Silicon carbide whisker reinforced ceramic composites and method for making same

Claim 2

A ceramic composite characterized by increased toughness and resistance to fracture, comprising a composite defined by a matrix of ceramic material, .Iadd.wherein said matrix is selected from the group consisting of A 2 O 3 , mullite and B 4 C .Iaddend.having homogeneously dispersed therein about 5 to 60 vol. % of silicon carbide whiskers, with said silicon carbide whiskers having a microcrystalline structure and .[.in.]. a size range of about 0.6 μm in diameter and a length of 10 to 80 μm .Iadd.and which are characterized by crack bridging pull-out from said matrix when said matrix is subjected to crack-forming stresses, .Iaddend.said composite being of a density greater than about 99% of the theoretical density.

Claim 3

The ceramic composite claimed in claim 1, wherein the silicon carbide whiskers are .[.essentially unidirectionally oriented.]. .Iadd.preferentially aligned and randomly distributed in planes .Iaddend.in the matrix.

Claim 4

The ceramic composite claimed in claim 2, wherein the matrix is Al 2 O 3 , the concentration of silicon carbide whiskers in the matrix is about 20 vol. %, wherein fracture toughness of the composite is in the range of about 8 to 9 MPa.m 1/2 at room temperature, and wherein fracture strength of the composite is in the range of about 590 to 899 MPa at room temperature.

Claim 5

The ceramic composite claimed in claim 2 wherein the matrix is 3Al 2 O 3 .2SiO 2 , the concentration of silicon carbide whiskers in the composite is about 20 vol. % wherein fracture toughness of the composition is 4.6 MPa.m 1/2 at room temperature, and wherein fracture strength of the composite is about 438 MPa at room temperature.

Claim 6

The ceramic composite claimed in claim 1, wherein the silicon carbide whiskers are essentially omnidirectionally oriented in the matrix. .[.6. The ceramic composite claimed in claim 1, wherein the ceramic matrix material is selected from the group consisting of Al 2 O 3 ,

Claim 7

3Al 2 O 3 .2SiO 2 , B 4 C..]. 7. A method for preparing a ceramic composite having increased toughness and resistance to fracture, comprising the steps of forming a homogeneous mixture of .[.particulate ceramic material with.]. about 5 to 60 vol. % of silicon carbide whiskers having a monocrystalline structure and .[.in.]. a size range of about 0.6 μm in diameter and a length of 10 to 80 μm .Iadd.with particulate matrix wherein said matrix is selected from the group consisting of Al 2 O 3 , mullite and B 4 C, .Iaddend.and hot pressing the mixture at a pressure in the range of about 28 to 70 MPa and temperature in the range of about 1600° to 1900° C. for a duration of 0.75 to 2.5 hours to provide a composite with a density greater than about 99% of the theoretical density of the ceramic material .Iadd.and in which composite the silicon carbide whiskers are characterized by crack bridging pull-out from the ceramic material when said composite is subjected to

Claim 8

3Al 2 O 3 .2SiO 2 , B 4 C..]. 7. A method for preparing a ceramic composite having increased toughness and resistance to fracture, comprising the steps of forming a homogeneous mixture of .[.particulate ceramic material with.]. about 5 to 60 vol. % of silicon carbide whiskers having a monocrystalline structure and .[.in.]. a size range of about 0.6 μm in diameter and a length of 10 to 80 μm .Iadd.with particulate matrix wherein said matrix is selected from the group consisting of Al 2 O 3 , mullite and B 4 C, .Iaddend.and hot pressing the mixture at a pressure in the range of about 28 to 70 MPa and temperature in the range of about 1600° to 1900° C. for a duration of 0.75 to 2.5 hours to provide a composite with a density greater than about 99% of the theoretical density of the ceramic material .Iadd.and in which composite the silicon carbide whiskers are characterized by crack bridging pull-out from the ceramic material when said composite is subjected to

Claim 9

crack-forming stresses..Iaddend. 8. A method for preparing a ceramic composite as claimed in claim 7, wherein the ceramic material is of a particle size less than about 44 m. .[.9. A method for preparing a cermamic composite as claimed in claim 8, wherein the ceramic material is selected from the group consisting of Al 2 O 3 , 3Al 2

Claim 10

O 3 .2SiO 2 , and B 4 C..]. 10. A method for preparing a ceramic composite as claimed in claim .[.9.]. .Iadd.7.Iaddend., wherein the silicon carbide whiskers are preferentially aligned along an axis of the composite by unidirectionally hot pressing the mixture along an axis

Claim 11

peripendicular to the first-mentioned axis. 11. The method for preparing a ceramic composite as claimed in claim .[.9.]. .Iadd.7.Iaddend., wherein the silicon carbide whiskers are omnidirectionally aligned with the composite by isostatically hot pressing the mixture.