Dynamical Grain-Boundary Phase Diagrams in Irradiated Alloys

Past modeling and experiments have established that irradiation can induce the self-organization of phase-separating alloy systems into nanoscale compositional patterns (CP) owing to the competition between finite-range ballistic mixing and thermodynamically driven decomposition. We extend these results to self-organization reactions that include both grain interiors and grain boundaries (GBs). We introduce a phase-field model to investigate this coupled self-organization in model phase-separating A-B nanocrystalline alloys. GBs, described as arrays of dislocations, act as defect sinks where solute segregation and precipitation can take place owing to vacancy-induced solute drag. We show that this solute convection, even in the absence of ballistic mixing, can lead to arrested coarsening of GB precipitates. In the presence of ballistic mixing, GB precipitates can become global steady states thus extending the phenomenon of CP originally identified for grain interiors. Steady-state phase diagrams predicted by the model determine the irradiation parameters required for the stabilization of such nanostructures. These predictions are tested on Al-base and Ni-base alloys subjected to ion irradiation.