Sintering and Properties of Si3N4 with and Without Additives by HIP (Hot Isostatic Pressing) Treatment

摘要

Hot Isostatic Pressing (HIP) of Si3N4 powders with and without additives was performed using a glass container, and various kinds of pressureless-sintered Si3N4 were HIP'ed without a container. The effects of HIP treatment on density, microstructure, flexural strength, microhardness, and fracture toughness on Si3N4 ceramics were studied. Using a glass container it was difficult to reach theoretical density. The microhardness of HIP'ed Si3N4 without additives was low, and the fracture toughness of HIP'ed Si3N4 with and without additives was 22 to 25 W/m-K, and it decreased with increasing the amount of additives. The density and flexural strength, and hardness of pressureless-sintered Si3N4 which contained Al2O and Y2O3 as oxide additives were remarkably improved by HIP treatment using nitrogen as a pressure transmitting gas. It is very important to select the sintering conditions for fabricating the presintered body of Si3N4 in order to improve the mechanical properties of Si3N4 by HIP treatment.