Effect of Cr Concentration on ½ to Dislocation Loop Transformation in Fe-Cr alloys

Abstract

Radiation can produce both <100> and ½<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 ½<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 ½<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 ½<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 ½<111> loop as Cr concentration increases, indicating that the formation of <100> loops becomes energetically more and more unfavorable than ½<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 ½<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.