Embrittlement of interfaces by solute segregation

We discuss theoretical models of interfacial embrittlement by solute segregation. Of properties susceptible to alteration by segregation, the ideal work of interfacial separation, 2γ int, is predicted to have an important but probably not exclusive role in controlling embrittlement. A thermodynamic framework for estimating 2γ int from data available through free surface and grain boundary adsorption studies is outlined, and relevant segregation energies are given for carbon, phosphorus, tin, antimony and sulphur segregation in iron. Data from intergranular fracture experiments involving these same segregants is also summarized in an attempt to test the idea that segregation-induced embrittlement (or ductilization) can be understood in terms of the segregant's effect on 2γ int. Uncertainties in present data do not allow a convincing test, but it is not implausible that the deleterious effects of phosphorus, tin, and sulphur in iron can be understood in this way. The effect of carbon does not seem to be similarly understandable, although that may be due to the inappropriateness of the only available surface segregation data in that case, which are for a (001) surface rather than a general polycrystalline surface created by intergranular fracture.