Phase transformations under irradiation

Abstract

Introductory examples of phase tranformations under particle irradiation illustrate the topic of the lecture. Basic mechanisms for radiation-induced diffusive phase transformations are the ballistic transport and radiation-enhanced diffusion. Quantitative information about ballistic transport comes from depth profiling of layer samples irradiated by ions. The characteristics of radiation-enhanced diffusion are described by looking at the results for impurity and self-diffusion in Cu and two Fe-Cr-Ni alloys. Radiation-induced segregation operating in the majority of alloys often leads to spatially inhomogeneous phase transformations. The fundamentals of the inverse Kirkendall effect are explained and results are demonstrated for a number of examples. The respective effect of migration and sink annihilation of solute-defect complexes is discussed for a few examples. The size evolution of second phase precipitates is discussed by means of a simple model which points out the significance of the counteraction of ballistic transport and radiation-enhanced diffusion. As a result, the importance of the cascade size and the lack of knowledge on the composition profile near the phase interface are emphasized. For the radiation-induced order-disorder transformation, the fruitful use of results from molecular dynamics calculations for experiment evaluation is demonstrated by discussing the dependence of the degree of long-range order on the fluence.