Boron segregation in intermetallics: on the possible origins of a low-level intergranular segregation

摘要

Boron segregation to the grain boundaries in intermetallics represents an important phenomenon, as it strongly reinforces these alloys which are at room temperature intergranularly brittle when pure. Low level of grain boundary saturation by the solute element is one of characteristics of boron segregation in these materials; that is why theoretical description of the segregation phenomenon by the simple Langmuir-McLean segregation isotherm does not generally provide physically realistic correlation. In this work, two approaches to the correlation of experimental data on boron segregation at grain boundaries in intermetallics are discussed, taking into account different physical reasons of its low level, the Fowler segregation isotherm, and the Langmuir-McLean segregation isotherm considering grain boundary saturation. The capability of both approaches is documented for experimental data on boron segregation at grain boundaries in FeAl and Ni_3Al base intermetallics, provided by previous works. The correlation according to the Fowler isotherm requires an interaction parameter indicating strong repulsion of boron atoms. In the latter approach, the limited number of segregation positions is explained by interstitial nature of boron segregation and by a high degree of grain boundary order. It is shown that both approaches are simply and closely related.