Microstructure and mechanical properties of ZrO2 fiber toughened Al2O3/ZrO2(Y2O3) solidified ceramics prepared with high frequency induction zone melting

ZrO2 fiber toughened and non-fiber toughened Al2O3/ZrO2(Y2O3) directionally solidified eutectic ceramics (DSECs) were prepared via high frequency induction zone melting method, and the effects of both the fibers and the growth rate on the microstructure and mechanical properties were investigated. The results showed that both the fiber toughened and the non-fiber toughened DSECs were composed of α-Al2O3, c-ZrO2 and m-ZrO2, and their microstructures were all typical colony structure. The phase spacing in intracolony (λ) for these two kinds of DSECs gradually decreased with the increase of growth rate (ν), they satisfied λ = 10.31ν−1/2 and λ = 13.65 v−1/2, respectively. And the minimum values of λ were 2.33 ± 0.25 µm and 2.99 ± 0.17 µm, respectively, i.e., that is ZrO2 fiber decreased the phase spacing in intracolony about 22%. The fracture toughness for these two DSECs increased continuously with the growth rate, reached the maximum values of 5.72 ± 0.20 MPa m1/2 and 3.95 ± 0.23 MPa m1/2 at 30 mm/h, respectively, i.e., the former was about 1.45 times of the latter. At the same growth rate, the fracture toughness of ZrO2 fiber toughened DSEC were obviously higher than those of DSEC without fiber. When they encounter fibers with high elastic modulus during their propagation, the cracks will undergo deflection, bifurcation, or bridging, and the fibers will undergo debonding and pulling-out under the external stress, both of which consume a large amount of crack propagation energy and achieve toughening effect.