The monitoring of grain-boundary grooves in alumina

The geometry of grain-boundary grooves in polycrystalline alumina has been studied using a combination of visible-light microscopy (VLM) and atomic force microscopy (AFM). Samples were heat treated in air to induce thermal grooving. A VLM map was made from the central region of each sample. Profiles of grooves located within the VLM maps were measured using AFM. Using again VLM maps, the same regions were re-examined using AFM after an additional heat treatment. This approach allowed the geometries of grooves which formed at migrating grain boundaries to be directly compared with those at stationary boundaries. The groove profiles measured were asymmetric at migrating grain boundaries and more nearly symmetric at stationary grain boundaries.