Functionally graded ceramic and ceramic  /metal composites shaped by electrophoretic deposition S. Put, J. Vleugels, G. Anne ´, O. Van der Biest * Department of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 44, B-3001 Leuven, Belgium Abstract 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. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Electrophoretic deposition (EPD); Functionally graded materials (FGM); Ceramic composites; Hardmetals 1. Introduction At present, there is a tremendous industrial need for materials with major tribological engineering applications. In the processing of monolithic components, the main challenge is to combine irreconcilable properties in the same component, such as high hardness at high temperatures and structural toughness at low temperatures. A pos- sible concept to meet this demand is that of functionally graded materials (FGM). FGMs offer a solution by developing, for example, a graded material with a tough core and a hard surface. A wide variety of available processes have been reported for FGM production, such as plasma spraying, centrifugal casting, common powder metallurgy, PVD, CVD, and colloidal processing [1]. Amongst these processes, electrophoretic de- position (EPD) is a fairly rapid low cost process, capable of producing continuously graded materi- * Corresponding author. Tel.:  /32-1632-1264; fax:  /32- 1632-1992. E-mail address: omer.vanderbiest@mtm.kuleuven.ac.be (O. Van der Biest). Colloids and Surfaces A: Physicochem. Eng. Aspects 222 (2003) 223  /232 www.elsevier.com/locate/colsurfa 0927-7757/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0927-7757(03)00227-9