Alumina (Al2O3) is a structural ceramic that has exceptional mechanical strength, superior chemical inertness and biocompatibility, making it an appealing candidate for various engineering and medical applications. Despite these advantages, the inherent brittleness hinders its wide applications. The lack of dislocations and the restricted dislocation mobility arising from the strong covalent bonds and ionic character in the crystal structure makes it fracture catastrophically at room temperature before plastic deformation can occur.

 

In this thesis, various strategies ranging from the sintering processes to post-processing thermomechanical treatment have been utilized to investigate the toughening mechanisms in Al2O3. Field-assisted sintering methods were employed to consolidate high quality Al2O3 effectively. During flash sintering, abundant defects including dislocations, stacking faults, and twins are introduced as plasticity carriers within the nonequilibrium sintering process, thereby enhancing the plastic deformability of Al2O3. In comparison, spark plasma sintering enables the formation of ultrafine grains at reduced temperatures and short sintering times, promoting grain boundary sliding at elevated temperatures and contributing to overall plastic deformability under stress. Building on the known behavior of ceramics that deform at elevated temperatures, preloading experiments were designed to artificially pump defects into the ceramics during high-temperature deformation, which subsequently enhances room temperature deformability. Finally, zirconia (ZrO2), known for its tetragonal to monoclinic transformation, has been integrated into the Al2O3 matrix to increase the plasticity by obstructing the crack propagation. Through meticulous microstructure tuning and defect engineering, along with in-situ SEM micropillar compression testing and detailed microstructure analysis using transmission electron microscopy, this thesis elucidates the toughening mechanisms of Al2O3, reveals various methods to improve ceramic deformability and reflects the potentials to create ductile ceramics for broad future applications.