Silicon carbide bodies having high toughness and fracture resistance and method of making same

Claim 2

A process for producing a sintered silicon carbide ceramic body having superior fracture toughness comprising: a) forming a homogeneous mixture comprising: 1) one or more nitrogen containing aluminum compounds in an overall amount of from 0.5 weight percent to about 15 weight percent, based upon the total wight of the mixture; 2) one or more rare earth oxides in an overall amount of from about 0.1 weight percent and 15 weight percent, based upon the weight of the mixture; 3) silicon carbide, in an amount of from about 70 weight percent to about 99.4 weight percent, based on the weight of the mixture, and having a specific surface area of from about 1 to about 100 square meters per gram; wherein said mixture includes more than 0.01 weight percent, to about 10 weight percent, of either non-crystalline reactive oxygen from the surface of said silicon carbide or reactive oxygen in any form from said one or more nitrogen containing compound and/or from said one or more rare earth oxides, or both said reactive oxygen being in elemental or in a compound or both; b) combining said mixture with a temporary binder; c) forming the mixture and binder in such a way as to produce a shaped object; and d) firing the shaped mixture under such conditions of time and temperature in an atmosphere inert to silicon carbide or in a vacuum at a temperature of between about 1775° C. and about 2200° C. until a sintered ceramic body having a predominantly homogeneous, predominantly equiaxed and predominantly fine-grain microstructure is formed having a fracture toughness, as measured by the single edge notched beam test, of at least 7 MPam 1/2 .

Claim 3

The process according to claim 1 wherein said fracture toughness is at least 8 MPam 1/2 .

Claim 4

The process according to claim 1 wherein said fracture toughness is at least 9 MPam 1/2 .

Claim 5

The process according to claim 1 when said shaped object is fired in an argon atmosphere.

Claim 6

A process according to claim 1 when the silicon carbide of said mixture is predominantly alpha, non-cubic crystalline silicon carbide.

Claim 7

A process according to claim 1 when the silicon carbide of the sintered composite body is predominantly alpha, non-cubic crystalline silicon carbide.

Claim 8

A process according to claim 1 wherein said mixture further includes a lubricant.

Claim 9

A process according to claim 1 wherein said sintered body has achieved at least about 95 percent of theoretical density.

Claim 10

A process according to claim 1 wherein said sintered body has achieved at least about 98 percent of theoretical density.

Claim 11

The process according to claim 1 wherein said one or more nitrogen containing aluminum compounds are in an overall amount of from 0.5 weight percent to 10 weight percent.

Claim 12

The process according to claim 1 wherein said one or more rare earth oxides are in an overall amount of from 0.1 weight percent to 8.0 weight percent.

Claim 13

The process according to claim 1 wherein said one or more nitrogen containing aluminum compounds are in an overall amount of from 1.5 weight percent to 10 weight percent.

Claim 14

The process according to claim 1 wherein said one or more rare earth oxides are in an amount of from 0.25 weight percent to 8.0 weight percent.

Claim 15

The process according to claim 1 wherein the molar ratio, of said one or more nitrogen containing aluminum compounds to said one or more rare earth oxides, is between 3 and 55.

Claim 16

The process according to claim 1 wherein the molar ratio, of said one or more nitrogen containing aluminum compounds to said one or more rare earth oxides, is between 3 and 21.

Claim 17

The process according to claim 1 wherein the molar ratio, of said one or more nitrogen containing aluminum compounds to said rare earth oxides, is between 3.4 and 9.2.

Claim 18

A process according to claim 1 wherein said sintered body is subject to a further HIPing treatment under gas pressure at about 2000° C. for a period of about 0.5 hour.

Claim 19

A process according to claim 1 wherein said homogeneous mixture is combined by vibratory milling said components for about 4 hours.

Claim 20

A process according to claim 1 wherein said homogeneous mixture is combined using distilled water.

Claim 21

A process according to claim 1 wherein said homogeneous mixture is combined using heptane.

