SELF-DIFFUSION AND INTERDIFFUSION IN INTERMETALLIC COMPOUNDS

Recent studies on self-diffusion in L1(2)-type intermetallic compounds and interdiffusion in intermetallic compounds of a Ti-Al system are r eviewed. In Ni3Ge compounds, the Ni diffusivity is two orders of magni tude higher than the Ge diffusivity; the major element diffuses faster than the minor element in L1(2)-type compounds. This trend is consist ent with the expectation based on the geometrical arrangement of Ni an d 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 diffusio n 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 diffus ion experiments; the latter involves extrinsic effects such as grain b oundary diffusion. The interdiffusion in TiAl and Ti3Al compounds is d iscussed with the self-diffusivities in terms of the Darken relation. (C) 1997 Elsevier Science S.A.