GRAIN BOUNDARY MOBILITY OF ALUMINA AS A FUNCTION OF VARYING DOPANT CONCENTRATIONS

An important microstructural feature of polycrystalline materials is grain size, since grain size and the respective area of grain boundaries often affect mechanical and functional properties. As such, grain growth plays a significant role in microstructural evolution during sintering of polycrystalline materials. One of the most studied ceramic materials is α-alumina (α- Al₂O₃), which has served as a paradigm for the study of grain growth and is important for technological applications.

Many studies showed that dopants and/or impurities can cause significant changes to the grain boundary mobility of materials. This can occur by equilibrium (Gibbsian) segregation of solutes to grain boundaries, which is driven by a reduction in grain boundary energy. The segregated solutes then induce solute-drag or solute acceleration, changing the grain boundary mobility and how the microstructure evolves. Alternatively, above the solubility limit, dopants and/or impurities can result in precipitation of secondary phases, which either reduce grain boundary mobility by Zener drag, or accelerate mobility by the formation of liquid phases.

In this study the grain size as a function of annealing time was used to extract the effective grain boundary mobility for undoped polycrystalline alumina and alumina doped with Cr. Cr is fully soluble in alumina, so the correlation between solute activity, solute adsorption, and solute-drag/acceleration can be characterized over a range of solute concentrations.