Microstructure Evolution in Fe and Fe-Cr Alloys with OKMC Methods

Abstract

The type of damage observed under transmission electron microscopy (TEM) in b.c.c. Fe and FeCr alloys under irradiation is very dependent on the irradiation conditions. At high doses the damage consists mostly of ½ <111> and <100> loops, which are considered to be of interstitial type [1,2]. Depending on the type of irradiation and the irradiation conditions, the ratio of one type of loop with respect to the other changes, with situations in which only one of the two types of loops are observed. The formation of <100> loops is still a controversial issue, with different models arising in the last few years. Experimentally, even the nature of these loops (vacancy or interstitial type) is still under debate under certain situations. Moreover, the type of irradiation (ion implantation vs. neutron irradiation) also changes the type and distribution of these defects.In an attempt to shed some light into this complex system, we have developed models to study the damage of Fe and FeCr under irradiation. We combine results from density function theory (DFT), molecular dynamics (MD) and object kinetic Monte Carlo (OKMC) to study the production and evolution of the damage to time scales that can be directly compared to experiments. In this work we will discuss one particular issue: the differences between ion implantation and neutron irradiation. Currently, ion implantation is commonly used to obtain information about defect production and defect evolution, in an attempt to build models for neutron damage. We will point out the differences and commonalities between the two types of irradiation in the particular case of Fe, and those aspects that should be taken into consideration when building models for neutron irradiation from information obtained from ion implantation.We will describe results of damage evolution in Fe using two different models for <100> loop formation: one where <100> loops are formed from the interaction between ½ <111> loops (based on simulations by Marian [3] and Terentyev [4]) and a second one where two populations of loops are formed directly in the collision cascade and evolve independently. This last model is based on the observation of stable immobile clusters from DFT calculations [5]. The population of loops formed as a function of dose for different irradiation conditions is explored and results compared to experiments. The validity of the models and the influence of the different parameters are discussed. In particular, we will study how the mobility of <111> interstitial loops changes both the total concentration of visible defects as well as the ratio of <111> vs. <100> loops and compare the results with experimental data available, as shown in the Fig. 1. In this case the experiments are from reference [1]. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. nd Int. Workshop Irradiation of Nuclear Materials: ...

Kinetic Monte Carlo Simulations of Irradiation Effects

“…Within the object KMC designation, it is also possible to further sub-divide the techniques into those that explicitly treat atoms and atomic interactions, which is often denoted as atomic Kinetic Monte Carlo (AKMC), or Lattice KMC (LKMC), and which was reviewed by Becquart and Domain (Becquart and Domain 2010), versus those that track the defects on a lattice, but without complete resolution of the atomic arrangement. This later technique is predominately referred to as object Monte Carlo (OKMC), and used in such codes as BigMac (Johnson et al 1998) (Caturla et al 2016), LAKIMOCA (Domain et al 2004), MMonca (Martin-Bragado et al 2013) and others (Figure 1). In this chapter, we will designate by OKMC, the mesoscopic version of the object kinetic MC and by AKMC the atomistic version of the object kinetic MC.…”

“…Note that rigid lattices are not mandatory either for larger scale KMC approaches such as OKMC and EKMC, as demonstrated for instance in the codes BIGMAC (Caturla et al 2016) and JERK (Dalla Torre et al 2005).…”