Pre-stressed ceramics with hybrid structure of mullite and alumina

Abstract

Most ceramic materials are inherently low fracture toughness and show extremely limited plastic deformation, because their chemical bondings are ionic and covalent. Hence, improvements of toughness as well as the strength of ceramic materials are necessary for a broader range of application. In this research, we concentrated on increasing strength and toughness of ceramic materials by multilayer-ceramic composite method. Die-pressing and slip casting were our selected processes. Alumina and mullite were selected as the starting materials and the attrition mill was used to reduce the particle size of these powders. The compositions of A-21/KM102 specimens were varied from 0/100 to 100/0 wt%. They were prepared by ball mill mixing and sintered at temperature ranging from 1650-1700 degree celsius for 2 hours. The die pressed multi-layered specimens were almost broken after sintering. The slip cast multi-layered tube specimens were also broken by the residual stress caused by the difference of thermal expansions. As a result, we concluded that this kind of hybrid structure is not a good solution to get high strength ceramics. On the other hand, the composite with 40A/60M wt% ratio showed (1) a homogeneous microstructure (without abnormal grain growth), (2) a rather higher K[subscript 1C] of 4.4 MPa.m[superscript 1/2] and (3) a good bending strength of 282 MPa.