Weight-averaged solute segregations at grain boundaries in advanced ferritic alloys

Solute segregation can have profound effects on the atomic structures and properties of grain boundaries (GBs), and hence the overall mechanical properties of polycrystalline alloys. In this work, a two-step site-and GB-weighted average method was proposed to predict the temperature-dependent segregation behaviors and effects from first-principles. Validated by the experimental S enrichments at GBs, this method was extended to a series of alloying elements in ferrite alloys. The calculation results suggested that the equilibrium weight-averaged GB concentrations follow the general ordering of Y>La>Zr>Hf>Al>Si>Cr>Ti>W, and decrease slowly with temperature. The segregation of Y, La, Ce, Zr, Hf, Al and Si, evidently reduces the GB adhesion strength with La being the most detrimental, while Ti, Cr and W have only minimal impacts on GB adhesion. These segregation effects do not change much with temperature. The new method is not limited to ferritic alloys but can be extended to any other alloy systems.