Microstructure evolution and toughening mechanism of Al2O3/YSZ directionally solidified eutectic ceramic

Abstract

Al2O3/YSZ directionally solidified eutectic ceramics (DSECs) with a diameter of 10 mm were prepared via the induction heating zone melting (IHZM), and effects of the pulling rate of the crucible on the microstructure and mechanical properties were investigated. The eutectic components included α-Al2O3, t-ZrO2 and m-ZrO2 phases. The DSECs’ microstructure evolved from a mixture of discontinuous lamellar and round colony structure to the round colony structure, then to the faceted colony structure, and finally to a cell structure with increasing the pulling rate. The formation kinetics and growth process of the round colony structure were described and discussed in detail. The reason that the faceted colony structure formed could attributed to the large increase of solid-liquid interface curvature. When the pulling rate was 300 mm/h, the actual growth rate vg = 81.9 ± 17.5 mm/h was calculated from λ2v=37.7 corresponding to the intracolony; or vg = 99.5 ± 58 mm/h was calculated from with λ2v=631 corresponding to the intercolony. The DSECs’ hardness and fracture toughness increased with the pulling rate, and got the maximum values of 18.6 GPa and 9.39 MPa m1/2 at 300 mm/h, respectively, which could be attributed to the refinement of phases and the decrease of m-ZrO2 phase fraction.