Effect and mechanism of ZrO 2 doping on the cracking behavior of melt‐grown Al 2 O 3 ceramics prepared by directed laser deposition

Directed laser deposition (DLD) is a new method for rapidly preparing melt‐grown ceramics, but cracking problem greatly limited its application. In this study, cracking behavior of Al 2 O 3 ceramics was suppressed by doping ZrO 2 . Crack suppression mechanism of ZrO 2 doping in melt‐grown ceramics was also analyzed. Process parameters which are prone to generating cracks were adopted in the experiments, and they contribute to showing the crack clearly. Results show that ZrO 2 doping has remarkable crack suppression effects. It is most obvious when ZrO 2 content is 37 mol%. Compared with those of pure Al 2 O 3 ceramics, crack density reduces by 43.2%, and the number of longitudinal main cracks reduces by 63.2%. Doping of ZrO 2 forms dense composite microstructure with primary α‐Al 2 O 3 grains discretely distributing in eutectic continuous matrix. Therefore, initial crack sources are effectively reduced. Morphology of primary Al 2 O 3 grains transforms from cellular to dendritic, which changes crack propagation mode from inter‐granular to trans‐granular. Mismatch of thermo‐physical properties of different phase promotes the arrest, deflection, and bridging phenomena in crack propagation, contributing to crack suppression. On the basis of ZrO 2 doping, we have realized the preparation of crack‐free eutectic ceramic (37 mol%ZrO 2 ) samples through further process optimization. The maximum size of the sample reaches 230 mm.