Microstructure and Mechanical Properties of Hot‐Pressed α‐Al ₂ O ₃ ‐Seeded γ‐Alumina Ceramics

High‐quality alumina ceramics were fabricated by a hot pressing with MgO and SiO ₂ as additives using α‐Al ₂ O ₃ ‐seeded nanocrystalline γ‐Al ₂ O ₃ powders as the raw material. Densification behavior, microstructure evolution, and mechanical properties of alumina were investigated from 1250°C to 1450°C. The seeded γ‐Al ₂ O ₃ sintered to 98% relative density at 1300°C. Obvious grain growth was observed at 1400°C and plate‐like grains formed at 1450°C. For the 1350°C hot‐pressed alumina ceramics, the grain boundary regions were generally clean. Spinel and mullite formed in the triple‐grain junction regions. The bending strength and fracture toughness were 565 MPa and 4.5 MPa·m ^1/2 , respectively. For the 1300°C sintered alumina ceramics, the corresponding values were 492 MPa and 4.9 MPa·m ^1/2 .