Entropy matters in grain boundary segregation

Abstract

Starting with a fairly comprehensive database on experimental results on enthalpy and entropy of grain boundary segregation, the detrimental influence of ignoring the segregation entropy term is shown for the latter as well as for additional examples of intergranular cohesion, the stability of nanograin size, and the segregation enthalpy-segregation entropy compensation effect. Furthermore, the decisive role of segregation entropy in the transition from substitutional to interstitial segregation with increasing temperature, and the newly explored effect of entropy-dominated grain boundary segregation are presented. Despite the direct evidence of the importance of entropy in grain boundary segregation, its contribution has been frequently neglected in the literature. One of the possible reasons is that the routines for a theoretical determination of the segregation entropy are still missing. We hope that, in the near future, progress in advanced theoretical methods will substantially improve our present understanding of grain boundary segregation.