Abstract
Enhanced fracture toughness is provided for tri-layer SiC/AlN materials [1,2] with the compressive stress induced by the difference in the coefficient of thermal expansion (CTE) inside the outer layers. This suggests the possibility of applying the controlled CTE of the second-phase materials for toughening of ceramic-matrix composites. Celsians (MSi_2Al_2O_8, M: Ba, Sr / BAS and SAS) having the wide variety of CTE depending on the crystalline structure are promising materials for this purpose. However, pseudo-hexagonal BAS (α-BAS) transforms to its hexagonal polymorph (β-BAS) with the density decrement 3.296 to 3.267 g・cm^<-3>, resulting in the linear expansion 0.294% around 300℃. Then, the limitation of the expansion is required as well as the preparation of sinterable celsians with controlled CTE. In the present paper, the authors studied the sinterability, crystalline phase, and thermal expansion of solid-solutions in BAS-SAS and BAS-CaAl_2Si_2O_8 (BAS-CAS) systems. Applicability of the celsians as the reinforcements for α-Al_2O_3-matrix dispersion composites and as the components for multi-layered composites (MLCs) has also been examined.
