Influence of modulated structures on ordering dynamics in CuAu

Using a microscopic model, we have studied the evolution of microstructure in a model metallic alloy. The Hamiltonian was derived from the effective medium theory of cohesion in metals (EMT): an approximation scheme for integrating out the electronic degrees of freedom and constructing an effective classical Hamiltonian. The alloy chosen for this study was CuAu which exhibits a sequence of first-order phase transitions: disordered → modulated → ordered. To describe the dynamics of ordering, a free energy functional was constructed from the EMT Hamiltonian and used in a Langevin equation. This study demonstrates the feasibility of predicting microstructure in alloys starting from a description based on the electronic structure of alloys. The simulations exhibit interesting features in late-stage growth which are attributed to the presence of the modulated phase as a metastable phase in the ordered regime.