Claim 22

A process according to claim 1 wherein said homogeneous mixture is combined by ball milling.

Claim 23

A process according to claim 1 wherein said homogeneous mixture is combined by attrition milling.

Claim 24

A process according to claim 1 wherein said mixture is spray dried before being formed to produce a shaped object.

Claim 25

A process according to claim 1 wherein said one or more nitrogen containing aluminum compounds are selected from the group consisting of aluminum nitride, aluminum oxynitride, aluminum carbonitride and/or aluminum oxynitride spinel.

Claim 26

A process according to claim 1 wherein said one or more nitrogen containing aluminum compounds comprises aluminum nitride.

Claim 27

A process according to claim 1 wherein said reactive oxygen is surface oxygen from the surface of said silicon carbide and is present in an amount of up to 8.0 weight percent upon the weight of the silicon carbide.

Claim 28

A process according to claim 1 wherein said reactive oxygen is surface oxygen from the surface of said silicon carbide and is present in an amount of up to 4.0 weight percentbased upon the weight of the silicon carbide.

Claim 29

A sintered silicon carbide ceramic body derived from a uniform mixture comprising from about 70 weight percent to about 99.6 weight percent of silicon carbide, from about 0.5 weight percent to about 15 weight percent overall of one or more nitrogen containing aluminum compounds, and from about 0.1 weight percent to about 15 weight percent overall of one or more rare earth oxides, all based upon the weight of the mixture, wherein said sintered ceramic body has a density of 2.9 g/cm 3 or greater, a fracture toughness, as measured by the single edge notched beam test, of at least 7 MPam 1/2 , has a predominantly equiaxed, predominantly homogeneous and predominantly fine-grain microstructure with a discontinuous crystalline second phase located predominantly at the triple points of silicon carbide grains.

Claim 30

A sintered silicon carbide ceramic body derived from a uniform mixture comprising from about 70 weight percent to about 99.6 weight percent of silicon carbide, from about 0.5 weight percent to about 15 weight percent overall of one or more nitrogen containing aluminum compounds, and from about 0.1 weight percent to about 15 weight percent overall of one or more rare earth oxides, all based upon the weight of the mixture, wherein said sintered ceramic body has a density of 2.9 g/cm 3 or greater, a fracture toughness, as measured by the single edge notched beam test, of at least 7 MPam 1/2 , has a predominantly equiaxed, predominantly homogeneous and predominantly fine-grain microstructure with a discontinuous crystalline second phase located predominantly at the triple points of silicon carbide grains.

Claim 31

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said fracture toughness is at least 8 MPam 1/2 .

Claim 32

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said fracture toughness is at least 9 MPam 1/2 .

Claim 33

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said one or more nitrogen containing aluminum compounds are selected from the group consisting of aluminum nitride, aluminum oxynitride, aluminum carbonitride, and/or aluminum oxynitride spinel.

Claim 34

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said one or more nitrogen containing aluminum compounds are aluminum nitride.

Claim 35

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said one or more nitrogen containing aluminum compounds are in an overall amount of from 1.5 weight percent to 10 weight percent.

Claim 36

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said one or more rare earth oxides are in an overall amount of from 0.1 weight percent to 8.0 weight percent.

Claim 37

A sintered silicon carbide ceramic body in accordance with claim 28 wherein said body has a room temperature electrical resistivity of less than 1000 ohm cm.

Claim 38

A sintered silicon carbide ceramic body in accordance with claim 28 having a microstructure which exhibits predominantly clean grain boundaries between adjacent grains of silicon carbide.

Claim 39

A sintered silicon carbide ceramic body having a predominantly fine-grain, predominantly equiaxed and predominantly homogeneous microstructure which, when fractured, exhibits a predominantly intergranular fracture mode and a fracture toughness of at least 7 MPam 1/2 .

Claim 40

A sintered silicon carbide ceramic body having a predominantly fine-grain, predominantly equiaxed and predominantly homogeneous microstructure which, when fractured, exhibits a predominantly intergranular fracture mode and a fracture toughness of at least 7 MPam 1/2 .

