Fibre-reinforced ceramic and process therefor

Claim 2

A composite ceramic material having a modulus of rupture of at least 550 MPa and a Young's modulus at strains below 300 MPa of at least 375 GPa, further characterized by non-catastrophic initial failure under stress, and comprising: (a) a reinforcing phase of silicon carbide filaments at least one millimeter in length disposed throughout the body of the material, and (b) a matrix of predominantly silicon nitride surrounding said reinforcing phase.

Claim 3

A composite according to claim 1, wherein said silicon carbide filaments are predominantly continuous from one edge of the composite to an opposite edge.

Claim 4

A composite according to claim 1 or 2, wherein said silicon carbide filaments are substantially straight and mutually parallel in most volume regions of the composite not greater than one millimeter in maximum dimension.

Claim 5

A composite according to any one of the preceding claims, wherein said silicon carbide filaments are formed by chemical vapor deposition onto a filamentous carbon substrate.

Claim 6

A process for the manufacture of ceramic composites, comprising the steps of: (a) forming an array of silicon carbide filaments at least one millimeter in length, said array filling a substantial fraction of the volume desired for the eventual composite; (b) impregnating said array of part (a) with a mixture of silicon powder and a non-siliceous organic polymer in solvent; (c) drying the impregnated array of filaments formed in part (b) to form a green composite; (d) debinderizing the dried impregnated array from part (c) by heating it to a temperature not greater than l250 o C. in an inert gas atmosphere for a sufficient time to convert the organic chemical content of the dried coated array into gaseous products and to expel substantially all of such gaseous products from the array; and (e) reaction bonding the debinderized array by heating it in a nitrogen atmosphere to a temperature below the melting point of silicon for a sufficient time to convert substantially all the elemental silicon in the array to silicon nitride.

Claim 7

A process for the manufacture of ceramic composites, comprising the steps of: (a) forming an array of silicon carbide filaments at least one millimeter in length, said array filling a substantial fraction of the volume desired for the eventual composite; (b) impregnating said array of part (a) with a mixture of silicon powder and a non-siliceous organic polymer in solvent; (c) drying the impregnated array of filaments formed in part (b) to form a green composite; (d) debinderizing the dried impregnated array from part (c) by heating it to a temperature not greater than l250 o C. in an inert gas atmosphere for a sufficient time to convert the organic chemical content of the dried coated array into gaseous products and to expel substantially all of such gaseous products from the array; and (e) reaction bonding the debinderized array by heating it in a nitrogen atmosphere to a temperature below the melting point of silicon for a sufficient time to convert substantially all the elemental silicon in the array to silicon nitride.

Claim 8

A process for the manufacture of an intermediate tape useful for the manufacture of ceramic composites, comprising the steps of: (a) forming a layer one filament thick of substantially straight and coparallel continuous silicon carbide filaments; (b) impregnating said layer of part (a) with a mixture of silicon powder and a non-siliceous organic polymer in solvent; and (c) drying the coated layer of filaments formed in part (b) to form a flexible coherent tape.

Claim 9

A process for the manufacture of an intermediate tape useful for the manufacture of ceramic composites, comprising the steps of: (a) forming a layer one filament thick of substantially straight and coparallel continuous silicon carbide filaments; (b) impregnating said layer of part (a) with a mixture of silicon powder and a non-siliceous organic polymer in solvent; and (c) drying the coated layer of filaments formed in part (b) to form a flexible coherent tape.

Claim 10

A process for the manufacture of ceramic composites, comprising the steps of: (a) segmenting a tape formed according to claim 6; (b) assembling the segments formed in part (a) into the approximate size and shape of the composite to be formed; (c) mechanically compressing the assembly formed in part (b) to give a coherent body with the final shape and size desired for the composite; (d) debinderizing the compressed assembly of part (c) by heating it to a temperature not greater than 1250°C. in an inert gas atmosphere for a sufficient time to convert the organic chemical content of the assembly into gaseous products and to expel substantially all of such gaseous products from the assembly; and (e) reaction bonding the debinderized assembly by heating it in a nitrogen atmosphere to a temperature below the melting point of silicon for a sufficient time to convert substantially all the elemental silicon in the assembly to silicon nitride.

Claim 11

A process according to claim 5 or 7, wherein the shape of the composite to be formed is a parallelepiped and the segments of tape are assembled in a stack with the orientation of filaments in all layers of the stack maintained mutually parallel.

Claim 12

A flexible tape useful as an intermediate for the manufacture of ceramic composites, comprising: (a) a closely packed layer one filament thick of substantially straight and coparallel continuous silicon carbide filaments constituting more than ten percent of the volume of the tape; and (b) a matrix of a mixture of silicon powder and a non-siliceous organic polymer impregnating said layer of part (a).

Claim 13

A flexible tape useful as an intermediate for the manufacture of ceramic composites, comprising: (a) a closely packed layer one filament thick of substantially straight and coparallel continuous silicon carbide filaments constituting more than ten percent of the volume of the tape; and (b) a matrix of a mixture of silicon powder and a non-siliceous organic polymer impregnating said layer of part (a).

Claim 14

A flexible tape according to claim 9, wherein said silicon carbide filaments are formed by vapor deposition of silicon carbide upon a carbonaceous filament substrate, said silicon carbide filaments have a carbon- rich surface layer, and said organic polymer consists essentially of poly(vinylbutyral) and plasticizers therefor.