Effect of grain boundary orientation on radiation-induced segregation in a Fe–15.2 at.% Cr alloy

Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, such as higher thermal fatigue resistance, lower thermal expansion coefficients and reduced swelling. However radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries in these materials is a concern because these phenomena could adversely affect their mechanical properties. In an effort to develop a full mechanistic understanding of RIS/RID, a systematic approach combining orientation imaging, site-specific specimen preparation and three-dimensional atomic-scale analysis has been developed to characterize the behaviour of Cr and C at grain boundaries during irradiation. This methodology has been applied to a Fe–15.2 at.% Cr alloy to investigate the effects of grain boundary misorientation, irradiation depth and impurities. Systematic differences in Cr segregation are reported as a function of grain boundary character and irradiation conditions. The similar properties demonstrated by grain boundaries of similar type means that it should be possible to apply relatively simple models to predict the long-term behaviour of these materials under irradiation conditions.