Auger electron spectroscopy has been extensively employed to investigate grain boundary segregation of impurities and alloying elements in polycrystalline materials. This method has provided interesting information on solute atoms segregated at grain boundaries by analyzing intergranular fracture planes. However, it has been recognized in previous work that experimental results on intergranular fracture planes cannot be simply interpreted by thermodynamic models, since the results include several factors which mainly arise from microstructures in polycrystalline materials. Recently the factors influencing the experimental results have been understood, owing to systematic studies of grain boundary segregation in polycrystalline high-purity iron base alloys and in iron-silicon bicrystals with various orientations. This overview reviews the experimental results obtained in these iron base alloys, and discusses characteristic features of grain boundary segregation of solute atoms, in particular the effects of grain boundary structure, annealing temperature and third elements on grain boundary segregation.
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