Modeling of Phosphorus Transport by Interstitial Dumbbell in α−Iron Using First-Principles-Based Kinetic Monte Carlo

Abstract

We have evaluated the diffusion coef cient of phosphorus in α-iron transported in the form of a mixed dumbbell using a kinetic Monte Carlo simulation based on rst-principles calculations. The evaluated diffusion coef cient has been compared with both that for the migration mode via octahedral interstitial sites and that for the migration mode of the vacancy mechanism estimated previously using a rst-principles-based kinetic Monte Carlo simulation. As a result, we have con rmed that the phosphorus diffusion by the two interstitial migration modes is much faster than that of the vacancy migration mode. In addition, by applying the rate-theory model incorporating the evaluated coef cients to the simulation of irradiation-induced grain-boundary phosphorus segregation, it was made clear that modi cations are required to the previous model for GB P segregation and for evaluating GB P coverage.

Effect of Grain Boundary on Diffusion of P in Alpha-Fe: A Molecular Dynamics Study

“…The tempered embrittlement and radiation embrittlement has been observed in steel during rapid cooling from higher temperature and irradiation [10]. Phosphorus is one of the major impurity amongst the embrittlement species in steel [10][11][12]. The Phosphorus grain boundary segregation plays an important role in the intergranular embrittlement of the reactor pressure vessel (RPV), especially under irradiation enhancing diffusion [11,13].…”

“…Phosphorus is one of the major impurity amongst the embrittlement species in steel [10][11][12]. The Phosphorus grain boundary segregation plays an important role in the intergranular embrittlement of the reactor pressure vessel (RPV), especially under irradiation enhancing diffusion [11,13]. The embrittlement is instigated due to the shift of Ductile-to-Brittle Transition Temperature (DBTT) to higher temperatures, resulting in the decrease of the GB cohesion.…”

Atomistic simulation of phosphorus segregation to Σ3 (111) symmetrical tilt grain boundary in α-iron

“…Regarding irradiation-induced GB P segregation, some modeling studies using the rate theory is reported [19,20], but none of them considers such a strain field near GBs: in those models, P diffusion based on the first-principles calculations for the bulk region, are applied to the entire region. Besides, the models do not consider the trapping process at GBs, so that they cannot examine the influence of properties of different GBs, such as segregation energy and the amount of segregation sites, on the P segregation.…”

On the Modelling of Thermal Aging through Neutron Irradiation and Annealing

“…In recent years, much attention has been paid to modelling of self-diffusion and P diffusion in Fe and dilute Fe-P alloys. Molecular dynamics, ab initio, and kinetic Monte Carlo calculations are applied to elucidate the mechanisms and diffusion parameters [37][38][39][40][41]. Ab initio calculations reveal relatively high binding energies between P atoms and vacancies (vacancy drag effect) and very high binding energies of mixed Fe-P dumbbells on the order of 1 eV and their high mobility.…”

“…e authors suppose that a significant portion of P atoms is trapped in stable two-P complexes or segregated on point defect clusters. Both vacancy and interstitial (via mixed Fe-P dumbbells and via octahedral positions) diffusion of P atoms were used [39,41] to fit some experimental data on GB phosphorus accumulation in RPVs at neutron fluences up to 10 24 n/m 2 . For fitting the data, an unreally high PD sink strength of 2 × 10 18 m −2 was adopted in calculations.…”