Defect evolution in vat photopolymerization additive manufactured Al₂O₃ ceramics during sintering: Correlation with microstructure and mechanical properties

Defects formed during vat photopolymerization (VPP) of ceramics degrade their mechanical properties. The sintering process can introduce, amplify, or transform defects that originate from slurry preparation, stereolithography, and debinding processes. However, the change of these defects and their effect on mechanical properties remains unclear. This study systematically investigates the role of sintering temperature and holding time on the microstructure and mechanical properties of VPP prepared Al₂O₃ ceramic. Using three-dimensional X-ray computed tomography (X-CT), the changes, formation mechanisms, morphology, and quantity of internal defects (pores and delamination) are quantitatively characterized. The results demonstrate that sintering temperature is the predominant factor influencing densification and flexural strength due to its effect on the defects. The transformation behavior of delamination defects was revealed. The total defect rate significantly decreased from 1.10% to 0.23%, primarily through the shrinkage, separation, and disappearance of delamination defects, while pores gradually reduced or were even eliminated. This work establishes that optimizing the sintering profile is a crucial strategy for defect control, resulting in a ≈100% enhancement in flexural strength. This advancement enables the full potential of VPP prepared Al₂O₃ ceramics to be realized for structural applications.