MICROSCOPIC MODEL FOR DIRECTIONAL COARSENING OF PRECIPITATES IN ALLOYS UNDER EXTERNAL LOAD

We carried out computer simulations of a binary alloy decomposition in two dimensions under external stress using a Metropolis exchange dyna mics with an effective long-range, anisotropic, ''spin'' Hamiltonian. This was obtained by minimizing the energy of elastic interactions bet ween A and B atoms of unequal size, over the displacement of atoms fro m the equilibrium lattice sites. The evolution of configurations and t he elastic strains associated with them were studied for Various initi al states. Directional coarsening was clearly visible in the precipita te morphology and was measured quantitatively both in the structure fu nction and in the amount of interface pointing in the x or y direction . These were found to saturate at a fixed ratio, independent of the in itial configuration: be it disordered or consisting of perfect stripes . This is due to an apparently inherent ''waviness'' of the precipitat e interfaces. A suitably defined mean domain size increases with time in a manner consistent with a t(2) behavior, with oc between 1/4 and 1 /3. (C) 1997 Acta Metallurgica Inc.