INFLUENCE OF MODULATED STRUCTURES ON ORDERING DYNAMICS IN CUAU

Using a microscopic model, we have studied the evolution of microstruc ture in a model metallic alloy. The Hamiltonian was derived from the e ffective medium theory of cohesion in metals (EMT): an approximation s cheme for integrating out the electronic degrees of freedom and constr ucting an effective classical Hamiltonian. The alloy chosen for this s tudy was CuAu which exhibits a sequence of first-order phase transitio ns: disordered --> modulated --> ordered. To describe the dynamics of ordering, a free energy functional was constructed from the EMT Hamilt onian and used in a Langevin equation. This study demonstrates the fea sibility of predicting microstructure in alloys starting from a descri ption based on the electronic structure of alloys. The simulations exh ibit interesting features in late-stage growth which are attributed to the presence of the modulated phase as a metastable phase in the orde red regime.