Directed laser deposition of Al 2 O 3 –ZrO 2 melt-grown composite ceramics with multiple composition ratios

Melt-grown Al 2 O 3 –ZrO 2 hypoeutectic, eutectic and hypereutectic ceramics were fabricated using directed laser deposition (DLD) technology. Flexural strength of DLD-fabricated Al 2 O 3 –ZrO 2 composites was obtained for the first time. Toughening mechanisms of ZrO 2 in different composition ratios were revealed. The results show that hypoeutectic ceramics form composite microstructure with α-Al 2 O 3 primary dendrites discretely distributing in eutectic continuous matrix, while the discrete phase becomes t-ZrO 2 in hypereutectic ceramics. Eutectic ceramic has lamellar fine eutectic colony structure. Hypoeutectic ceramics show the best hardness, while eutectic ceramics have the highest flexural strength of 237 MPa. Fracture toughness reaches the maximum of 5.91 MPa m 1/2 under hypereutectic composition, which is 16.8% higher than that of eutectic ratio. Primary t-ZrO 2 dendrites in hypereutectic ceramics have phase transformation toughening effect. However, as a eutectic structure phase, t-ZrO 2 in hypoeutectic and eutectic ceramics has no phase transformation toughening effect because its size is smaller than the critical size of phase transformation.