The role of nickel in radiation damage of ferritic alloys

Abstract

According to the modern theory damage evolution under neutron irradiation depends on the fraction of self-interstitial atoms (SIAs) produced in the form of one-dimensionally glissile clusters. These clusters, having a low interaction cross-section with other defects, are absorbed mainly by grain boundaries and dislocations creating the so-called production bias. It is known empirically that addition of certain alloying elements influence many radiation effects, including swelling, however the mechanisms are unknown in many cases. In this paper we report the results of an extensive multi-technique atomistic level modeling study of SIA clusters mobility in bcc Fe-Ni alloys. We have found that Ni interacts strongly with the periphery of clusters affecting their mobility. The total effect is defined by the number of Ni atoms interacting with the cluster at the same time and can be significant even in low-Ni alloys. Thus 1nm (37SIAs) cluster is practically immobile at T<500K in the Fe-0.8at.% Ni alloy. Increasing cluster size and Ni content enhance cluster immobilization. This effect should have quite broad consequences in void swelling, matrix damage accumulation and radiation induced hardening and the results obtained help to better understand and predict the effects of radiation in Fe-Ni ferritic alloys.

Nanostructure evolution under irradiation in FeMnNi alloys: A “grey alloy” object kinetic Monte Carlo model

“…Molecular dynamics simulations showed that h1 1 1i SIA loops are effective to slow down and immobilize, especially, loops that approach TEM visible sizes. In particular, it was seen that, starting from 37 SIA in a cluster, for temperatures up to 600 K, the diffusion coefficient experiences a dramatic decrease, down to two orders of magnitude smaller than for the same loop in Fe [26]. This decrease in SIA clusters mobility, however, disappears fast with increasing temperature.…”

“…The effect of Ni on SIA loops seems in fact to be more subtle than that of Mn. Atomistic studies for a single SIA suggest that Ni solutes in the dilute limit do not influence the 3D migration of the h1 1 0i split dumbbell; however, the interaction of solute Ni with SIA clusters formed by h1 1 1i crowdions can be strong [26]. Molecular dynamics simulations showed that h1 1 1i SIA loops are effective to slow down and immobilize, especially, loops that approach TEM visible sizes.…”

“…However, while the slowing down of SIA clusters, affected by Mn concentration, can be justified both in terms of interaction between Mn atoms and self-interstitials, either in dumbbell or crowdion configuration, as suggested by DFT calculations [23,44,45], or of Ni atoms with larger SIA clusters, as suggested by recent molecular dynamics simulations [26], at the moment no clear mechanism has been identified to explain the slowing down or even the mobility suppression of vacancy clusters.…”

“…Recent molecular dynamics studies [26] show that Ni has also the effect of reducing the mobility of SIA loops, especially for relatively large ones. This effect is, however, not explicitly accounted for in the model, given that the slowing down predicted by Eqs.…”

Stability and mobility of small vacancy–solute complexes in Fe–MnNi and dilute Fe–X alloys: A kinetic Monte Carlo study

“…As a matter of fact, solute atoms can be transported by defects towards these nucleation sites, causing the clusters to grow in size. The effective ''pinning effect'' of solute atoms on SIA loops emerges from several studies [6][7][8], whereas the systematic arising of a vacancy drag effect in iron dilute alloys has been recently shown [9] to be a very effective means of solute transport towards defect sinks in RPV steels, and could hence confirm this mechanism. In particular, Mn is expected to have a specifically strong effect on SIA-loop mobility because of the strong interaction between Mn and crowdion, in analogy with the effect of Cr [7] and because it is known to efficiently diffuse via a dumbbell mechanism.…”