Novel precipitate structures in alloys under irradiation

Abstract

We investigate the fundamentals of precipitate stability under energetic particle irradiation, towards the goal of better controlling the microstructures of driven alloys. First we focus on an irradiation-induced precipitatewithin- precipitate structure, which is referred to as “cherry-pit” structure. We show by computer simulation and analytical modeling that the formation of cherry-pit structure is a special instance of compositional patterning, and that the conditions for compositional patterning and the formation of cherry-pit structures are related, but different from each other. Then we develop a new kinetic Monte Carlo model, which includes the generation, recombination, and sink elimination of irradiation-induced point defects, as well as ballistic mixing. With this tool we explore the possibility of using point-defect sinks to alter the temperature range where compositional patterns are stable. This novel approach for optimizing radiation-resistant materials is then tested experimentally using a Cu-Ag-W model alloy. Lastly we show that the addition of a high density of W nanoparticles dramatically alters the coarsening behavior of precipitate-hardened Cu-Ag alloys. First, the nanoparticles suppress precipitate growth, but far more surprisingly they induce non-equilibrium Ag wetting layers on grain boundaries. This observation is explained using kinetic Monte Carlo simulations, which show that caging of Ag precipitates by the W nanoparticles suppresses their growth and drives the formation of the wetting layers.