Composite materials and methods for making the same

Abstract

The present invention generally relates to mechanisms for preventing undesirable oxidation (i.e., oxidation protection mechanisms) 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. The getterer material(s) may form at least one compound which acts as a passivation layer, and/or is able to move by bulk transport (e.g., by viscous flow as a glassy material) to a crack, and sealing the crack, 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 super-imposed coatings thereon, at least one of which coatings may function as or contain an oxidation protection mechanism. Specifically, a coating comprising boron nitride which has been engineered or modified to contain some silicon exhibits improved corrosion resistance, specifically to oxygen and moisture. The coated materials may be useful as reinforcing materials in high performance 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.

What is claimed is:  
     
         1 . A reinforcement for a composite material, comprising: 
 (a) a permeable mass or preform comprising a plurality of bodies of at least one filler material; and    (b) a layer covering at least the majority of surface area presented by said bodies of filler material, said layer comprising boron, silicon and nitrogen.    
     
     
         2 . A composite material, comprising: 
 (a) a permeable mass or preform comprising a plurality of bodies of at least one filler material;    (b) a matrix embedding said permeable mass or preform; and    (c) at least one coating disposed between said bodies of at least one filler material and said matrix, at least one of said at least onecoating comprising boron, silicon and nitrogen.    
     
     
         3 . A method for making a reinforcement for a composite material, comprising: 
 providing at least one filler material;    communicating a local atmosphere comprising a halogenated boron source, a halogenated silicon source, and ammonia, to said at least one filler material; and    heating said at least one filler material and said local atmosphere to a temperature in the range of about 700° C. to 1200° C., thereby depositing on said at least one filler material a coating comprising boron, silicon and nitrogen.    
     
     
         4 . A coated fiber comprising a substrate fiber or filament and a plurality of coatings disposed coextensively with said substrate, said plurality comprising at least one protective coating and at least one debond coating disposed between said substrate and said at least one protective coating, and further at least one of said at least one debond coating comprises boron, silicon and nitrogen.  
     
     
         5 . A coated filler material for use as a reinforcement in a composite body, said coated filler comprising: 
 a substrate body; and    a layer no greater than about 0.5 micron in thickness covering at least a majority of surface presented by said substrate body, said layer comprising boron, silicon, nitrogen and oxygen.    
     
     
         6 . The reinforcement of  claim 1 , wherein said layer comprises boron nitride.  
     
     
         7 . The reinforcement of  claim 1 , wherein at least one of said plurality of bodies of at least one filler material comprises a filament or fiber, said layer being coextensive with a longitudinal axis of said filament or fiber.  
     
     
         8 . The coated fiber of  claim 4 , wherein said at least one protective coating comprises at least one material selected from the group consisting of silicon carbide, silicon nitride, and aluminum oxide.  
     
     
         9 . The coated fiber of  claim 4 , wherein said debond coating comprises boron nitride.  
     
     
         10 . The coated fiber of  claim 9 , wherein said debond coating is at least partially amorphous.  
     
     
         11 . The coated fiber of  claim 4 , wherein said debond coating exhibis limited crystallinity.  
     
     
         12 . The coated fiber of  claim 4 , wherein said debond coating comprises a plurality of regions or domains each about 5 to 20 nanometers in size, wherein the debond coating material within a region or domain exhibits a lamellar structure.  
     
     
         13 . The coated fiber of claim  30 , wherein a lamellar crystal structure within a given region or domain essentially is randomized in orientation with respect to a lamellar crystal structure in a different region or domain.  
     
     
         14 . The composite material of  claim 2 , further comprising at least one oxide glass network-former.  
     
     
         15 . The composite material of  claim 2 , wherein said matrix comprises a material selected from the group consisting of silicon, silicon carbide and aluminum oxide.  
     
     
         16 . The composite material of  claim 2 , further comprising at least one oxygen getterer.  
     
     
         17 . The composite material of  claim 2 , further comprising at least two zonal junctions, at least one of said zonal junctions being weak relative to the remaining zonal junction(s) to permit debonding and pull-out of said at least one filler material with respect to said matrix upon application of stress sufficient to cause fracture of said composite material.  
     
     
         18 . The composite material of  claim 17 , wherein said debonding occurs at an interface between a coating and (a) said matrix, (b) said filler material or (c) another coating, and not within a coating.  
     
     
         19 . The composite material of  claim 2 , wherein said matrix is produced by a method selected from the group consisting of directed metal oxidation and melt infiltration.  
     
     
         20 . The method of  claim 3 , wherein said halogenated boron source comprises boron trichloride, and said halogenated silicon source comprises silicon tetrachloride.  
     
     
         21 . The method of  claim 3 , wherein said local atmosphere is communicated to said at least one filler material at a pressure of about 1 Torr to about 10 Torr, and said temperature is in the range of about 700° C. to 800° C.  
     
     
         22 . The method of  claim 3 , wherein an atomic ratio of said halogenated silicon source to said halogenated boron source in said local atmosphere ranges from about 0.25 to about 7.7.  
     
     
         23 . The coated filler material of  claim 5 , wherein at least about 0.5 atom percent of said layer comprises said silicon.  
     
     
         24 . The coated filler material of  claim 5 , wherein said layer further comprises carbon.  
     
     
         25 . The coated filler material of  claim 5 , wherein said substrate body comprises a fiber comprising silicon carbide.  
     
     
         26 . The coated filler material of  claim 5 , wherein about 1 percent to about 3 percent of atoms making up said layer comprise silicon atoms.