Single-phase interdiffusion studies in the B2 intermetallic compounds NiAl and FeAl have demonstrated the incidence of Kirkendall effect in these systems. The implication of this observation on the operating mode of self-diffusion in these systems is discussed. The direct exchange and ring diffusion mechanisms were excluded as the possible mode of substitutional diffusion in metals and alloys on account of the incidence of Kirkendall effect during single-phase interdiffusion studies. It is suggested that on similar phenomenological considerations, the six-jump vacancy cycle mechanism, triple-defect mechanism, and antistructure bridge mechanism are precluded as possible mode of diffusion in B2 intermetallic compounds.
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