Directed laser deposition of Al2O3–ZrO2 melt-grown composite ceramics with multiple composition ratios

Abstract

Melt-grown Al2O3–ZrO2 hypoeutectic, eutectic and hypereutectic ceramics were fabricated using directed laser deposition (DLD) technology. Flexural strength of DLD-fabricated Al2O3–ZrO2 composites was obtained for the first time. Toughening mechanisms of ZrO2 in different composition ratios were revealed. The results show that hypoeutectic ceramics form composite microstructure with α-Al2O3 primary dendrites discretely distributing in eutectic continuous matrix, while the discrete phase becomes t-ZrO2 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 m1/2 under hypereutectic composition, which is 16.8% higher than that of eutectic ratio. Primary t-ZrO2 dendrites in hypereutectic ceramics have phase transformation toughening effect. However, as a eutectic structure phase, t-ZrO2 in hypoeutectic and eutectic ceramics has no phase transformation toughening effect because its size is smaller than the critical size of phase transformation.