Caught in the act: Grain-switching and quadrijunction formation in annealed aluminum

Contrary to current understanding, an apparently stable single-phase quadrijunction, and one lacking any low-energy grain boundary member, has been experimentally observed during grain switching in large (∼mm) grained pure annealed aluminum. Electropolishing below the quadrijunction revealed a 3-D microstructure characterized by a rapidly shrinking grain with a faceted boundary indicating a significant anisotropy of energy and/or mobility. This unusual occurrence is described in detail in the expectation that a reasonable model for this observation might be found.

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