Tailored graded pore structure in zirconia toughened alumina ceramics using double-side cooling freeze casting

Ceramics with graded and continuously aligned open pores were investigated using a double-side cooling freeze casting setup. The ceramic preforms with tailored lamellae spacing (wavelength), wall thickness and graded pore structure were used to infiltrate with a second phase for the fabrication of graded interpenetrating phase composites. The effects of solid content, temperature setting and gradient, cooling rate and the introduction of electrophoretic deposition (EPD) on the freezing velocity of the ceramic suspension were analysed. On the bottom of the ceramic specimen, a dense layer was formed and tailored with the use of EPD. The ceramic was characterised by a graded open pore structure with wavelengths up to 115 μm and interconnected microstructure. The effect of solid content on the degree of supercooling and the effect of temperature gradient on the average freezing velocity were investigated. The addition of EPD before freeze casting affected significantly the microstructure, the wavelength decreased and the wavelength gradient became smaller compared to simple freeze casting.