The Emergence of Intergranular Precipitates in TiO2-Doped alpha-Al2O3 Ceramics
January 28, 2010
Volume 93 Issue 2, Pages 326 – 329
Pengxiang Qian, Hui Gu, Miaofang Chi Published Online: Nov 23 2009 6:57PM DOI: 10.1111/j.1551-2916.2009.03410.x
The minor phase accumulated at intergranular regions in ceramics is usually associated with the global doping level of additives; however, such simplification often undermines the local variation in liquid composition that leads to the emergence of precipitation. In this paper the correlation between precipitation and intergranular liquid was investigated in a TiO2-doped Al2O3 ceramic system. The discrepancy between XRD and SEM in detection of the intergranular Al2TiO5 phase was rationalized by their difference in sensitivity that corresponds to a change from the casual to general mode of local liquid variation. Analytical TEM in addition revealed Ti-rich nanoprecipitates aligning along grain boundary (GB). The two intergranular phases were associated with separate processes of intergranular liquid, as clarified via a representative case that exhibited the extra grain growth from annealing. The nanoprecipitates were created from a binary liquid in local equilibration with segregation to GB, which served as transporting routes to form ternary liquid at the multigrain junctions to initiate the main intergranular phase Al2TiO5.