COMPUTER-SIMULATIONS OF THE DYNAMICS OF SPINODAL DECOMPOSITION IN ALLOYS

Based on a numerical version of the Fourier transformation approach to the nonlinear Cahn-Hilliard diffusion equation, computer simulations of the dynamics of spinodal decomposition for a model alloy are carrie d out. The present simulations start from fluctuations in composition with small amplitudes and wavelengths (a few lattice spacings). This v ersion predicts that the Cahn-Hilliard equation has only weak nonlinea r character. The evolution of the composition profile and the dynamica l wave-number selection of the modulated structure are studied. The wa velength modulation of the composition profile occurs strongly in the early stage and becomes much weaker in the later stage. This selection has a strong dependence on both the mobility of solute atoms and the coefficient of the gradient energy. The kinetic evolution of the modul ated structure with time is investigated as a function of the composit ion, the mobility of solute atoms and the coefficient of the gradient energy. A critical comparison of the simulated results with prediction s of the linearized Cahn-Hilliard theory is presented.