CONTROL OF TEXTURE IN MONOLITHIC ALUMINA

Conventional ceramic powder slips seeded with alpha-Al2O3 platelets were theologically processed to align the seed crystals. An aqueous-based gel reaction was used to ensure that alignment was retained in the green body and throughout the drying procedure. Bulk samples were produced by laying-up the cast tapes, filter pressing to form a green compact and then drying and sintering. The degree of preferred orientation in the sintered samples was characterized by X-ray diffraction. It was found that the degree of texture was significantly enhanced relative to samples processed in the same manner, but with no platelet additions. A scanning electron microscopic study of the final microstructures showed that the grain size and grain morphology were sensitive to the initial distribution of platelets within the green tape, which in turn was dependent on the volume fraction and size of the platelets. Further, it was demonstrated that using this technique it is possible to achieve a specimen which exhibits an equi-axed grain structure and yet has a strong degree of preferred orientation. Finally, studies of indentation cracking showed that a pronounced texture inhibited long-range crack propagation, and instead promoted localized cracking.