Grain Boundaries in Iron

Abstract

Knowledge of grain boundary properties is crucial for many applications in materials science. In this entry, we summarize fundamentals of grain boundary structure and segregation with focus onto their relationship. First, a full description of the grain boundaries is given considering individual degrees of freedom, as well as some models for classification of grain boundaries. Grain boundary segregation is described on the basis of Langmuir–McLean approach that deals with the thermodynamic parameters of segregation that can be used for further generalization in calculations and prediction. In this respect, some interesting consequences of anisotropy of grain boundary segregation are illustrated, such as grain boundary segregation diagram and enthalpy–entropy compensation effect, both of which can serve for the prediction of thermodynamic parameters of grain boundary segregation in bcc iron and steels. A relationship between grain boundary chemistry and mechanical properties such as Hall–Petch relation and temper embrittlement is also briefly outlined.