Method of making reaction bonded/hot pressed Si3 N4 for use as a cutting tool

Claim 1

A method of making a reaction bonded, hot pressed silicon nitride comprising object having resistance to oxidation at high temperatures, comprising: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent and from 0.4 to 5.0 %. alumina, said oxynitride forming agent and alumina being present in amounts to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 and oxynitride cyrstallites, encapsulated by a glass film; (b) heating said compact in a nitriding atmosphere, without the use of pressure normally associated with hot pressing, to produce said converted compact, said converted compact having a size greater than and a density less than the final object to be formed; and (c) hot oppressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising object of required dimension and density useful for a cutting tool and consisting essentially of the chemistry in said converted compact.

Claim 2

A method of making a reaction bonded, hot pressed silicon nitride comprising object having resistance to oxidation at high temperatures, comprising: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent and from 0.4 to 5.0 %. alumina, said oxynitride forming agent and alumina being present in amounts to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 and oxynitride cyrstallites, encapsulated by a glass film; (b) heating said compact in a nitriding atmosphere, without the use of pressure normally associated with hot pressing, to produce said converted compact, said converted compact having a size greater than and a density less than the final object to be formed; and (c) hot oppressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising object of required dimension and density useful for a cutting tool and consisting essentially of the chemistry in said converted compact.

Claim 19

A method of making a reaction bonded, hot pressed silicon nitride comprising cutting tool which has increased oxidation resistance at 1000° C., comprising the steps of: (a) forming a compact from a mixture of silicon, SiO 2 , Y 2 O 3 and a glass forming oxide selected from the class consisting of the oxides of magnesium, iron, calcium and chromium reactive with SiO 2 and Y 2 O 3 to form upon heating a controlled amount of a protective amorphous silicate glass, said Y 2 O 3 being present in said mixture in an amount of 3-19% by weight of said silicon, said glass forming oxide being present in an amount of at least 0.4 and up to 1.0% by weight of said silicon, said SiO 2 being present in an amount of 1-3% by weight of said silicon, and said mixture having a Y 2 O 3 /SiO 2 ratio of 1:1-6:4; (b) heating said compact in a nitriding atmosphere, to product a silicon nitride comprising body consisting of Si 3 N 4 , at least one yttrium silicon oxynitride present in an amount of 3-15% by weight of said body and dispersed throughout, up to 0.5% free silicon and residual Y 2 O 3 , 1% or less silicate glass encapsulating said yttrium silicon oxynitride, at lease 60% of said Si 3 N 4 being in the alpha form, said body having a size greater than and a density less than said tool; (c) hot pressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising cutting tool of required dimension and density consisting essentially of the chemistry developed previously during said heating step.

Claim 20

A method of making a reaction bonded, hot pressed silicon nitride comprising cutting tool which has increased oxidation resistance at 1000° C., comprising the steps of: (a) forming a compact from a mixture of silicon, SiO 2 , Y 2 O 3 and a glass forming oxide selected from the class consisting of the oxides of magnesium, iron, calcium and chromium reactive with SiO 2 and Y 2 O 3 to form upon heating a controlled amount of a protective amorphous silicate glass, said Y 2 O 3 being present in said mixture in an amount of 3-19% by weight of said silicon, said glass forming oxide being present in an amount of at least 0.4 and up to 1.0% by weight of said silicon, said SiO 2 being present in an amount of 1-3% by weight of said silicon, and said mixture having a Y 2 O 3 /SiO 2 ratio of 1:1-6:4; (b) heating said compact in a nitriding atmosphere, to product a silicon nitride comprising body consisting of Si 3 N 4 , at least one yttrium silicon oxynitride present in an amount of 3-15% by weight of said body and dispersed throughout, up to 0.5% free silicon and residual Y 2 O 3 , 1% or less silicate glass encapsulating said yttrium silicon oxynitride, at lease 60% of said Si 3 N 4 being in the alpha form, said body having a size greater than and a density less than said tool; (c) hot pressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising cutting tool of required dimension and density consisting essentially of the chemistry developed previously during said heating step.

Claim 29

A method of making a silicon nitride comprising body useful as a starting material in the hot pressing of objects, comprising the steps of: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent, and a glass forming agent, said oxynitride and glass forming agents being present in said mixture in an amount to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 , oxynitride crystallites encapsulated by 0.2-1% silicate by weight, with up to 0.5% by weight free silicon and unreacted agents; and (b) heating the compact in a nitriding atmosphere, without the use of pressure normally associated with hot pressing, to produce said converted compact consisting of Si 3 N 4 , at least one dispersed silicon oxynitride crystallite phase encapsulated by 0.2-1% by weight of the silicate, and up to 0.5% by weight free silicon and unreacted agents.

