Time evolution of a quenched binary alloy. IV. Computer simulation of a three-dimensional model system

We present results of computer simulations of the time evolution of a model binary alloy following quenching. Our model system is a simple cubic lattice each site of which is occupied by either an A or a B atom. There is a nearest-neighbor interaction which favors segregation into an A-rich and a B-rich phase at a point inside the two-phase region. Starting from a random configuration the system is quenched to and evolves at a finite temperature T as exchanges between atoms on nearest-neighbor sites are allowed to take place. In our present study, a lattice having a 20% concentration of A atoms (n̄A=0.20), was quenched to temperatures T=0.6Tc and T=0.9Tc, inside the two-phase region, and to T=1.1Tc. We study the evolution of the spherically averaged structure function $S(k,t)$, the energy, and various cluster properties, and compare our results with relevant theoretical predictions. We also compare the late time cluster distributions of small clusters for T=0.6Tc and T=0.9Tc with the equilibrium cluster distributions for corresponding temperatures on the coexistence curve (namely, n̄A=0.0146 at T=0.6Tc, and n̄A=0.1272 at T=0.9Tc). This shows that the phase segregation at T=0.6Tc takes place in two distinct stages (i) a "rapid" condensation of the A atoms into "liquid" drops and a "gas" phase consisting of monomers, dimers, etc., and (ii) a "slow" growth of the droplets. At T=0.9Tc (which is well inside the "classical" metastable region) such a segregation still seems to take place but at a slower rate.