[SY-B4] Kinetics of Precipitation in Fe-Cr and Fe-Cr-C alloys under Irradiation
Invited
In ferritic steels, the precipitation of the Cr-rich α’ phase leads to a degradation of mechanical properties. Below 400°C, the precipitation is usually too slow to be a real concern, but it can be significantly accelerated by irradiation, due to an increase in point defect concentrations. Irradiation also produces a ballistic mixing between Fe and Cr atoms, and therefore prevent the nucleation of α’ precipitates or the dissolution of existing ones.
We present a multiscale approach which models these contradictory effects by taking into account the different mechanisms of atomic transport taking place under irradiation: the creation of vacancies and self-interstitials and the ballistic mixing within displacement cascades, the thermally activated diffusion of point defects, and their elimination at sinks or by mutual recombination. The method combines DFT calculations (which provide the fundamental information on thermodynamics and point defects properties), atomistic Kinetic Monte Carlo Simulations (to model the diffusion of point defects and the α’ precipitation), and Cluster Dynamics (to model the evolution of the sink density under irradiation). The simulations show that the acceleration of the α’ precipitation occurs under irradiation at low or moderate dose rates, but that ballistic dissolution becomes dominant under ion irradiation at high dose rates -- due to a large density of sinks that limits the point defect supersaturation.
The results of the simulations are compared with recent experimental studies. The same multiscale approach is used to model the diffusion of carbon atoms in Fe-Cr alloys and their strong interaction with point defects. We will consider their possible effect on Fe and Cr diffusion, and on the kinetics of α’ precipitation under irradiation.
We present a multiscale approach which models these contradictory effects by taking into account the different mechanisms of atomic transport taking place under irradiation: the creation of vacancies and self-interstitials and the ballistic mixing within displacement cascades, the thermally activated diffusion of point defects, and their elimination at sinks or by mutual recombination. The method combines DFT calculations (which provide the fundamental information on thermodynamics and point defects properties), atomistic Kinetic Monte Carlo Simulations (to model the diffusion of point defects and the α’ precipitation), and Cluster Dynamics (to model the evolution of the sink density under irradiation). The simulations show that the acceleration of the α’ precipitation occurs under irradiation at low or moderate dose rates, but that ballistic dissolution becomes dominant under ion irradiation at high dose rates -- due to a large density of sinks that limits the point defect supersaturation.
The results of the simulations are compared with recent experimental studies. The same multiscale approach is used to model the diffusion of carbon atoms in Fe-Cr alloys and their strong interaction with point defects. We will consider their possible effect on Fe and Cr diffusion, and on the kinetics of α’ precipitation under irradiation.