TABLE OF CONTENTS Layered-graded materials (LGMs) exhibit a stepwise or progressive change in composition, structure, and properties as a function of position within the material [Koizumi, 1993; Hirai, 1996]. This innovative design eliminates ever-present sharp boundaries in conventional composites which may impart undesirable physical and mechanical properties. An example is debonding or separation at the boundary due to thermal or residual stress induced by mismatch in thermal expansion. LGMs have been processed by a variety of methods. A list of the common synthesis methods & examples of these materials have been described elsewhere [Sakai & Hirai, 1991]. Recently, liquid infiltration of preforms [Marple & Green, 1990; Low, 1998a] has emerged as an innovative technique for the processing of graded composite materials. Using this infiltration process, it is possible to design new materials with unique microstructures (e.g. graded, multiphase, microporous, etc.) and unique thermomechanical properties (e.g. graded functions, designed residual strains, thermal shock, etc.).
Recent developments in layered ceramics have provided a strategy for laminating the ceramic structure with an outermost homogeneous layer to provide wear resistance and an underlying heterogeneous layer to provide toughness [An et al., 1996; Liu et al., 1996; Padture et al., 1995]. These layered structures promote toughness by interlayer crack...