Claim 41

A sintered silicon carbide ceramic body having a microstructure which exhibits predominantly clean grain boundaries between adjacent grains of silicon carbide, with the remaining grain boundaries having a discontinuous second phase located predominantly at the triple points of adjacent grains of silicon carbide, having a predominantly fine-grain, predominantly equiaxed and predominantly homogeneous microstructure and which, when fractured, exhibits a predominantly intergranular fracture mode and a fracture toughness of at least 7 MPam 1/2 .

Claim 42

A sintered silicon carbide ceramic body having a microstructure which exhibits predominantly clean grain boundaries between adjacent grains of silicon carbide, with the remaining grain boundaries having a discontinuous second phase located predominantly at the triple points of adjacent grains of silicon carbide, having a predominantly fine-grain, predominantly equiaxed and predominantly homogeneous microstructure and which, when fractured, exhibits a predominantly intergranular fracture mode and a fracture toughness of at least 7 MPam 1/2 .

Claim 43

A sintered silicon carbide ceramic body made from a uniform mixture comprising from about 95.5 weight percent of silicon carbide, about 2.5 weight percent of aluminum nitride, and about 2.0 percent by weight of yttrium oxide, all percentages based upon the total mixture, wherein said sintered ceramic body has a density greater than 95 percent of theoretical, a fracture toughness, as measured by the single edge notched beam test, of at least 9 MPam 1/2 and a predominantly equiaxed, predominantly fine-grain and predominantly homogeneous microstructure.

Claim 44

A sintered silicon carbide ceramic body made from a uniform mixture comprising from about 95.5 weight percent of silicon carbide, about 2.5 weight percent of aluminum nitride, and about 2.0 percent by weight of yttrium oxide, all percentages based upon the total mixture, wherein said sintered ceramic body has a density greater than 95 percent of theoretical, a fracture toughness, as measured by the single edge notched beam test, of at least 9 MPam 1/2 and a predominantly equiaxed, predominantly fine-grain and predominantly homogeneous microstructure.

Claim 45

A sintered silicon carbide ceramic body made from a uniform mixture comprising about 97.25 weight percent of silicon carbide, about 2.5 weight percent of aluminum nitride, and about 0.25 weight percent of yttrium oxide, all percentages based upon the total mixture, wherein said sintered ceramic body has a density greater that 95 percent of theoretical, a fracture toughness, as measured by the single edge notched beam test, of at least 9 MPam 1/2 and a predominantly equiaxed, predominantly fine-grain and predominantly homogeneous microstructure.

Claim 46

A sintered silicon carbide ceramic body made from a uniform mixture comprising about 97.25 weight percent of silicon carbide, about 2.5 weight percent of aluminum nitride, and about 0.25 weight percent of yttrium oxide, all percentages based upon the total mixture, wherein said sintered ceramic body has a density greater that 95 percent of theoretical, a fracture toughness, as measured by the single edge notched beam test, of at least 9 MPam 1/2 and a predominantly equiaxed, predominantly fine-grain and predominantly homogeneous microstructure.

Claim 47

A process for producing a sintered silicon carbide ceramic body having superior fracture toughness comprising: a) forming a uniform mixture comprising: 1) one or more nitrogen containing aluminum compounds in an overall amount of from 1.5 weight percent to about 10 weight percent, based upon the total weight of the mixture; 2) one or more rare earth oxides in an overall amount of from about 0.25 weight percent and 8 weight percent, based upon the weight of the mixture; 3) silicon carbide, in an amount of from about 82 weight percent to about 98.75 weight percent, based on the weight of the mixture, and having a specific surface area of from about 1 to about 100 square meters per gram; wherein said mixture includes a range of about more than 0.3 weight percent to about 4 weight percent, of either non-crystalline reactive oxygen from the surface of said silicon carbide or reactive oxygen in any form from said one or more nitrogen containing compound and/or from said one or more rare earth oxides, or both, said reactive oxygen being in elemental or in a compound or both; b) combining said mixture with a temporary binder; c) forming the mixture and binder in such a way as to produce a shaped object; and d) firing the shaped mixture under such conditions of time and temperature in an atmosphere inert to silicon carbide or in a vacuum at a temperature of between about 1775° C. and about 2200° C. until a sintered ceramic body having a predominantly homogeneous, predominantly equiaxed and predominantly fine-grain microstructure is formed having a fracture toughness, as measured by the single edge notched beam test, of at least 7 MPam 1/2 .

