Self-diffusion and interdiffusion in intermetallic compounds

Recent studies on self-diffusion in L12-type intermetallic compounds and interdiffusion in intermetallic compounds of a Ti–Al system are reviewed. In Ni3Ge compounds, the Ni diffusivity is two orders of magnitude higher than the Ge diffusivity; the major element diffuses faster than the minor element in L12-type compounds. This trend is consistent with the expectation based on the geometrical arrangement of Ni and Ge in Ni3Ge. However, in Ni3Ga compounds, the Ni diffusivity is only 1.1–2.1 times larger than the Ga diffusivity in the temperature range 943–1112 K. This is explained by a mechanism of anti-site Ga diffusion in the Ni-sublattice in Ni3Ga compounds. Single-phase interdiffusion experiments are the most suitable to determine the interdiffusivity, which is much different from the data from multi-phase reaction diffusion experiments; the latter involves extrinsic effects such as grain boundary diffusion. The interdiffusion in TiAl and Ti3Al compounds is discussed with the self-diffusivities in terms of the Darken relation.