| 摘要 |
<p>A method for the manufacture of a tool and a unit object based on silicon nitride is described. A uniform powder mixture of Si3N4 containing SiO2 as an oxide coating, 4 - 12% by weight of Y2O3 and 0.50-2.5 of Al2O3 is prepared. The mixture is hot pressed at a temperature of 1680-1750 degree C under pressure for a period of time sufficient to produce at least 99.0% (and preferably at least 99.5%) of the full theoretical density of the mixture in order to obtain a pressed object. Heat and pressure are removed and the object is cooled. The object is treated by heating it and maintaining it at a temperature in the range 1000-1400 degree C without mechanical pressure for at least 5 minutes but for sufficient time for a nucleation reaction to take place in secondary phases formed as a result of the hot pressing. The heat treatment can also be applied as an interruption in the cooling cycle or as a subsequent reheating cycle after cooling to ambient temperature.</p> |
