Transmission electron microscopy of Suzuki segregation in fcc alloys

Transmission electron microscopy (TEM) observations concerning the temperature variation of the width of dissociated dislocations in fcc alloys have been reviewed with special reference to the segregation of solute atoms to the dissociated dislocations. Results of in-situ annealing in a high voltage electron microscope as well as a bulk annealing experiment have shown that noble-metal - base alloys can be divided into two groups: one group with solutes belonging to the IIIb group of the periodic table does not show any positive evidence for the Suzuki segregation, while the other group with solutes belonging to the IVb and Vb groups shows definitive evidence for the Suzuki segregation. This apparent difference in the segregation behaviour can be rationalized by a difference in atomic diffusivity of different solute atoms in these alloys; solute atoms belonging to the IVb or Vb group migrate much faster than those belonging to the IIIb group because of a large binding energy of vacancy-solute pairs. During irradiation by 1 MeV electrons, radiation-induced non-equilibrium segregation has been observed in Ag-Al, Ag-In, Cu-Si and Cu-Ge alloys. Mechanisms for the radiation-induced segregation are also discussed in terms of a large binding energy of vacancy-solute pairs for those alloys that contain IVb or Vb solutes. (author)