Grain-boundary structure direct observations

Fig. 10 High-resolution Z-contrast imaging. Z-contrast image of a grain boundary in SrTi03 (perovskite structure) recorded in 0 0 1 direction. One of the unit cells framed in the micrograph is illustrated on the left, the Sr columns (bright) are at the corner of the unit cell, in the center there is a TiO column. The pure oxygen columns, black in the model, are not observable in the Z-contrast image. The atomic number (Z) contrast is apparent with increasing atomic number (Z) of the elements, the intensity increases. (View this art in color at WWW. dekker. com.)...

The Portevin-Le Chatelier effect with serrated yielding was observed for both the ordered and disordered state (Mohamed etal., 1974). Recovery and recrystallization have been analyzed in detail (Vidoz etal., 1963 Cahn, 1990, 1991). Experimental and theoretical studies have been directed at dislocations and antiphase domain boundaries (see, e.g. Tichelaar and Schapink, 1991 D. G. Morris, 1992 Veyssiere, 1992), grain boundaries (Yan etal., 1992), and the electronic structure (Bose et al., 1991). It is noted that disordered layers are formed in ordered CujAu on antiphase boundaries and twin boundaries just below the order-disorder transition temperature (Tichelaar et al., 1992). This may be expected in other phases, too, and may improve the ductility of less ductile phases, as is discussed for NijAl (see Sec. 4.1.2). 

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