Thermodynamics of Grain Boundary Segregation and Applications to Anisotropy, Compensation Effect and Prediction

Quantitative AES at Interfaces

“…Moreover, AES data measured in different samples (for example, annealed at various temperatures) reflect the behavior of different grain boundaries. Such data should be neither compared nor used to determine thermodynamic characteristics of grain boundary segregation (enthalpy and entropy) because such values are "effective" without physical meaning [3,15]. Similarly, temperature dependence of average grain boundary concentrations measured in differently concentrated M-I alloys (item (ii)) provides us with effective values of segregation enthalpy and entropy (e.g.…”

“…This ratio technique is very useful, however, its interpretation has to be done correctly (e.g. [3,8]). A serious problem with application of the data on grain boundary segregation may also occur when the AES results are incorrectly treated.…”

“…This is frequently done when the data are averaged (i) over the total segregation depth; (ii) for differently concentrated M-I alloys; and (iii) for various interfaces/sites (i.e. neglecting the anisotropy of interfacial segregation) [3]. Probably the latter case is the most frequent one because grain boundary segregation is usually measured at various non-specified boundary facets of a polycrystalline material and thus, these data do not characterize any single interface.…”

“…Let us suppose that the segregated layer at the grain boundary is monatomic of thickness δ and that the fracture opening the boundary for AES and FS 2 denote the fracture surfaces after fracture, and the thick drawn line marks the fracture path, Θ 1 is the total area of FS 1 [3,8].…”

“…The values of the thermodynamic parameters of interfacial segregation are very important for generalization of segregation data and their further application for predictive purposes [3]. The crucial condition to obtain reliable values of the segregation enthalpy and entropy is careful measurement and quantification of the grain boundary composition, X I Φ , corresponding to chosen temperatures.…”