Radiation-induced segregation in metals

Abstract

During fast-particle irradiation significant fluxes of point defects can be set up adjacent to sinks such as surfaces or internal grain boundaries. In general, the different atomic species in an alloy move at different rates in response to these point-defect fluxes so that some species move towards sinks while others move away. This radiation-induced segregation causes significant changes in the local composition near sinks such as grain boundaries, and this can have important implications for the bulk properties of materials. In recent years this has been studied in some detail, particularly in structural materials used in nuclear reactor components. This paper describes recent advances in experimental techniques which have improved our understanding of radiation-induced segregation. The experimental evidence for the various different mechanisms for solute segregation are discussed, particularly for the cases of dilute and concentrated alloys. The role of accelerator-based experiments on high-purity model alloys is emphasised and the problems of understanding the behaviour in more complex alloys and steels is highlighted. Theoretical models for radiation-induced segregation behaviour in both dilute and concentrated alloys are reviewed, and their success in describing experimental data discussed. In the case of dilute alloys the work of Lidiard and co-workers on the kinetic theory of diffusion in dilute alloys has provided a firm theoretical foundation for the model of irradiation-induced segregation. Lastly, the directions for further work are indicated, including the need for a greater understanding of the role of interstitial point defects.