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

One of the most dangerous technical failures of materials is intergranular brittle fracture (temper embrittlement) as it proceeds very quickly and its appearance is often hardly predictable. It is known that this phenomenon is closely related to the chemistry of grain boundaries and to the difference of the segregation energies of the grain boundaries and the free surfaces (Rice–Wang model). To elucidate the effect of individual solutes on embrittlement of various base materials such as steels and nickel-base superalloys, grain boundary and surface segregation was extensively studied in many laboratories. As a result, numerous data on surface and grain boundary segregation have been gathered in literature. They were obtained in two main ways, by computer simulations and from experiments. Consequently, these results are frequently applied to quantify the embrittling potency of individual solutes. Unfortunately, the values of the segregation energy of a solute at grain boundaries as well as at the surfaces obtained by various authors sometimes differ by more than one order of magnitude: such a difference is unacceptable as it cannot provide us with representative view on the problem of material temper embrittlement. In some cases it seems that these values do not properly reflect physical reality or are incorrectly interpreted. Due to the above mentioned large scatter of the segregation and embrittlement data a critical assessment of the literature results is highly needed which would enable the reader to avoid both the well known and less well known pitfalls in this field.

Dependence of the strengthening/embrittling energy, DE SE,I , and/or the strengthening/embrittling Gibbs energy, DG SE,I , on the difference of sublimation energies of a-iron and respective solute. Blue triangles represent experimental data of DG I 0,GB À DG I 0,FS at differently oriented grain boundaries. Symbols connected by vertical lines show limiting values of individual data. The red circles and green squares are the values calculated by DFT methods and by other theoretical approaches, respectively; the symbols of the same type correspond to the same source.

¹Institute of Physics, Czech Academy of Sciences, Na Slovance 1992/2, 1822 Prague, Czech Republic.
²Masaryk University