Effect of Segregation of Ni and Cr at Dislocation Loops on Their Interaction with Gliding Dislocations in Irradiated Fe−Ni−Cr BCC Alloys

Abstract

Ferritic–martensitic steels alloyed with chromium and containing nickel impurities are considered as promising structural materials for nuclear and thermonuclear power engineering. During operation, the plastic properties of such materials degrade under the influence of neutron irradiation caused by the generation of radiation defects of the crystal structure, in particular, dislocation loops and new phases (precipitates). In this paper, an atomistic computer simulation of the interaction of mobile edge dislocations with dislocation loops having the 〈100〉 and 1/2〈111〉 Burgers vectors forming a single extended defect with Ni−Cr precipitates is performed using the classical molecular dynamics method at various temperatures (300 and 600 K). Such composite radiation-induced defects cause a change in the plastic properties of the irradiated material due to radiation hardening. The results of studying the interactions of gliding dislocations with loops (both in pure iron and in the Fe−Ni−Cr alloy, taking into account the precipitation of Ni and Cr at dislocation loops) show that the presence of an increased concentration of chromium and nickel atoms near the dislocation-loop perimeter at 300 K either decreases the critical stress for passing the dislocation through a defect (by more than 50 MPa) for the 〈100〉 loops at 300 K or increases it for the 1/2〈111〉 loops at 300 K. At a high temperature (600 K), the presence of Ni and Cr impurities near the dislocation loop leads to an increase in the critical stress for both types of loops. It is shown that the presence of an increased concentration of Ni and Cr atoms near the loop perimeter facilitates or hinders (depending on the specific dislocation-loop configuration) the transverse gliding of dislocation segments, complicates the possibility of the resplitting of junction segments of the dislocation and loop in the plane of loop location, and causes the immobilization of the loop having the [111] Burgers vector parallel to the gliding plane of the dislocation at 300 K.