Evolution of displacement cascades in Fe-Cr structures with different 001 tilt grain boundaries

M Abu-Shams and W Haider and I Shabib, RADIATION EFFECTS AND DEFECTS IN SOLIDS, 172, 364-378 (2017).

DOI: 10.1080/10420150.2017.1278760

Reduced-activation ferritic/martensitic steels of Cr concentration between 2.25 and 12wt% are candidate structural materials for next- generation nuclear reactors. In this study, molecular dynamics (MD) simulation is used to generate the displacement cascades in Fe-Cr structures with different Cr concentrations by using different primary knock-on atom (PKA) energies between 2 and 10keV. A concentration- dependent model potential has been used to describe the interactions between Fe and Cr. Single crystals (SCs) of three different coordinate bases (e.g. 310, 510, and 530) and bi-crystal (BC) structures with three different 001 tilt grain boundaries (GBs) (e.g. Sigma 5, Sigma 13, and Sigma 17) have been simulated. The Wigner-Seitz cell criterion has been used to identify the produced Frenkel pairs. The results show a marked difference between collisions observed in SCs and those in BC structures. The numbers of vacancies and interstitials are found to be significantly higher in BC structures than those found in SCs. The number of point defects exhibits a power relationship with the PKA energies; however, the Cr concentration does not seem to have any influence on the number of survived point defects. In BC models, a large fraction of the total survived point defects (between 59% and 93%) tends accumulate at the GBs, which seem to trap the generated point defects. The BC structure with Sigma 17GB is found to trap more defects than Sigma 5 and Sigma 13GBs. The defect trapping is found to be dictated by the crystallographic parameters of the GBs. For all studied GBs, self- interstitial atoms (SIAs) are easily trapped within the GB region than vacancies. An analysis of defect composition reveals an enrichment of Cr in SIAs, and in BC cases, more than half of the Cr-SIAs are found to be located within the GB region.

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