Interphase and antiphase boundary stability in bcc compounds under irradiation

To model the behaviour under irradiation of a bcc alloy presenting the B2-A2 order-disorder transition, we propose a mean-field approximation of a kinetic model with two atomic exchange mechanisms acting in parallel: thermally activated and forced jumps. By integration of deterministic evolution equations, we show that irradiation can induce the stabilization of a two-phase alloy, while the classical equilibrium phase diagram only displays single-phase fields (the B2-A2 transition is second order). Steady-state diagrams are computed: in the two-phase region, surface tension-like effects are identified, antiphase boundaries are found to be unstable with respect to the disordered solid solution and smaller precipitates shrink to the benefit of the larger ones. Monte Carlo simulations confirm that the transition can become of first kind under irradiation and allow to study cascade size effects.