Bending strength of density‐controlled alumina fabricated by direct ink writing

Abstract In this study, density‐controlled (DC) alumina components with tailored density gradients were fabricated via direct ink writing (DIW) using bimodal powder mixtures composed of fine and coarse alumina powders. The slurry compositions were systematically adjusted to achieve target density distributions, and the resulting print quality and mechanical performance—particularly bending strength—were thoroughly evaluated. Distortion at the interfaces between regions of different densities was observed, primarily due to slurry inflow into gaps between previously deposited filaments and the substrate. DC alumina specimens with a significant internal density contrast exhibited edge‐initiated interfacial cracking, attributed to tensile stresses induced by differential shrinkage. The magnitude of these internal stresses exceeded the calculated material strength by a factor of 1.89, leading to failure. Finite element analysis was employed to investigate the stress distribution and to assess the impact of shrinkage mismatch on structural integrity. Notably, certain density configurations yielded higher bending strength than their uniformly dense counterparts, while others showed comparable performance. These results demonstrate both the potential of controlling internal density to tailor mechanical properties and the key challenges associated with multimaterial DIW of ceramics, particularly in managing interfacial stress concentrations and shrinkage‐induced defects.