Effect of Cr Concentration on 1/2 <111> to <100> Dislocation Loop Transformation in Fe-Cr alloys

Radiation can produce both <100> and 1/2 <111> type dislocation loops in Fe-Cr based ferritic/martensitic alloys. However, contradictory experimental results have been reported on how Cr concentration affects the ratio of <100> to 1/2 <111> loops. In this study, firstly molecular dynamics simulations are conducted to study how Cr concentration affects the formation probability of <100> loops from overlapping cascades on a pre-existing 1/2 <111> loop in a series of Fe-Cr alloys with 0 - 15%Cr at 300 K using a concentration-dependent interatomic potential. Our atomistic modeling directly demonstrates that the ratio of < 100> to 1/2 <111> loops decreases with the increasing Cr concentration, which is consistent with many experimental observations. Next, independent molecular statics calculations show that the formation energy of a <100> loop has a much faster increase rate than that of a 1/2 <111> loop as Cr concentration increases, indicating that the formation of <100> loops becomes energetically more and more unfavorable than 1/2 <111> loops as the Cr content increases. Using a different interatomic potential, the Cr dependence on the <100> loop formation probability is weak, because this potential predicts that Cr addition does not change the relative energy difference between <100> and 1/2 <111> loops. Our results provide an alternative explanation for why Cr can suppress the formation of <100> loops in Fe-Cr alloys, which can be applied to all <100> loop formation mechanisms. The possible effects of other alloying elements on the formation of <100> loops in Fe-based alloys are also discussed. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The study investigates the effect of Cr concentration on the formation of dislocation loops in Fe-Cr alloys through molecular dynamics simulations and molecular statics calculations. It is found that the ratio of <100> to 1/2 <111> loops decreases with increasing Cr concentration, and the energy barrier for <100> loop formation increases faster than that for 1/2 <111> loop formation as Cr content increases. Different interatomic potentials result in varying Cr dependencies on the formation probability of <100> loops.