Mechanical properties of melt-grown Al2O3–ZrO2(Y2O3) eutectics with different microstructure

The effect of the microstructure on the mechanical properties of Al2O3–ZrO2(Y2O3) eutectic ceramic oxides was studied. Rods processed by the laser-heated floating zone method with three different microstructures were obtained as the growth rate increased: a homogeneous dispersion of irregular ZrO2 lamellae within the Al2O3 matrix, colonies with a core containing a dispersion of submicron ZrO2 lamellae or rods surrounded by a thick intercolony region, and elongated cells formed by a dispersion of very fine ZrO2 lamellae and separated by thin intercellular boundaries. The average flexure strength (close to 1.6 GPa) of the eutectics made up of a homogeneous dispersion of ZrO2 lamellae was outstanding, and they also presented an excellent Weibull modulus (12.9) when the microstructure was homogeneous throughout the sample. Banding did not affect the average strength but degraded the Weibull modulus. In general, the flexure strength decreased as the size of the main morphological features of the microstructure (colony or cell diameter) increased. The thickness of the intercellular boundaries increased with the Y2O3 content and, above a critical value, reduced dramatically the strength by activating a new failure mechanism based on the coalescence of the pores and shrinkage cavities concentrated at the intercellular boundaries.