Interface Structure and Kinetics in Doped Alumina

Abstract

Grain boundaries in polycrystalline microstructures are often decorated with dopants that are added intentionally, or impurities that are acquired during processing and service. The nature of the foreign substances profoundly influences various materials properties including diffusional transport, interfacial fracture, oxidation, corrosion and creep resistance. In many metallic and ceramic systems interfaces with various types of segregation, from sub-monolayer to thick microscopic films, have been observed. Recently, these interface phases have been considered as thermodynamically distinct three dimensional phases, called Grain Boundary Complexions. In the current work, alumina has been chosen as a model system to study the various boundary complexion types and its relationship with boundary mobility. Grain growth kinetics measurements in hot pressed dense yttrium-doped and yttrium-silicon co-doped polycrystalline alumina showed boundary mobility varying over 6 orders of magnitude between 1200 °C and 2000 °C. Additionally, many different regimes of boundary mobility were observed. Microstructures corresponding to these distinct boundary mobility regimes were identified and quenched from the annealing temperatures to preserve the grain boundary structure. The presentation aims to focus on the relationship between the boundary mobility and the structural features of the interface complexions from complementary studies of electron microscopy and synchrotron XAFS.