MODELING OF ORDER COMPOUNDS DURING IRRADI ATION - DYNAMIC EQUILIBRIUMDIAGRAMS AND MICROSTRUCTURAL EVOLUTION

To model the behaviour under irradiation of a B.C.C. alloy presenting the B2-A2 order-disorder transition, we propose a mean-field approxima tion of a kinetic model with two atomic exchange mechanisms acting in parallel: thermally activated and forced jumps. By integration of dete rministic evolution equations, we show that irradiation can induce the stabilization of a two-phase alloy, while the classical equilibrium p hase diagram only displays single phase fields (the B2-A2 transition i s second order). Steady-state diagrams are computed: in the two-phase region, antiphase boundaries are found to be unstable with respect to the disordered solid solution and smaller precipitates shrink to the b enefit of the larger ones. The different dissolution paths of B2 preci pitates are studied.