On the thermodynamic description of grain boundary segregation in polycrystals

Abstract

Thermodynamic parameters of grain boundary segregation have often been determined from the averaged data measured at fracture surfaces of polycrystalline materials by Auger electron spectroscopy. Owing to the presence of various non-specified grain boundaries at the fracture surfaces, the segregation enthalpies Δ H i o and entropies Δ S i o found in this way describe an averaged segregation behaviour and are not entirely physically well defined. In the present work recent measurements of grain boundary segregation of Si, P and C in well-characterized bicrystals of an α-Fe-based multicomponent alloy were used to determine the averaged segregation behaviour of model polycrystals. Results obtained for numerous model fracture surfaces are compared with both the actual segregation parameters of individual grain boundaries and the values of Δ H i o and Δ S i o found in the literature. On the basis of the application of Guttmann's theory of interfacial segregation to polycrystalline materials, the relationship between the segregation parameters of individual grain boundaries present at the model fracture surface and the averaged parameters is discussed.