**4. Conclusion**

In this work, we conduct analyses about the influence of segregated impurities on the properties of nickel grain boundaries. The problematics and controversy of results posed here have a dual character: fundamental and industrial. The selected impurities are eight light elements and eleven transition metals elements of the periodic table. The adopted methodology for this study was based on density functional theory widely used in recent years to predict the mechanical response of materials and their tenability as a function of alloying additions.

After optimization study, we have shown that the norm-conserving approach together with local density approximation is best suited to solve convergence problems as well as to give accurate results in the case of metallic systems. Furthermore, different GB models have been used in order to fulfill the required calculated property.

Calculations permitted us to confirm that light elements (column 13–16, periods: 2 and 3) have strong tendency to segregate at Ni grain boundary due to their small size and high electronegativity. However, their influence on the cohesion of the grain tensile strength (TTS) differs from one element to another. We also confirmed that sulfur and oxygen are the most embrittling elements in Nickel GB in accordance with established literature results.

Our calculations show that the transition metal elements (column 22–25 periods: 4–6) have a general tendency to segregate to the grain boundaries in a moderate way. Unlike light elements, these elements tend to strengthen the Ni grain boundaries, with the exception of Mn which acts as embrittler, in which we studied further in order to explain this case. We have shown that the magnetism of Mn plays an important role in the GB decohesion. Among these transition elements, we have shown that W and Re are the most consolidating for Ni GB and therefore are candidates for counter embrittlement of sulfur.
