ELECTRON-MICROSCOPY OF TRANSFORMATION DISLOCATIONS AT INTERPHASE BOUNDARIES

The concept of structural units (SU's) developed in order to describe the atomic structures of twin boundary facets is also used for interphase boundary (IB) facets quasi-parallel to small near-coincident planar cells of the two adjacent lattices. These facets, which have their own SU's, are separated by transformation dislocations (TD's), the cores of which are often related to ledges having heights equal to several interplanar spacings. It is shown that the Somigliana dislocation (SD) concept is a good tool for the computation of elastic displacement fields of these TD's in anisotropic elasticity. Applications are presented concerning the following IB's observed in high-resolution transmission electron microscopy (HRTEM): Si/TiSi2, Si/CoSi2, and Ni3Al/Ni3Nb. The identification of the atomic rows around some TD's at Si/CoSi2 and Ni3Al/Ni3Nb has been obtained by careful comparisons of experimental and calculated images.