Atomic-scale mechanisms of He/V ratio effect on helium bubble hardening in iron for neutron irradiated F/M steels

The helium-to-vacancy (He/V) ratio is a key factor related to the helium bubble hardening mechanisms induced by neutron irradiation in ferritic/martensitic (F/M) steels as advanced nuclear structural materials. According to the helium bubble hardening results in F/M steel irradiated in the spallation neutron source, the interactions between a 1/2<111>{110} edge dislocation and helium bubbles with various sizes of 0.7–3.0 nm in bcc-Fe under irradiation temperatures and room temperature was investigated by using molecular dynamics simulation. The effect of various He/V ratios in the ranges of zero to the highest He/V ratios, 1.85–4.0 of stable helium bubbles with no dislocation loop emission, on the interaction mechanisms was analyzed. The results indicated that the critical resolved shear stress (CRSS) drops rapidly to a very low stress level, and immediately bottoms out and rebounds to a very high stress level, when the He/V ratio increases from 1.0 to the highest He/V ratio. The significant change of CRSS values is not only related to the climbing degree of dislocation after releasing, but also related to the moment when the climb appears. A new repulsion mechanism of interaction between dislocation and bubble was proposed to elucidate the abnormal phenomena of the bottoming rebound of CRSS with a great climbing degree, according to the repelling interaction between helium bubble and superjog of dislocation with both strong compressive stress field.