Anisotropic Grain Boundary Networks and Their Role in Abnormal Grain Growth

Current grain growth models have evolved to account for the relationship between grain boundary energy/mobility anisotropy and the five degrees of grain boundary character. However, the role of grain boundary networks on overall growth kinetics remains poorly understood. To experimentally investigate this problem, a highly textured Al₂O₃ was fabricated by colloidal casting in a strong magnetic field to engineer a unique spatial distribution of grain boundary character. Grain growth behavior was tracked and quantified via electron backscatter diffraction (EBSD) for the textured microstructure, as well as for an untextured control sample. A prevalence of (0001)/(0001) terminated grain boundaries with anisotropic networks were identified in the textured sample, which were determined to be facilitating grain growth at a faster rate than predicted by models. Additionally, although abnormal grain growth (AGG) was observed in the control sample, it was not observed in the textured microstructure. The underlying mechanisms of this unexpected behavior are explored by using atomic force microscopy (AFM) to quantify differences in the relative grain boundary energy within characteristic local networks of the textured and untextured microstructure. These findings will allow better modelling of grain growth in real polycrystalline systems by experimentally exploring the impact thereon of grain boundary plane anisotropy and relative energy/mobility differences between neighboring boundaries.