Claim 48

A process for producing a sintered silicon carbide ceramic body having superior fracture toughness comprising: a) forming a uniform mixture comprising: 1) one or more nitrogen containing aluminum compounds in an overall amount of from 1.5 weight percent to about 10 weight percent, based upon the total weight of the mixture; 2) one or more rare earth oxides in an overall amount of from about 0.25 weight percent and 8 weight percent, based upon the weight of the mixture; 3) silicon carbide, in an amount of from about 82 weight percent to about 98.75 weight percent, based on the weight of the mixture, and having a specific surface area of from about 1 to about 100 square meters per gram; wherein said mixture includes a range of about more than 0.3 weight percent to about 4 weight percent, of either non-crystalline reactive oxygen from the surface of said silicon carbide or reactive oxygen in any form from said one or more nitrogen containing compound and/or from said one or more rare earth oxides, or both, said reactive oxygen being in elemental or in a compound or both; b) combining said mixture with a temporary binder; c) forming the mixture and binder in such a way as to produce a shaped object; and d) firing the shaped mixture under such conditions of time and temperature in an atmosphere inert to silicon carbide or in a vacuum at a temperature of between about 1775° C. and about 2200° C. until a sintered ceramic body having a predominantly homogeneous, predominantly equiaxed and predominantly fine-grain microstructure is formed having a fracture toughness, as measured by the single edge notched beam test, of at least 7 MPam 1/2 .

Claim 49

A sintered silicon carbide ceramic body comprised of a predominately equiaxed, predominately homogeneous and predominately fine-grain microstructure comprised of silicon carbide, aluminum, nitrogen and yttria, having a density of at least 90% of theoretical and exhibiting a fracture toughness of at least 7 MPam 1/2 .

Claim 50

A sintered silicon carbide ceramic body comprised of a predominately equiaxed, predominately homogeneous and predominately fine-grain microstructure comprised of silicon carbide, aluminum, nitrogen and yttria, having a density of at least 90% of theoretical and exhibiting a fracture toughness of at least 7 MPam 1/2 .

Claim 51

The ceramic body of claim 42, having a bend strength of at least 60 ksi based on a 4-point bend test.

Claim 52

The ceramic body of claim 42, having a errosion volume loss after ten minutes of exposure of about 0.001 cm 3 .

Claim 53

The ceramic body of claim 42, having an oxidation weight gain of about 0.1911 g/cm 2 at 1371° C. in 24 hours.

Claim 54

The ceramic body of claim 42, having a hardness of at least 21 GPa.

Claim 55

The ceramic body of claim 42, having an electrical resistivity of about 0.02-10,000 Ohm cm at room temperature.

Claim 56

The ceramic body of claim 42, having at least 10 19 atoms of nitrogen per cubic centimeter of silicon carbide.

Claim 57

A sintered silicon carbide ceramic body comprised of a predominately equiaxed, predominately homogenous and predominately fine-grain microstructure consisting essentially of silicon carbide, aluminum, nitrogen and yttria, having a density of at least 90% of theoretical, and exhibiting a fracture toughness of at least 7 MPam 1/2 .

Claim 58

A sintered silicon carbide ceramic body comprised of a predominately equiaxed, predominately homogenous and predominately fine-grain microstructure consisting essentially of silicon carbide, aluminum, nitrogen and yttria, having a density of at least 90% of theoretical, and exhibiting a fracture toughness of at least 7 MPam 1/2 .