Abstract
Iron-chromium alloys are the basis for ferritic and ferritic-martensitic steels that will be used in future fission (generation IV) and fusion nuclear reactors. With Cr content between typically 8 to 12% [1], or even 14% in the matrix of some oxide dispersion-strengthened steels [2], one can expect the precipitation of a Cr-rich α’ phase that can be strongly accelerated under irradiation, due to point defect supersaturation. This precipitation can cause hardening and embrittlement. Radiation-induced segregation (RIS) is another important technological problem. It can lead to a Cr depletion at grain boundaries and therefore to a loss of corrosion resistance and again, to embrittlement. RIS in austenitic steels is well known and presents almost systematic trends: depletions of Cr and enrichments of Ni at grain boundaries. In ferritic steels, the experimental situation is far from being so clear: depletions and enrichments of Cr have been observed, without clear correlation with the irradiation conditions and the materials properties [3].
Highlights
Radiation-induced segregation (RIS) results from the elimination of excess vacancies (V) and self-interstitials (I) on sinks such as dislocations, grain boundaries, or free surfaces
RIS can be analyzed properly in the framework of the thermodynamics of irreversible processes, that gives the flux of a specie α as a function of the gradients of chemical potentials μβ : Jα =-∑Lαβ∇μβ
Atomistic Kinetic Monte Carlo (AKMC) simulations with thermodynamic and point defect parameters fitted on DFT calculations Good description of driving forces, diffusion properties and nucleation In Fe-Cr alloys
Summary
Atomistic Modelling of Segregation and Precipitation in Fe-Cr Alloys under Irradiation. With Cr content between typically 8 to 12% [1], or even 14% in the matrix of some oxide dispersion-strengthened steels [2], one can expect the precipitation of a Cr-rich α’ phase that can be strongly accelerated under irradiation, due to point defect supersaturation. The simulations are able to well reproduce the thermodynamic [4] and diffusion [5] properties of dilute and concentrated alloys, including the effects of the magnetic configurations and magnetic transitions, which are especially important in Fe-Cr alloys They give kinetics pf precipitation during isothermal annealing in good agreement with experimental studies [5]. The AKMC enables to study the interaction between segregation and precipitation [9]: typical cases will be presented
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