Phase stability under irradiation in alloys with a positive heat of mixing: Effective thermodynamics description

The alteration of phase stability due to the continuous production Of force d atomic displacements, asis the case under irradiation, is studied. A simp le kinetic model of a binary alloy exhibiting phase separation is investiga ted, and two limiting cases are considered: nearest-neighbor ballistic exch anges and arbitrary-length ballistic exchanges. The model is simultaneously studied:by: direct kinetic Monte Carlo simulations, and by theoretical app roaches based in the description of the steady state by:effective thermodyn amics. Two theoretical frameworks are considered: a microscopic description bared in effective interactions, and a macroscopic description based in ef fective free energies constructed over a modified Cahn-Hilliard equation. D evelopments of these models are proposed to allow for quantitative predicti ons. For nearest-neighbor ballistic exchanges, the steady-state phase diagr am is evaluated for each of the approaches and the results are directly com pared. In the case of arbitrary-length ballistic exchanges, the appearance :of:labyrinthine mesoscopic structures at steady state is rationalized in t erms of the competition between short-range:attractive and long-range repul sive effective interactions. The favorable comparison between the theoretic al results and the direct Kinetic Monte Carlo simulations shows that the lo ng-term behavior of this inherently far-from-equilibrium system can be desc ribed in terms of effective thermodynamic potentials. [S0163-1829(99)05146- 2].