Generalized Self-Organization of Alloy Microstructure Induced by Irradiation

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. Here we extend these studies to self-organization reactions that include both grain interiors and grain boundaries (GBs), and consider their impact on mechanical properties. We introduce two types of phase-field models to investigate this coupled self-organization in phase-separating A-B alloys. In a first model, an existing multi-order parameter phase-field model for polycrystalline alloys near thermodynamic equilibrium, thus including thermal segregation, is extended to the case of materials subjected to irradiation by adding a finite-range gaussian ballistic mixing contribution. A second model considers GBs as arrays of dislocations, providing a detailed information on alloy systems where irradiation adds another contribution to GB solute segregation through the kinetic coupling of point defect and solute fluxes. These models make it possible to identify irradiation conditions promoting coupled CP, thus simultaneously inside grains and at GBs, as well as identifying steady states of the microstructure as a whole that do not simply reduce to the superposition of known steady states for grain interiors and GBs. We compare these predictions to experimental results of precipitate evolutions in Al-Sc and Al-Sb, and assess the impact of solute re-distribution and precipitation on the hardness of these materials.