Revisiting 1 GPa alumina ceramics

Sintering is the proof test of ceramic processing. So is flaw-sensitive flexural strength. Calibration and optimization of the processing are critical to the further development of ceramic science and technology. Chasing ultra-strength in brittle ceramics such as alumina is thus significant in the sense that it best illustrates how one can eliminate flaws via powders, forming, and sintering. Previous reports in high-strength alumina with three-point-bending strength above 1 GPa are rare, while some cause confusion and suspicion. Here we revisited the processing of 1 GPa alumina ceramics by centrifugal casting and pressureless two-step sintering. We demonstrated high green body density of 63%, low pressureless sintering temperature of 1175^oC, high sintered density of 99.2%, fine grain size of 0.52 μm, and high flexural strength of 1036±32 MPa (three point bending over 20 mm span length). We hope our study could set down the questioning on 1 GPa alumina: It is doable and can be done better.