A detailed theoretical study was made of the segregation and strengthening/embrittling energy of sp-elements from the 3rd, 4th and 5th period (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb, Te) at the Σ5(210) grain boundary in face-centered cubic ferromagnetic nickel. For comparison, an investigation was also made of the segregation of these impurities at the (210) free surface. On the basis of ab initio electronic structure calculations, full relaxation of the geometric configuration of the grain boundary and free surface without and with impurities was performed and the effect of impurities on the distribution of magnetic moments was analysed. Whereas there was a slight enhancement of magnetization at the clean grain boundary and free surface with respect to bulk nickel (3–7 and 24%, respectively), the studied impurities entirely kill or strongly reduce ferromagnetism at the grain boundary and in its immediate neighbourhood so that magnetically dead layers were formed. This effect, which was due to the hybridization of the impurity sp-states and nickel d-states, was even more pronounced at the impurity-decorated (210) free surface. The preferred segregation sites at the Σ5(210) grain boundary for the sp-impurities studied, their segregation enthalpies and strengthening/embrittling energies with their decomposition into the chemical and mechanical components, were determined. It was found that interstitially segregated Si was a grain-boundary cohesion enhancer, substitutionally segregated Al and interstitially segregated P with none or minimum strengthening effect and interstitially segregated S, Ge, As and Se and substitutionally segregated Ga, In, Sn, Sb and Te were grain-boundary embrittlers in nickel.

The Effect of Segregated sp-Impurities on Grain-Boundary and Surface Structure, Magnetism and Embrittlement in Nickel. M.Všianská, M.Šob: Progress in Materials Science, 2011, 56[6], 817-40