BETA-SIALON-SILICON NITRIDE MULTILAYERED COMPOSITES

Layered composites with alternating beta-SiAlON and silicon nitride la yers were fabricated using a tape-casting and laminating technique. A distinct layered structure was obtained by hot pressing, where composi tions of yttrium and aluminum at the layer interface were functionally graded in a thickness of similar to 10 mu m. A solid-solution reactio n prior to densification in the beta-SiAlON layer contributed to the c o-existence, in equilibrium, of these two layers, Density and Young's modulus depended on the volume fraction of silicon nitride layers acco rding to the rule of mixtures. The strength of the beta-SiAlON layer, estimated by an equivalent strain model, increased when compared to th at of the monolithic material, although the fracture origin always was observed within the beta-SiAlON layer. The layer thickness in an alte rnating layered configuration affected the strength of discrete layers .