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The deformation modes of single crystal NiAl deformed in compression in the range 77 to 1000 O K were found to be dependent on orientation and temperature. The preferred slip direction was confirmed as (OOl), but this may be constrained geometrically to allow kinking, or slip in (111) or (011) directions, depending on temperature. When (001) slip occurred, the slip plane was invariably { 110) at 77 O K but was dependent on orientation a t higher temperatures. The slip planes were also sensitive to temperature when slip occurred in other directions. The von Mises criterion for polycrystalline ductility can be satisfied by combinations of the observed slip systems.On trouvb que le mode de dbformation de monocristaux NiAl, deformbs par compression entre 77 et 1000 O K depend de l'orientation ainsi que de la tempbrature. On confirme que la direction pdferentielle de gliasement est

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The mobility of dislocations in ionic crystals has been shown directly to determine many of their mechanical properties. In turn this mobility is determined by the interactions between moving dislocations and the crystal lattice through which they move. These interactions include that which is inherent in the periodic nature of the lattice, i.e., the Peierls force, and those with defects and with impurity ions present in the lattice. The density and distribution of impurity-vacancy dipoles, and, in particular, their relaxation times and state of aggregation, are important in determining the nature of the interaction, and its magnitude, and these factors have been studied experimentally with a wide range of physical techniques in a number of ionic alloy systems. The results indicate that the elastic interaction between dislocations and the tetragonal strain field of the dipoles is important in determining the dislocation mobility.