Atomic transport mechanisms in irradiated copper(3)-gold alloy

The properties of radiation-induced defects were investigated by examining the radiation-enhanced diffusion and radiation-induced order-disorder kinetics in the ordered intermetallic alloy Cu$\sb3$Au.Direct measurements of thermal and radiation-enhanced diffusion on MBE grown Cu$\sb3$Au films were performed for the first time both above and below the order-disorder transition temperature. Ni and Pd impurity tracers were employed to simulate the diffusion of Cu and Au respectively. Activation enthalpies of diffusion were obtained for the two tracers above and below the ordering temperature. Both diffusion coefficients were found to decrease significantly on ordering, by factors of two and four for thermal and radiation-enhanced diffusion respectively. The results indicate that interstitial atoms do not contribute to atomic transport in irradiated Cu$\sb3$Au.Radiation-induced order-disorder was studied under He and Ne irradiation. At low temperatures, T $\le$ 250$\sp\circ$C, the order parameter, S, decayed exponentially with fluence owing to atomic mixing in displacement cascades. At high temperatures, T $\ge$ 300$\sp\circ$C, S quickly reached a steady state indicating a dynamic balance between ordering and disordering processes. The studies revealed the surprising result that the rate of disordering increases strongly with temperature near the transition temperature and that this was due to disordering by vacancy fluxes to sinks.Recovery of order in irradiated and unirradiated systems was also investigated. From measurements of reordering rates in the irradiated and unirradiated system, the defect concentrations in Cu$\sb3$Au under the He irradiations were obtained for the first time. The results revealed that the vacancy concentration is ${\sim}10\sp{-9}$ and the interstitial concentration is ${\sim}10\sp{-4}$. The results also suggests that interstitials are clustered and immobile, explaining why they do not contribute to the diffusion process. Using measured defect concentrations from the ordering experiments, D$\sb{\rm RED}$ could be predicted to within a factor of three of the measured values.U of I OnlyETDs are only available to UIUC Users without author permissio