Composite materials and methods for making the same

Details Composite materials and methods for making the same Composite materials and methods for making the same

1994-09-30

1996-12-17

Ryan, Patrick J.

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

428361, 428366, 428368, 428375, 428378, 428384, 428403, 428404, 428288, 428297, 428325, 427214, 427215, 4274191, 501 95, B32B 700, C04B 3502, B05D 136

Patent

active

055851657

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention generally relates to mechanisms for preventing undesirable oxidation (i.e., oxidation protection mechanisms) of reinforcement materials in composite bodies. The oxidation protection mechanisms include getterer materials which are added to the composite body which gather or scavenge undesirable oxidants which may enter the composite body. The getterer materials may be placed into at least a portion of the composite body such that any undesirable oxidant approaching, for example, a fiber reinforcement, would be scavenged by (e.g., reacted with) the getterer. In a preferred embodiment of the present invention, the getterer material(s) form at least one compound (e.g., at least one glassy material) which acts as a crack sealant, thereby further enhancing the oxidation protection of the composite body. One or more ceramic filler materials which serve as reinforcements may have a plurality of superimposed coatings thereon, at least one of which coatings may function as a getterer. The coated materials may be useful as reinforcing materials in ceramic matrix composites to provide improved mechanical properties such as fracture toughness. The present invention also relates to improved composites which incorporate these materials, and to their methods of manufacture.


BACKGROUND ART

A ceramic composite is a heterogeneous material or article comprising a ceramic matrix and filler such as ceramic particles, fibers or whiskers, which are intimately combined to achieve desired properties. These composites are produced by such conventional methods as hot pressing, cold pressing and firing, hot isostatic pressing, and the like. However, these composites typically do not exhibit a sufficiently high fracture toughness to allow for use in very high stress environments such as those encountered by gas turbine engine blades.
A novel and useful method for producing self-supporting ceramic composites by the directed oxidation of a molten precursor metal is disclosed in Commonly Owned U.S. Pat. No. 4,851,375, which issued on Jul. 25, 1989, described below in greater detail. However, the processing environment is relatively severe, and there is a need, therefore, to protect certain fillers from the strong oxidation environment. Also, certain fillers may be reduced at least partially by molten metal, and therefore, it may be desirable to protect the filler from this local reducing environment. Further, the protective means should be conducive to the metal oxidation process, yet not degrade the properties of the resulting composite, and even more desirably provide enhancement to the properties. Still further, in some instances it may be desirable for the means or mechanisms for protecting the filler during matrix or composite formation to also protect the fillers against undesirable attack of oxidants diffusing through the matrix during actual service of the composite.
It is known in the art that certain types of ceramic fillers serve as reinforcing materials for ceramic composites, and the selection or choice of fillers can influence the mechanical properties of the composite. For example, the fracture toughness of the composite can be increased by incorporating certain high strength filler materials, such as fibers or whiskers, into the ceramic matrix. When a fracture initiates in the matrix, the filler at least partially debonds from the matrix and spans the fracture, thereby resisting or impeding the progress of the fracture through the matrix. Upon the application of additional stress, the fracture propagates through the matrix, and the filler begins to fracture in a plane different from that of the matrix, pulling out of the matrix and absorbing energy in the process. Pull-out is believed to increase certain mechanical properties such as work-of-fracture by releasing the stored elastic strain energy in a controlled manner through friction generated between the material and the surrounding matrix.
Debonding and pull-out have been achieved in the prior art by applying a suitable coating

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