LATTICE IMAGING OF DISLOCATIONS AT THE GAMMA/GAMMA' INTERFACE IN DEFORMED NI-BASED SUPERALLOYS

The recent developments in High Resolution Transmission Electron Microscopy allow lattice imaging of defects in alloys. The present contribution shows how this technique can be used, together with weak-beam studies, in order to give pertinent and precise information about elementary mechanisms of shear of gamma' precipitates by matrix dislocations in an Ni-based superalloy. It reveals the nature and the spatial extension of the superlattice stacking fault that can be encountered in this family of composite alloys. Moreover, with the aid of lattice simulation, the physical nature of the bounding dislocations at the gamma/gamma's interface and not only the mathematical value of their Burgers vector can be found. The result is that shearing mechanisms can be proposed with a true physical meaning.