Method for processing ceramic fibers

1. A method of treating ceramic fibers based on metal carbide, the method comprising performing a first reagent gas heat treatment with at least one first reagent gas of the halogen type that chemically transforms the surface of the fiber to obtain a surface layer constituted mainly of carbon, and performing a second reagent gas heat treatment with at least one second reagent gas that eliminates the surface layer formed during the chemical transformation, wherein the treated fibers are Si—C—O fibers.

2. A method according to claim 1 , wherein the first reagent gas is selected from at least: dichlorine, difluorine, and hydrogen chloride.

3. A method according to claim 1 , wherein the surface layer formed during the first heat treatment presents thickness lying in the range 10 nm to 2 μm.

4. A method according to claim 1 , wherein the ceramic fibers are fibers based on silicon carbide.

5. A method according to claim 1 , wherein the first and second heat treatments are performed at the temperatures lower than the thermal stability temperature of the ceramic fibers.

6. A method according to claim 1 , wherein the first and second heat treatments are performed at atmospheric pressure.

7. A method according to claim 1 , wherein, after said first and second reagent gas heat treatments, the ceramic fibers present a mean breaking stress at ambient temperature that is more than 25% greater than that presented before said treatments.

8. A method according to claim 1 , wherein, after said first and second reagent gas heat treatments, the ceramic fibers present a static fatigue mean lifetime in air that is more than 10 times that presented before said treatments.

9. A method of fabricating a fiber preform comprising forming a fiber structure from ceramic fibers based on metallic carbide and being Si—C—O fibers, wherein the fibers are treated in accordance with the treatment method according to claim 1 .

10. A method according to claim 9 , wherein the fibers are treated before forming the fiber structure.

11. A method according to claim 9 , wherein the fibers are treated after forming the fiber structure.

12. A method of fabricating a fiber preform comprising forming a fiber structure from ceramic fibers based on metallic carbide, wherein the fibers are treated in accordance with a method comprising:

performing a first reagent gas heat treatment with at least one first reagent gas of the halogen type that chemically transforms the surface of the fiber to obtain a surface layer constituted mainly of carbon;

performing a second reagent gas heat treatment with at least one second reagent gas that eliminates the surface layer formed during the chemical transformation; and

performing a third reagent gas heat treatment on the fiber structure by using at least one reagent gas of the halogen type so as to form on the fibers of said fiber structure a surface layer constituted mainly of porous carbon, and forming a layer of pyrolytic carbon on said fibers.

13. A method according to claim 12 , wherein the surface layer of porous carbon presents thickness lying in the range 2 nm to 500 nm.

14. A method of fabricating a composite material part, the method comprising making a fiber preform in accordance with the method of claim 9 , and densifying said preform.

15. A method according to claim 1 , wherein the first and second heat treatments are performed at temperatures below 700° C.

16. A method according to claim 1 , wherein the fibers are treated in an enclosure having reagent gas inlets, the fibers in the enclosure being swept with the first and second reagent gases in succession, the enclosure also having an exhaust duct for eliminating gaseous effluents given off during the chemical reactions.