Interaction of He and He–V clusters with self-interstitials and dislocations defects in bcc Fe

The understanding of helium effects in synergy with radiation damage is crucial for the development of structural steels for fusion applications. Recent investigations in ultra-pure iron, taken as a basic model, have shown a drastic impact of dual beam (helium and iron) exposure on the accumulation of radiation-induced dislocation loops in terms of strong bias towards a₀/2〈1 1 1〉 loops, while a₀〈1 0 0〉 loops are mostly observed upon iron ion beam. In this work we perform a series of atomistic studies to rationalize possible mechanisms through which He could affect the evolution of microstructure and bias the population of a₀/2〈1 1 1〉 loops. It is shown that He atoms are dragged by gliding a₀/2〈1 1 1〉 loops. This strongly suppresses loop diffusivity and in turn it prohibits the mutual interaction of a₀/2〈1 1 1〉 loops, being prerequisite of the formation of a₀〈1 0 0〉 loops, as well as it reduces the disappearance of a₀/2〈1 1 1〉 loops at sinks. A scenario for the microstructural evolution in the single- and dual-beam conditions is discussed