Transparent polycrystalline alumina obtained by SPS: Single and double doping effect

Commercial nanocrystalline alpha alumina powders were used for fabrication of dense and transparent alumina by spark plasma sintering (SPS). High purity dopants such as MgO, Y₂O₃, TiO₂ and CaO with 150 ppm amount were added to alumina and powder mixtures were densified by SPS between 1175 and 1300^°C using 80 MPa pressure for 5 to 20 min durations. The influences of MgO, Y₂O₃, TiO₂ and CaO single and double doping on density, hardness, fracture toughness and microstructures of alumina samples are investigated. The highest hardness value was measured as 24.2 GPa in the sample doped with 150 ppm MgO and 150 ppm CaO sintered at 1175^°C under 80 MPa pressure for 20 min. The fracture toughness values were ranged between 3.3 and 4.9 MPa.m^1/2. Alumina ceramic with 150 ppm MgO which was spark plasma sintered at 1175 ^°C for 20 min showed the highest Real Inline Transmittance (RIT) value as 55.5%.