Ab initio investigation of phosphorus and hydrogen co-segregation and embrittlement in α-Fe twin boundaries

International audienceWe propose a new statistical physics model to study equilibrium solute segregation at grain boundaries and the resultingembrittlement effect. This low-temperature expansion model is general and efficient, and its parameters can be obtainedfrom atomistic calculations. It is possible to take into account multiple species, multiple segregation sites with differentsegregation free energies, account for configurational entropy, grain radius and site competition between solutes. As anexample, the model is then applied to the study of phosphorus and hydrogen co-segregation at Σ3 109.5° 01̄1 {111}twin boundaries in α-Fe, using energetic parameters from density-functional theory calculations. We show that P–Hinteractions may lead to increased P segregation at grain boundaries and cause additional embrittlement compared tothe case where P and H are considered separately