Thermostructural composite structure with a compositional gradient, its manufacturing process
View Patent ↗Thermostructural composite structure having a compositional gradient, formed from a porous core ( 5 ) made of a refractory having a pore volume content of greater than or equal to 80%. The core ( 5 ) lies between two intermediate layers ( 6 a, 6 b ) comprising the carbon fiber reinforcement, densified by a matrix composed of the carbon phase and of a ceramic phase, and a refractory solid filler. Two monolithic ceramic shells ( 7 a, 7 b ) cover the intermediate layers in order to give stiffness to the entire structure.
1. A process for manufacturing a laminated thermostructural composite structure having a compositional gradient, comprising the following steps:
a) machining of a preform in a porous refractory component, the preform having a pore volume content of greater than or equal to 80%;
b) application of a liquid composition, containing a ceramic precursor polymer and a refractory solid filler, to all the accessible surfaces of the preform, crosslinking of the polymer and conversion of the crosslinked polymer into a ceramic by heat treatment in order to form an intermediate layer and to reduce the porosity at the surface of the preform; and
c) formation of a ceramic coating on the immediate layer, said ceramic coating being deposited by chemical vapor infiltration so as to form a ceramic shell over all the external surfaces of the preform.
2. The process as claimed in claim 1 , wherein the preform is formed from a reinforcement of carbon fibers of an ex-rayon type, consolidated by a carbon matrix.
3. The process as claimed in claim 1 , wherein step a) of machining the preform includes the hollowing-out of cavities in the porous refractory component in order to form stiffeners.
4. The process as claimed in claim 3 , wherein the step of machining the preform furthermore includes the formation of a substantially plane surface, said surface being polished after the chemical vapor infiltration step in order to form an optical surface.
5. The process as claimed in claim 1 , wherein the liquid composition includes a solvent for the ceramic precursor polymer.
6. The process as claimed in claim 1 , wherein the solid filler comprises at least one refractory powder whose mean particle size is less than 100 microns.
7. The process as claimed in claim 6 , wherein the mean particle size of the powder is between 5 microns and 50 microns.
8. The process as claimed in claim 1 , wherein the solid filler comprises at least two powders of different mean particle sizes.
9. The process as claimed in claim 1 , wherein the chemical vapor infiltration is carried out at a constant temperature.
10. The process as claimed in claim 1 , wherein the coating formed by chemical vapor infiltration is of silicon carbide.
11. The process as claimed in claim 2 , wherein:
step a) of machining the preform includes the hollowing-out of cavities in the porous refractory component in order to form stiffeners;
the step of machining the preform furthermore includes the formation of a substantially plane surface, said surface being polished after the chemical vapor infiltration step in order to form an optical surface;
the liquid composition includes a solvent for the ceramic precursor polymer;
the solid filler comprises at least one refractory powder whose mean particle size is less than 100 microns;
the mean particle size of the powder is between 5 microns and 50 microns;
the solid filler comprises at least two powders of different mean particle sizes;
the chemical vapor infiltration is carried out at a constant temperature;
the coating formed by chemical vapor infiltration is of silicon carbide.