Choice of the Diffusion Interaction Mode

The first possibility is considered in the quasibinary system A—(Bi xCx) with limited solubility, but without intermediate phases. Analytical and numerical methods were used to find the solutions, which correspond to the case of a diffusion path going through the conode (at the interphase boundary, the concentrations jump between two edge points of the conode). At that the inter-diffusion in the couple A, solid solution (BC) was treated in the approximation of parabolic movement of the boundary. On the basis of diffusion equations for a and /3 phases and two equations for flux balance (for A and B components), one has 

The range of values for the parameters at which the system of differential equations has no solutions (negative concentrations are obtained) and thus diffusion without the two-phase zone is impossible, was found. Relying upon the results of 

At that boundary, the composition of the alloy BC shifts along the BC side. Indeed, if the intermetaUide requires different quantities of B and C, the initial alloy BC will become depleted of these components to a certain extent This, in particular, leads to homogeneity violation of the initial alloy of the BC couple, which in turn, causes fluxes in this part of the diffusion couple, and this influences the kinetics of the boundary movement When there are several intermediate phases on the phase diagram, the mentioned effect may cause competition between them. The failure of the two indicated modes may lead to the formation of the two-phase zone in the ternary system during the diffusion process the boundary concentration may appear to lie on different conodes and the diffusion path will not be able to bypass them. 

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