Kinetics of irradiation-induced phase transformations in tricritical systems

We discuss the time evolution of local changes in the alloy composition (Formula presented) and in the degree of long-range order (Formula presented) under irradiation with energetic particles. Coupled kinetic equations for (Formula presented) and (Formula presented) are derived in the time-dependent Ginzburg-Landau forms, taking into account the irradiation-induced atomic mixing and disordering as well as the irradiation-enhanced diffusion and ordering. At first, we obtain the model phase diagrams of stationary states under appropriate conditions of irradiation. It is shown how the ordering phase field and the miscibility gap between ordered and disordered phases depend on the irradiation conditions. Next, we demonstrate some examples of the simulation of the dissolution process from the two-phase mixture of (order+disorder) into a single-phase state. At a relatively low temperature, the ordered phase is first disordered and then the composition modulation disappears by dissolution. In contrast, the disordering and the dissolution proceed simultaneously at higher temperatures.