SELF-DIFFUSION MECHANISM IN NI-BASED L1(2) TYPE INTERMETALLIC COMPOUNDS

We propose a model for the self-diffusion in Ll(2) type A(3)B ordered compounds. In this structure, the atoms of the major element A can dif fuse on their own sublattice (alpha sublattice) via the ordinary vacan cy mechanism without disturbing the ordered arrangement. For the atoms of the minor element B, the same mechanism is possible for those dist ributed over the alpha sublattice as antisite atoms. If the number of the antisite atoms is not negligibly small, the long-range diffusion o f B can be due largely to their migration over the alpha sublattice as impurity diffusion. The self-diffusion data in Ni3Al, Ni3Ga and Ni3Ge are discussed in the light of this model.