[SY-B1] Multiscale modelling of radiation damage evolution in Fe and Fe-based alloys
In order to predict the behaviour of materials used in places where radiation is present, many aspects must be considered. The macroscopic effects like swelling and cracking, are a product of defect evolution starting at atomistic level. The energetic ion will, on the atomic level, transmit energy to lattice atoms, which will start collision cascades in the material. To be able to predict what the irradiation will do to the material, we must start on this level. The problem arises from that there is no single method that can accurately simulate everything from single atoms or electrons up to macroscopic parts that builds up the construction. To tackle this problem, a combination of two or more methods can be used consecutively, to be able to extend the time and/or length scale of the simulation. In this study, we focus on extending the time scale, to be able to predict the evolution of irradiation induced defects.
To study the irradiation effect in Fe and Fe-based alloys we utilize Molecular Dynamics (MD), to simulate the primary damage production on an atomistic level. The simulations are carried out by giving a recoil energy to a random atom in the simulation box. These simulations are very accurate to study the movement of all atoms, but are limited to nanoscale simulation boxes and times on the pico- or nanosecond time scale. The length scale is sufficient to accurately simulate the defect production, however the time scale is not sufficient for a long term evolution of the system. This long term evolution is needed to obtain comparable results with experiments and to compare with materials in use in these kinds of environments. To remedy the time scale problem, we utilize Kinetic Monte Carlo (KMC), to obtain longer time scales. A special version of KMC, Self-Evolving Atomistic KMC (SEAKMC), is used as no predefined and pre-calculated barriers are needed. This on-the-fly method is perfect for cases where the defects produced can have many different complicated structures. In these cases, it would be impossible to predict their structure beforehand and calculate all the barriers. A combination of MD and SEAKMC is used to both accurately predict the produced primary damage (with MD) as well as its evolution (with SEAKMC), before a second cascade will hit the same region, as in experimental cases where intensive irradiation is present.
To study the irradiation effect in Fe and Fe-based alloys we utilize Molecular Dynamics (MD), to simulate the primary damage production on an atomistic level. The simulations are carried out by giving a recoil energy to a random atom in the simulation box. These simulations are very accurate to study the movement of all atoms, but are limited to nanoscale simulation boxes and times on the pico- or nanosecond time scale. The length scale is sufficient to accurately simulate the defect production, however the time scale is not sufficient for a long term evolution of the system. This long term evolution is needed to obtain comparable results with experiments and to compare with materials in use in these kinds of environments. To remedy the time scale problem, we utilize Kinetic Monte Carlo (KMC), to obtain longer time scales. A special version of KMC, Self-Evolving Atomistic KMC (SEAKMC), is used as no predefined and pre-calculated barriers are needed. This on-the-fly method is perfect for cases where the defects produced can have many different complicated structures. In these cases, it would be impossible to predict their structure beforehand and calculate all the barriers. A combination of MD and SEAKMC is used to both accurately predict the produced primary damage (with MD) as well as its evolution (with SEAKMC), before a second cascade will hit the same region, as in experimental cases where intensive irradiation is present.