Properties and microstructure of hot isostatically pressed Si 3N 4

Abstract

The hot isostatic pressing (HIP) of Si 3N 4 was performed in the temperature range 1500–1800°C and within the pressure range 90–172 MPa. Both additive-free Si 3N 4 and Si 3N 4 with Y 2O 3 additions were studied. During the HIP process the transformation of α- Si 3 N 4 to β- Si 3 N 4 occurs and the amount of α→ β transformation increases as the HIP temperature and HIP pressure increase. The α→ β transition also depends on the Y 2O 3 content. The density of the Si 3N 4 consolidated by HIP increases as the HIP pressure, HIP temperature and Y 2O 3 content increase. The hardness and Young's modulus of the product increase gradually with increasing Y 2O 3. The effect of outgassing the starting material prior to HIP on the properties of the final product is discussed.