MODELING SPINODAL DECOMPOSITION AT THE ATOMIC-SCALE - BEYOND THE CAHN-HILLIARD MODEL

In this paper three models are used to describe spinodal decomposition in Fe-Cr alloys. The challenge presented by this particular alloy sys tem is that the wavelength of the decomposition is at the nanometre sc ale. The scale of the microstructure is too small to expect the contin uum approximations of the Cahn-Hilliard approach to apply, and, indeed , we show that the approach fails to describe the kinetics of the expe rimentally observed decomposition. On the other hand it has already be en established in our earlier work that the dynamic Ising model descri bes the kinetics of this decomposition remarkably well. In this paper we show that the Penrose model of spinodal decomposition can also acco unt for the kinetics quantitatively. The Penrose model is deterministi c and is essentially a mean-field approximation to the dynamic Ising m odel. In addition we show that the form of the initial distribution of amplitudes of compositional variations within the high-temperature ra ndom alloy has a significant effect on the subsequent kinetics of phas e separation.