition of a PyC interphase whose thickness is typically greater than one hundred nanometers, it has been observed that the microtexture of the PyC can vary within the interphase, going from the rough laminar type to the smooth laminar type, and that this can happen without deposition conditions changing. Such uncontrolled variation means that the interphase no longer has optimum microtexture, with the main consequence of the mechanical properties of the composite material being less good than could have been expected from the reinfor
REFERENCES:
patent: 5354602 (1994-10-01), Stranford et al.
Dupel Pascal
Goujard Stephane
Heurtevent Fabrice
Pailler Rene
Gray J. M.
Ryan Patrick
Societe Europeene de Propulsion
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