"Plasticity Enhancement and Sintering Mechanisms of Alumina-based Binary Phase Ceramics Processed by Field-assisted Sintering" 

Shiyu Zhou, MSE PhD Candidate 

Advisor: Professor Haiyan Wang

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This dissertation investigates plasticity enhancement and sintering mechanisms of alumina-based binary phase ceramics processed by field-assisted sintering. To address the intrinsically high sintering temperature, limited plastic deformability, and brittle fracture behavior of Al2O3-based ceramics, this work develops secondary-phase, phase-boundary, current-pathway, and multilayer architecture strategies using flash sintering and spark plasma sintering. First, phase-boundary assisted flash sintering is demonstrated in Al2O3 -TiO2 nanocomposites. A temperature-field-composition processing map shows that TiO2 addition and higher applied electric fields significantly reduce the flash sintering temperature of Al2O3, while simulations reveal that localized Joule heating, electric-field concentration, and stress accumulation at Al2O3-TiO2 interfaces promote densification. Second, the heating-rate effect in SPS-processed Al2O3-TiO2 nanocomposites is clarified, showing that optimized heating rate improves hardness and fracture toughness through refined grains, preferred texture, and stress-responsive defect evolution. Third, trilayer-assisted flash sintering is developed for 50ZTA and AT50 ceramics, revealing a current-density-governed transition from phase-selective sintering to effective co-sintering and substantially improved mechanical properties. In situ micropillar compression further demonstrates enhanced high-temperature deformability in trilayer 50ZTA, enabled by phase transformation, stacking fault formation, crack deflection, and interfacial strain accommodation. Finally, a field-multiplied 3YSZ-Al2O3-3YSZ architecture enables pure Al2O3 to flash sinter at reduced apparent fields and temperatures by concentrating voltage across the Al2O3 layer. Overall, this dissertation establishes field, current, phase boundaries, and architecture as active tools for designing damage-tolerant oxide ceramics