Mechanisms of radiation strengthening in Fe-Cr alloys as revealed by atomistic studies

A review of experimental results shows that the dependence on Cr content of radiation-induced strengthening in Fe-Cr alloys and ferritic/martensitic steels is peculiar, exhibiting an increase as soon as Cr is added, followed by a local maximum and then a local minimum. This dependence is to date unexplained. In this paper we try to rationalise it, by reviewing recent (published and unpublished) molecular dynamics simulations work, devoted to the investigation of several possible mechanisms of radiation strengthening in Fe-Cr. In particular, the following questions are addressed quantitatively: (i) Does Cr influence the glide of dislocations? If so, how? (ii) Does Cr influence the interaction between dislocations and radiation-produced defects? If so, why? The latter question involves also a study of the interaction of moving dislocations with experimentally observed Cr-enriched loops. We find that the fact of shifting from a loop-absorption (pure Fe) to a loop-non-absorption (Fe-Cr) regime, because of the Cr-enrichment of loops, contributes to explaining why Fe-Cr alloys harden more under irradiation than Fe. If, in addition, the existence of a large density of invisible and Cr-enriched loops is postulated, the origin of the effect becomes even more clear. Moreover, the different strength of < 111 > and < 100 > loops as obstacles to dislocations movement, depending on whether or not loop absorption can occur, might explain why radiation strengthening decreases between 2% and 9%Cr. The formation of alpha' precipitates, on the other hand, explains why radiation strengthening increases again above 9%Cr. Altogether, these effects might explain the origin of the minimum of radiation-induced embrittlement at 9%Cr, as correlated to strengthening. (C) 2013 Elsevier B.V. All rights reserved.