REM-Untersuchung des Umlösungsvorgangs von γ6-Aus-scheidungen in Ni-14 at.% Al-Kristallen, speziell an Orten erhöhter Versetzungsdichte, an Subkorngrenzen und Gleitlinien

The splitting and dissociation behaviour of γ 6 -particles induced by appropriate heat treatment in Ni-14 at%-Al crystals with [100] normal to the surface, was investigated with optical and scanning electron microscopy, in particular in areas of increased dislocation density, i.e. subgrain boundaries and slip lines, but also for individual, isolated γ 6 -particles. The heat treatment was chosen so that the γ 6 -particles would only be fully developed in the subgrain boundaries and slip lines; the growth of the γ 6 -particles in the undisturbed crystal would just become visible. It has been shown that during coarsening the dissociation process and the splitting of the large particles in the γ 6 -chains in subgrain boundaries and slip lines almost always takes place along cubic planes. Splitting along (111) planes, the slip planes, which would mean a direct involvement of dislocations induced by deformation in the splitting process, could not be observed, apart from one exception mentioned. The stress fields in the γ/γ ' -microstructure could be revealed by repeated etching. The lattice distortions at a (100) surface of a crystal were etched with an etchant insensitive to the difference of γ and γ 6 . The matrix in the (100) direction was then removed in order to make the 7-particles in the etch pits visible. The centres of higher lattice distortion are not situated at the cube corners, but rather in the centres of the cube faces, where the splitting or cavity formation for the larger γ 6 -particles starts.