Laminated and functionally graded ceramics by electrophoretic deposition. O. Van der Biest 1, a , L. Vandeperre b , S. Put c , G. Anné d , J. Vleugels e 1 Department of Metallurgy and Materials Engineering, K.U. Leuven, Kasteelpark Arenberg, 44, 3001, Heverlee, Belgium a omer.vanderbiest@mtm.kuleuven.be, b ljmv2@cam.ac.ukl, c stijn.put@umicore.com, d guy.anne@bekaert.com, e jozef.vleugels@mtm.kuleuven.be Keywords: Electrophoretic deposition, EPD, functionally graded materials, FGM Abstract. Electrophoresis is the effect that when an electric field is applied to a suspension of a powder in a liquid, the powder particles move under influence of this field. Frequently the powder particles also deposit at one of the electrodes. The form of the electrode determines the form of the deposit, hence shaping is possible. The current insights into the science and technology of electrophoretic deposition (EPD) will be summarized. EPD is well suited for shaping layered microstructures (laminates), by simply changing repeatedly between two or more suspensions during deposition. Tubular laminates consisting of silicon carbide layers and crack deflecting graphite interlayers have been produced. These tubes demonstrate an enhanced fracture energy and a gradual mode of failure. Another area of advanced ceramics where the use of EPD makes sense are functionally graded materials (FGM) in which one tries to combine in one component high hardness and high toughness. EPD allows the formation of FGM by depositing from a powder suspension to which a second suspension is continuously added during the process. An example will be shown of a graded WC-Co hardmetal. Introduction Many ceramics are used in the form of laminates especially functional ceramics in capacitors, sensors, microelectronic devices and others. From the mechanical properties point of view laminates are of interest because one may create ceramics with a threshold bending strength by introducing compressive residual stresses in those surfaces that will be subject to tensile loads in service [1]. Laminates may also be used to increase the toughness by alternating strong and weak layers. The role of the weak layers is to deflect cracks so that sudden catastrophic failure of the ceramic can be avoided [2]. These laminates are cheaper alternatives to fibre toughened ceramic composites. The stringent requirements of aerospace technologies have given rise to the development of composite structures in which one tries to combine the strong points of two materials and to realize in the same component often irreconcilable material properties such as for instance hardness and toughness. In the simplest of cases, these composite structures are layered systems, e.g. coatings. A well-known example is that of coating a tough substrate by a hard film. The resulting component combines the high hardness of its surface with the high toughness of its core. However, the sharp interface between both is subject to stress concentrations which may lead to delamination or spallation. These problems have inspired the concept of functionally gradient materials (FGM), in which harmful stress concentrations can be reduced by providing a gradual transition in microstructure between the two dissimilar materials. FGM’s [3,4] are thus distinguished from isotropic materials by gradients of composition, phase distribution, porosity, texture, and concomitant properties (hardness, density, resistance, thermal conductivity, elastic modulus, etc.). Those gradients are engineered and quantitatively controlled in order to achieve an overall improvement of the final component. In a similar way as in laminates a properly designed gradient Advances in Science and Technology Vol. 45 (2006) pp. 1075-1084 online at http://www.scientific.net © (2006) Trans Tech Publications, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 134.58.253.113-03/10/06,10:05:30)