From defect control to mechanical enhancement: A pathway via X-ray computed tomography for vat photopolymerization additive manufactured Al₂O₃ ceramics

The printing process is the most critical step in the vat photopolymerization (VPP) additive manufacturing of ceramics, as the formation of internal defects can significantly compromise the mechanical properties and structural integrity. However, conventional research methodologies are insufficient for the quantitative characterization of defects and are even inadequate for the effective control of defect formation. This study systematically investigates the printing process for fabricating high-performance Al₂O₃ ceramics, with a focus on understanding and controlling defects. An orthogonal experiment was designed to investigate the effects of three critical factors on the mechanical properties and relative density of the Al₂O₃ ceramic sintered body. The results showed that slicing thickness exerted the most significant influence on flexural strength, followed by irradiance, while exposure time had the least impact. The optimal parameter combination was identified as 12000 µW/cm², 4 s, 100 µm, respectively. Internal defects in both green and sintered body and their formation mechanisms were 3D quantitatively characterized using X-ray computed tomography (X-CT). X-CT analysis revealed the presence of pore defects in the green body, while both pore and delamination defects were identified in the sintered body. Appropriate slicing thickness enhances interlayer bonding by facilitating adequate secondary photopolymerization, which significantly reduces delamination defects and controls their formation. This work establishes X-CT as a powerful tool for non-destructive analysis in additive manufactured ceramic.