Method of making silicon nitride based cutting tools - i

Details Method of making silicon nitride based cutting tools - i Method of making silicon nitride based cutting tools - i

C - Chemistry, Metallurgy

04

B

25/133, 25/140

C04B 35/58 (2006.01) C04B 35/593 (2006.01)

Patent

CA 1142334

-10- Abstract of the Disclosure A method of making a unitary silicon nitride comprising object and tool is disclosed. A uniform powder mixture of Si3N4 containing SiO2 as an oxide coating, 4-12% by weight Y2O3, and .50-2.5 Al2O3 is prepared. The mixture is hot pressed at a temperature of 1,680-1,750°C under a pressure and for a period of time sufficient to produce at least 99.0% (preferably at least 99.5%) of full theoretical density in the mixture to form a pressed object. The heating and pressure is then relieved and the object cooled. The object is heat treated by holding at a temperature in the range of 1,000-1,400°C without mechanical pressure for at least 5 minutes but for a time sufficient to provide a nucleating reaction in secondary phases formed as a result of hot pressing. The heat treatment can take place either as an interruption of the cooling cycle or as a subsequent reheat cycle after cooling to room temperature.

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