Integral abradable seals
Devices, systems and methods for fabricating improved ceramic composite turbine shrouds with abradable seals are disclosed. A high temperature seal with an abradable coating is provided. The seal comprises a three-dimensional, high-density woven composite base structure recessed below the abradable coating, with loops incorporated in and protruding from the base structure. The abradable coating is integrally attached to the base structure via the loops. Additionally, a graded density seal is provided with a three-dimensional, low-density woven composite structure. The low-density structure is abradable. A three-dimensional, high-density woven composite base structure is recessed below the low-density structure, with the low-density structure integrally attached to the base structure via weaving.
1. A high temperature seal, comprising:
an abradable surface; and
a three-dimensional woven composite base structure recessed below said abradable surface, said woven composite base structure produced with a fiber preform, at least some of said preform's weave fibers extending from said base structure and over said abradable surface so as to anchor said abradable surface to said base structure.
2. The seal of claim 1 , wherein said abradable surface is porous.
3. The seal of claim 2 , wherein said abradable surface is reinforced with discontinuous ceramic fibers.
4. The seal of claim 3 , wherein said discontinuous ceramic fibers will be inserted beneath said weave fibers extending from said base structure and over said abradable surface, such that said discontinuous ceramic fibers are directly in contact with said base structure, thereby forming a fiber-reinforced assembly.
5. The seal of claim 4 , wherein said fiber-reinforced assembly is infiltrated with a ceramic-yielding solution to enhance strength.
6. The seal of claim 5 , wherein said ceramic-yielding solution forms a rare earth phosphate upon heat treatment.
7. The seal of claim 1 , wherein ceramic particles and/or porosity are added to said abradable surface to control the hardness and/or cutting properties of said abradable surface.
8. The seal of claim 1 , wherein said base structure acts as a support for said abradable surface.
9. The seal of claim 1 , wherein said seal is resistant to delamination and spallation.
10. The seal of claim 1 , wherein said base structure comprises a composite produced with an orthogonal weave fiber preform.
11. The seal of claim 1 , wherein said base structure comprises a ceramic matrix composite (CMC).
12. The seal of claim 1 , wherein said abradable surface comprises ceramic.
13. The seal of claim 1 , wherein the thermal expansion characteristics of said abradable surface and said base structure are closely matched.
14. The seal of claim 1 , wherein said seal is incorporated in shrouds for turbine engines.
15. The seal of claim 14 , wherein said seal maintains a close tolerance with the rotating blades of said turbine engines.