Effects of Growth Rate on Microstructure and Properties of Directionally Solidified Eutectic Ceramic Al2O3/MgAl2O4/ZrO2

Directionally solidified Al2O3/MgAl2O4/ZrO2 ternary eutectic ceramic was prepared by means of induction heating zone melting (IHZM), and the effects of the growth rate on the microstructure and properties of the solidified ceramic were investigated. X-ray diffraction (XRD) patterns showed that the eutectic rod contained Al2O3, MgAl2O4 and ZrO2 phases. The results of scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) demonstrated that Al2O3/MgAl2O4 constituted the matrix of the eutectic ceramic while rod-like ZrO2 was uniformly embedded in the matrix. The specimen morphology is transformed from an irregular pattern to a regular bar-shaped pattern with the increase in the growth rate. The measured and calculated value of lambda(2)nu (lambda, the phase spacing; nu, the solidification rate) was approximately equal to 2.98, which fitted well with the formula: lambda(2)nu = constant. With the increase in the growth rate, the hardness of the material decreases, the fracture toughness first increases and then decreases. The maximum hardness of the solidified eutectic ceramic rate reached 11.68 GPa when the solidification rate was 1 mm/h, this hardness was about 1.6 times that of the pre-sintered sample. Its maximum fracture toughness at room temperature was 7.21 MPa.m(1/2) when the rate was 3 mm/h, which was about two times that of the pre-sintered sample.