The study of kinetics of the order-disorder phase transition in CuAu is performed in the framework of the time-dependent Ginzburg-Landau theory. The analytical solution for the motion parameters of the interphase boundary is applied to the calculations of width and velocity at different overheating and overcooling temperatures. We propose a way of verification of validity of the mean-field approach for order-disorder phase transitions. Cu-Au alloys represent almost all wide spectra of

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... of alloys, including orderdisorder phase transitions, formation of modulated structures, absence of missibility gap, dependence of ordering on the vacancies concentration in an alloy, etc. [l-71. This system appears to be a testing one for different approaches and models, that are aimed to describe phase relations in alloys. The most straightforward model for ab initio calculations is based on the Ising model with parameters obtained from first-principles band structure calculations [8-101. The Monte Carlo simulations and the cluster variation method describe the main features of the equilibrium phase diagram in a proper way. At the same time the improvement of the statistical model does not help if one wishes to test the theory on more delicated properties of Cu-Au alloys, such as formation of modulated structures or distortions of the lattice appearing in the ordering transitions. In Ref. [I] it was shown that the Landau theory derived from an alloy Hamiltonian based on the semiempirical non-self-consistent approach of cohesion in solids provides a good description of the order-disorder transformation for CuAu, CusAu and CuAu3. The achievement of the Landau theory carried out in Ref. [I] is the prediction of a modulated CuAuII structure in the temperature range between CuAuI and disordered phase. Thus it was demonstrated that even within the mean-field approximation all main aspects of the phase diagram may be captured. At the same time it was shown in Ref. [I] that the CuAuI phase appears through a diffusionless first-order transition. In addition to the results obtained in the framework of this approach which show its efficiency we would like to suggest in this paper a direct experiment which may settle the Article published online by EDP Sciences and available at http://dx.