| Summary: | Phosphorus atoms in steels accumulate at grain boundaries via thermal and irradiation effects and induce grain boundary embrittlement, which is experimentally confirmed by an increase in the ductile-brittle transition temperature. Quantitative prediction of phosphorus segregation at grain boundaries under various temperature and irradiation conditions is essential for preventing embrittlement. To develop a model of grain boundary phosphorus segregation in <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>α</mo></semantics></math></inline-formula>-iron, we studied the migration of a phosphorus atom in two types of symmetrical tilt grain boundaries (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Σ</mo></semantics></math></inline-formula>3[1-10](111) and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Σ</mo></semantics></math></inline-formula>5[100](0-13) grain boundaries) using molecular dynamics simulations with an embedded atom method potential. The results revealed that, in the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Σ</mo></semantics></math></inline-formula>3 grain boundary, phosphorus atoms migrate three-dimensionally mainly in the form of interstitial atoms, whereas in the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mo>Σ</mo></semantics></math></inline-formula>5 grain boundary, these atoms migrate one-dimensionally mainly via vacancy-atom exchanges. Moreover, de-trapping of phosphorus atoms and vacancies was investigated.
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