Interface structure and strain development during compression tests of Al2O3 / Nb/Al2O3 sandwiches

The interface structure of an Al2O3/Nb/ Al2O3 sandwich produced by solid-state diffusion bonding was investigated in detail by various transmission electron microscopy (TEM) methods. The joint possessed at one interface a (110)Nb jj (0001)Al2O3 , ½1 10 Nb jj ½2 1 10 Al2O3 , and on the other interface a (110)Nb jj ð0001ÞAl2O3 and [1 10]Nbjj½0 1 10 Al2O3 orientation relationship. At both interfaces, misfit dislocations formed to compensate the lattice mismatch as found by high-resolution transmission electron microscopy (HRTEM). Electron energy-loss near edge structure (ELNES) studies revealed that the interface is terminating with an Al layer resulting in Al–Nb bonds. Identical sandwiches were investigated on the meso- and macroscopic scale by performing compression tests and simultaneously monitoring the strain development at (001)Nb and ð1 10ÞNb crystal faces. The full-field optical strain measurements (FFOM) revealed that the strain is localized at the interfaces when observed at the (001)Nb face while it is along the maximum shear directions of 36–54 inclined to the interface when observed at the ð1 10Þ face. The strain localization along a specific maximum shear direction results in the cleavage of Al2O3, always initiating from the interface possessing the (110)Nb jj ð0001ÞAl2O3 and [1 10]Nb jj ½0 1 10 Al2O3 orientation relationship.