22 - Functionally graded ceramics

Abstract

Functionally Graded Materials (FGMs) are multifunctional materials that contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. In the ceramics composites field, a wide range of functionally graded ceramics is available. The gradient composition in FGMs not only results in a spatial variation in properties but also generate residual stresses, which affect the mechanical properties. One of the potential advantages of FG components is the positive influence of compressive residual surface stresses on the strength and wear resistance. A widely used technique for ceramic/ceramic gradient materials is sequential slip casting where slips of different compositions are cast one after and over another. In metal/ceramic FGMs with a continuous metal phase and a discontinuous ceramic phase, the sintering rates are controlled by the densification of the metal phase and such FGMs can be densified by conventional sintering methods. In most FGMs where high ceramic phase content is envisaged, however, some special approaches have to be considered for full densification.