Effect of sintering additives on the nitridation behavior of reaction-bonded silicon nitride

The microstructures and nitridation behavior of reaction-bonded silicon nitride (RBSN) bodies, containing two types of sintering additives (6 wt.% Y2O3–2 wt.% Al2O3 (6Y2A) and 6 wt.% Y2O3–2 wt.% MgO (6Y2M)), were investigated. In using the 6Y2A sintering additive, the silicon compacts were nitrided from the surface to the interior region while in the 6Y2M system, the nitridation occurred from the interior to the exterior region of the compact. The relative density and percent of nitridation of the RBSN body using 6Y2A sintering additive showed lower values than those using 6Y2M sintering additive, but the phase ratio of β/(α + β) showed a higher value in the RBSN body using the 6Y2A sintering additive. All of the Si3N4 grain boundaries and triple junctions were covered with amorphous phase independent of the sintering additives.