Functionally graded ceramic and ceramic–metal composites shaped by electrophoretic deposition

Because of the increasing interest in colloidal processing methods for shaping advanced technical ceramics and hardmetals, the potential of electrophoretic deposition as a shaping process is investigated. The mechanisms of deposition, which have been proposed in literature, and the relation between the evolution of the current, yield and the electric field strength are evaluated. Special attention is given to the electrophoretic characteristics of the constituent powders, such as the point of zero charge, the natural pH, the electrophoretic mobility, the effective particle charge and the resistance of the suspension. The investigated materials comprise alumina, zirconia and their composites as well as various formulations of hardmetals. The fabrication of homogeneous as well as continuously graded plate-shaped components is highlighted. The main feature of a functionally graded material (FGM) is the position-dependant composition and related mechanical properties. Moreover, a mathematical model of the EPD process for FGMs is presented that allows to predict the composition and slope of the gradient in the sintered material from the starting composition of the suspensions, the EPD process parameters and the powder specific EPD characteristics. The correlation between the experimental results and the predicted gradient profile is excellent.