Claim 30

A method of making a silicon nitride comprising body useful as a starting material in the hot pressing of objects, comprising the steps of: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent, and a glass forming agent, said oxynitride and glass forming agents being present in said mixture in an amount to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 , oxynitride crystallites encapsulated by 0.2-1% silicate by weight, with up to 0.5% by weight free silicon and unreacted agents; and (b) heating the compact in a nitriding atmosphere, without the use of pressure normally associated with hot pressing, to produce said converted compact consisting of Si 3 N 4 , at least one dispersed silicon oxynitride crystallite phase encapsulated by 0.2-1% by weight of the silicate, and up to 0.5% by weight free silicon and unreacted agents.

Claim 37

A method of making a reaction bonded, hot pressed silicon nitride comprising object having resistance to oxidation at high temperatures, comprising: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent, present in an amount to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 and oxynitride crystallites, and a glass forming agent selected from the group consisting of MgO, Fe 2 O 3 , CaO and Cr 2 O 3 in an amount from 0.4-1.0% sufficient to encapsulate said oxynitride crystallites by a glass film; (b) heating said compact in a nitriding atmosphere to produce said converted compact, said converted compact having a size greater than and a density less than the final object to be formed; and (c) hot pressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising object of required dimension and a density useful for a cutting tool and consisting essentially of the chemistry in said converted compact.

Claim 38

A method of making a reaction bonded, hot pressed silicon nitride comprising object having resistance to oxidation at high temperatures, comprising: (a) forming a compact from a mixture of silicon with from 1 to 3% SiO 2 associated therewith, an oxynitride forming agent, present in an amount to substantially fully react said silicon upon heating in nitrogen to convert the compact to essentially Si 3 N 4 and oxynitride crystallites, and a glass forming agent selected from the group consisting of MgO, Fe 2 O 3 , CaO and Cr 2 O 3 in an amount from 0.4-1.0% sufficient to encapsulate said oxynitride crystallites by a glass film; (b) heating said compact in a nitriding atmosphere to produce said converted compact, said converted compact having a size greater than and a density less than the final object to be formed; and (c) hot pressing said body at a temperature equal to or below 1670° C. to produce a silicon nitride comprising object of required dimension and a density useful for a cutting tool and consisting essentially of the chemistry in said converted compact.

Claim 39

A method of making a reaction bonded, hot pressed silicon nitride comprising cutting tool which has increased oxidation resistance at 1000° C., comprising the steps of: (a) forming a compact from a mixture of silicon, SiO 2 , Y 2 O 3 and Al 2 O 3 reactive with SiO 2 and Y 2 O 3 to form upon heating a controlled amount of a protective amorphous silicate glass, said Y 2 O 3 being present in said mixture in an amount of 3-19% by weight of said silicon, said Al 2 O 3 being present in an amount of at least 0.4 and up to 5% by weight of said silicon, said SiO 2 being present in an amount of 1-3% by weight of said silicon, and said mixture having a Y 2 O 3 /SiO 2 ratio of 1:1-6:4; (b) heating said compact in a nitriding atmosphere to produce a silicon nitride comprising body consisting of Si 3 N 4 , at least one yttrium silicon oxynitride present in an amount of 3-15% by weight of said body and dispersed throughout, up to 0.5% free silicon and residual Y 2 O 3 , 1% or less silicate glass encapsulating said yttrium silicon oxynitride, at lease 60% of said Si 3 N 4 being in the alpha form, said body having a size greater than and a density less than said tool; (c) hot pressing said body at an ultimate temperature of 1200°-1650° C. in an environment uncontrolled as to inertness to produce a silicon nitride comprising cutting tool of required dimension and density consisting essentially of the chemistry developed previously during said heating step.

Claim 40

A method of making a reaction bonded, hot pressed silicon nitride comprising cutting tool which has increased oxidation resistance at 1000° C., comprising the steps of: (a) forming a compact from a mixture of silicon, SiO 2 , Y 2 O 3 and Al 2 O 3 reactive with SiO 2 and Y 2 O 3 to form upon heating a controlled amount of a protective amorphous silicate glass, said Y 2 O 3 being present in said mixture in an amount of 3-19% by weight of said silicon, said Al 2 O 3 being present in an amount of at least 0.4 and up to 5% by weight of said silicon, said SiO 2 being present in an amount of 1-3% by weight of said silicon, and said mixture having a Y 2 O 3 /SiO 2 ratio of 1:1-6:4; (b) heating said compact in a nitriding atmosphere to produce a silicon nitride comprising body consisting of Si 3 N 4 , at least one yttrium silicon oxynitride present in an amount of 3-15% by weight of said body and dispersed throughout, up to 0.5% free silicon and residual Y 2 O 3 , 1% or less silicate glass encapsulating said yttrium silicon oxynitride, at lease 60% of said Si 3 N 4 being in the alpha form, said body having a size greater than and a density less than said tool; (c) hot pressing said body at an ultimate temperature of 1200°-1650° C. in an environment uncontrolled as to inertness to produce a silicon nitride comprising cutting tool of required dimension and density consisting essentially of the chemistry developed previously during said heating step.