Spark plasma sintering of translucent polycrystalline α/β-silicon nitride ceramics with Y2O3 additive

Translucent polycrystalline alpha/beta-silicon nitride ceramics had been fabricated for the first time by spark plasma sintering from alpha-Si3N4 starting powder with 2 wt% Y2O3. It aimed to investigate the influence of process pa-rameters on the phase evolution, microstructural development, and mechanical properties of sintered ceramics. The increase in sintering temperature from 1750 degrees C to 1800 degrees C under 25 MPa considerably raised relative density, promoted alpha-beta phase transformation, increased hardness and fracture toughness values, and exhibited translucency in the visible region. Furthermore, the highest relative density (98%), hardness (-HV: 14.9 GPa), fracture toughness (-9.8 MPa m1/2) values, and a higher degree of translucency were achieved with the increment of uniaxial pressure from 25 to 50 MPa at 1750 degrees C. These results indicated that translucent poly-crystalline alpha/beta-silicon nitride ceramics, produced by liquid phase assisted spark plasma sintering at 1750 degrees C under 50 MPa, can be used as transparent armors and visible windows under harsh conditions.