BERYLLIUM BI-CRYSTAL STUDIES. VOLUME II.

The object of this program has been to evaluate the role of grain boundaries in the deformation and fracture behavior of beryllium. Utilizing bi-crystals grown by a parallel seed-floating zone technique, selected orientation configurations believed significant in polycrystalline deformation have been investigated. Features of flow and fracture in bi-crystals deformed in direct tests to failure and companion interrupted tests have been examined by optical microscopy as well as surface replication electron microscopy. Dislocation interactions at the boundary have been evaluated by electron transmission microscopy of thin foils. Brittle behavior was noted in the asymmetric and modified symmetric configurations investigated. Inability to accommodate mixed dislocation interactions, and complex grain rotations are believed responsible. In the absence of these adverse circumstances in a symmetric configuration, ductile behavior was observed. Other potentially ductile symmetric configurations should be evaluated to further clarify features of polycrystalline deformation. Author