We discuss theoretical models of interfacial embrittlement by solute segregation. Of properties susceptible to alteration by segregation, the ideal work of interfacial separation, 2 γ int , is predicted to have an important but probably not exclusive role in controlling embrittlement. A thermodynamic framework for estimating 2 γ 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 2 γ 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.

Embrittlement of interfaces by solute segregation

Failure of metals I : brittle and ductile fracture

Interfacial segregation and grain boundary embrittlement: An overview and critical assessment of experimental data and calculated results

Kinetics of non-equilibrium grain-boundary segregation

Effect of carbon on the grain boundary segregation of phosphorus in α-iron

The equilibrium grain-boundary segregation of phosphorus was investigated in Fe–P, Fe–C–P, Fe–Cr–P, and Fe–Cr–C–P alloys after annealing at temperatures in the range 400–800°C. The grain-boundary concentrations were determined by Auger electron spectroscopy on intergranular fracture surfaces. The phosphorus segregation in Fe–P alloys with 0·003–0·3%P can be described by the McLean equation, the free energy of segregation is ∆G° = −34 300–21·5T (J mol−1). The percentage of intergranular fracture is increased by the presence of phosphorus at grain boundaries. In Fe–C–P alloys grain-boundary segregation is affected by site competition. Increasing carbon content of the samples causes an increase of the carbon concentration and a decrease of the phosphorus concentration at the grain boundaries; the intergranular part of fracture is simultaneously lowered. The addition of chromium causes an increase of phosphorus segregation in Fe–C–P alloys but no change in Fe–P alloys. The behaviour in carbon-containi...

H. Erhart

Papers

Equilibrium segregation of phosphorus at grain boundaries of Fe–P, Fe–C–P, Fe–Cr–P, and Fe–Cr–C–P alloys