Fabrication of Functionally Graded ZTA Ceramics Using a Novel Combination of Freeze Casting and Electrophoretic Deposition
Functionally graded zirconia toughened alumina (ZTA) ceramics have been fabricated from aqueous suspension with an open porous and aligned lamellae structure on one side and a dense layer on the other side. A novel combination of two processes has been merged to achieve such graded structures, i.e. unidirectional freeze casting and electrophoretic deposition (EPD). A custom-designed apparatus has been built in which a controlled double side cooling has been realized in conjunction with the possibility to introduce an electric field over the ceramic slurry prior to the freezing process. A square wave pulsed DC voltage has been used in the EPD process in order to avoid electrolysis of water. Suitable duty cycle of applied pulse voltage could gain bubble-free deposition. The thickness of the dense layer is controlled by tuning voltage, duty of cycle, pulse width and deposition time. It was shown that thicknesses up to 500μm could be achieved. The microstructure of the porous part is controlled by adjusting the temperature during the freezing process. Using temperatures between -1 and -25°C the channel width changed from 220 to 40μm, respectively.
Pietro VINCENZINI, Ralf RIEDEL, Alexander G. MERZHANOV and Chang-Chun GE
A. Preiss et al., "Fabrication of Functionally Graded ZTA Ceramics Using a Novel Combination of Freeze Casting and Electrophoretic Deposition", Advances in Science and Technology, Vol. 63, pp. 340-347, 2010