| 摘要 |
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 0.50-2.5 Al2O3 is prepared. The mixture is hot pressed at a temperature of 1,680 DEG -1,750 DEG 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 DEG -1,400 DEG 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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