Initial stage of bi-modal microstructure in TiO2-doped α-Al2O3 ceramics induced by SiO2 impurity

Abstract

Abstract Uni-modal and bi-modal microstructures were concurrently observed in a TiO2-doped -Al2O3 ceramic material with some SiO2 impurity. The segregation of Ti and Si to grain boundaries was systematically evaluated to reveal their role at the start of anisotropic grain growth. In general, in the bi-modal area grain boundaries exhibit higher Si excess than those in the uni-modal area. However, the basal plane of anisotropic grains was always found to contain more segregated Si while the non-basal planes were found to contain less Si. Such enrichment of SiO2 was also found at the basal planes of equiaxed grains in the uni-modal area, which occurred in the initial stage of anisotropic grain growth. Before and after this stage, the grain boundary composition was relatively uniform with the mole ratio of SiO2 to TiO2 as 2.3: 1 and 5.8: 1, respectively. The latter should be related to the composition of eutectic liquid formed during the sintering, which is responsible for the development of the bi-modal microstructure.