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CTION In an earlier paper appearing in this journal,[1] we pointed out that the incidence of Kirkendall Effect during single-phase interdiffusion in intermetallic compounds is not consistent with those unit processes of diffusion which conserve the lattice sites at the end of the unit diffusion process. The concerned unit diffusion processes are six-jump vacancy cycle (SJVC),[2,3] tripledefect mechanism (TDM),[4] and antistructure bridge (ASB) mechanism.[5] In the preceding article, Belova and Murch (BM) contested our thesis and suggested that our arguments are based on improper understanding of the basic tenets of the theory of solid state diffusion and finer nuances of the three diffusion processes mentioned above. We find ourselves unable to agree with the hypothesis and line of arguments adopted by BM to negate our thesis forming the basis of our paper under consideration. We begin our reply to BM’s contribution by first discussing the two very important issues forming part of our paper which have been completely ignored by BM in their contribution. This will be followed by our responses to the specific issues raised by BM.

G.P. TIWARI, Professor, is with the Ramrao Adik Institute of Technology, Vidya Nagri, Nerul, Navi Mumbai 400703, India. Contact e-mail: [email protected] R.S. MEHROTRA, Consultant, is with the C-18, Rohini CHS, Sector 9A, Vashi, Navi Mumbai 400703, India. Manuscript submitted June 25, 2013. Article published online July 31, 2013 4422—VOLUME 44A, OCTOBER 2013

ROLE OF NONCONSERVATION OF LATTICE SITES IN THE OCCURRENCE OF KIRKENDALL EFFECT The basis of our paper under consideration is the fact that whenever the Kirkendall effect is manifested in the course of single-phase interdiffusion, admissible diffusion mechanisms are only those which do not conserve the lattice sites at the end of elementary diffusion cycle. SJVC and TDM as well as ASB (in the format currently conceptualized) do not meet this criterion. It is on these grounds that we concluded that all three of them may not have a significant role during single-phase interdiffusion and, by extension of the same logic, in the selfdiffusion of homogenous intermetallic compounds as well. For instance, if the conventional monovacancy migration is the operative mode of self-diffusion in copper and nickel, it is expected that the same mode of diffusion will prevail in the course of interdiffusion in the copper-nickel system. We have based our proposition on Seitz’s hypothesis[6] that the Kirkendall effect, which is concerned with the motion of fiducial markers during diffusion, excludes a direct exchange mechanism as the major contributing factor. We quote below from his paper: The Kirkendall Effect cannot be explained naturally in terms of the diffusion mechanism if this is assumed to be exclusively of the interchange type, that is, if one of the possible mechanisms studied by Zener[7] is assumed to predominate completely. For in this case an atom which shifts its position would always do so by moving from one normal position to another and would always be