Process for producing Si3 N4 base articles by the cold press sinter method

Claim 1

A method of making Si 3 N 4 based cutting tools, comprising: (a) pressing a uniform mixture of three powders at ambient conditions to a density substantially less than full density, the base powder constituting at least 75% by weight of said mixture and consisting of crystalline Si 3 N 4 , the second powder being selected from the group consisting of Y 2 O 3 , MgO, CeO 2 , ZrO 2 and mixtures thereof, the third powder being selected from the group consisting of Al 2 O 3 , WC, WSi 2 , W, TiC and mixtures thereof, said Al 2 O 3 , when selected, being limited to no more than 4%, said powders being regulated in particle size to one micron or less; (b) in the absence of substantial mechanical pressure, sintering said pressed mixture equal to or greater than 99% theoretical density under an inert atmosphere.

Claim 2

A method of making Si 3 N 4 based cutting tools, comprising: (a) pressing a uniform mixture of three powders at ambient conditions to a density substantially less than full density, the base powder constituting at least 75% by weight of said mixture and consisting of crystalline Si 3 N 4 , the second powder being selected from the group consisting of Y 2 O 3 , MgO, CeO 2 , ZrO 2 and mixtures thereof, the third powder being selected from the group consisting of Al 2 O 3 , WC, WSi 2 , W, TiC and mixtures thereof, said Al 2 O 3 , when selected, being limited to no more than 4%, said powders being regulated in particle size to one micron or less; (b) in the absence of substantial mechanical pressure, sintering said pressed mixture equal to or greater than 99% theoretical density under an inert atmosphere.

Claim 4

A method of making Si 3 N 4 based cutting tools, comprising: (a) cold pressing a uniform mixture of three powders, each powder having a particle size of less than one micron to form a compact having a desired cutting tool configuration with a cold compacted density of 50-70%, one of said powders being constituted of crystalline silicon nitride and constituting at least 75% by weight of said mixture, a second of said powders constituting 2-10% by weight of said mixture and having its ingredients selected from the group consisting of Y 2 O 3 , NgO, CeO 2 and ZrO 2 , the third of said powders constituting 2-23% of said mixture by weight and having its ingredients selected from the group consisting of Al 2 O 3 , WC, WSi 2 , W and TiC, said Al 2 O 3 being limited to 4.5% when selected; (b) sintering said cold pressed material at a temperature of 1650°-1750° C. for at least 15 minutes and under the protection of an inert atmosphere at a pressure of one atmosphere or more.

Claim 5

A method of making Si 3 N 4 based cutting tools, comprising: (a) cold pressing a uniform mixture of three powders, each powder having a particle size of less than one micron to form a compact having a desired cutting tool configuration with a cold compacted density of 50-70%, one of said powders being constituted of crystalline silicon nitride and constituting at least 75% by weight of said mixture, a second of said powders constituting 2-10% by weight of said mixture and having its ingredients selected from the group consisting of Y 2 O 3 , NgO, CeO 2 and ZrO 2 , the third of said powders constituting 2-23% of said mixture by weight and having its ingredients selected from the group consisting of Al 2 O 3 , WC, WSi 2 , W and TiC, said Al 2 O 3 being limited to 4.5% when selected; (b) sintering said cold pressed material at a temperature of 1650°-1750° C. for at least 15 minutes and under the protection of an inert atmosphere at a pressure of one atmosphere or more.