Properties Related Phase Evolution in Multilayer Silicate Ceramics

Abstract

The use of ceramic processes inducing a microstructural organization at the grain scale favors the improvement of strength and toughness. With layered structures, it is possible to design the microstructural characteristics of materials, leading to increased threshold strength. Layered structures can be arranged to control the local residual stresses causing elastic mismatches between dissimilar materials and crack deflection at interfaces. In this way, multilayer composites from kaolinite and alumina or mullite fibers were shaped by tape casting and staked by thermo-compression, or by centrifugation. During sintering, they show at strong anisotropic behavior, which is in correlation with different activation energy for sintering. Mullite growth is also anisotropic, inducing the formation of an organized micro composite microstructure. The mechanical and elastic properties are correlated with the organization degree of mullite crystals, due to the formation of an interconnected mullite network in the microstructure. It is also shown that variations of mechanical and elastic properties are correlated with the texture index obtained by Quantitative Texture Analysis from X-ray data. The anisotropy of the elastic properties is evidenced by different values of Young’s modulus in directions parallel and perpendicular to the casting direction. Beside, the crack growth resistance is governed by discontinuities along layer boundaries and fiber interfaces.