Microstructural engineering of functionally graded materials by electrophoretic deposition

An important challenge in the design and processing of engineering materials is to combine irreconcilable properties of materials, such as hardness and toughness, in the same component. A possible concept to meet this demand is that of functionally graded materials (FGMs). The main feature of a graded material is the position-dependant composition and related mechanical properties. Electrophoretic deposition (EPD) is a fairly rapid low cost process, capable of producing such FGMs with complex geometry. This paper reports on processing of homogeneous as well as continuously graded ceramic–ceramic (ZrO2–Al2O3) and ceramic–metal composites (WC–Co) by means of EPD. The EPD characteristics of the constituent powders, such as the point of zero charge (pzc), the natural pH, the electrophoretic mobility, the effective particle charge and the resistance of the suspension are experimentally determined. The EPD processing parameters are described and the mechanical properties of the densified FGM composites are reported and evaluated. A model for the EPD process has been developed which enables to calculate the composition gradient in the FGM material from the starting composition of the suspensions, the EPD operating parameters and the powder-specific EPD characteristics.