Study on the mechanism of He effect on dislocation loop formation in three types of dual ion beam irradiations

A comprehensive investigation was conducted to explore the impact of helium on dislocation loops in RAFM steel. This was achieved by employing three types of dual-beam irradiations, which include simultaneous dual-beam irradiation with Ar++He+, sequential dual-beam irradiation with Ar+/He+ and He+/Ar+. In addition, single-beam irradiation with Ar+ and He+ were also performed for reference. The irradiation temperature is 723 ± 5 K. The evolutions of dislocation loop were characterized by transmission electron microscopy (TEM). After He+ irradiated to 0.005 dpa, high-density loops with an average size of 4.3 nm were observed. The main mechanism for the formation of the loops at such a low damage dose should be attributed to the process of the ejection of self-interstitial atoms triggered by He clusters. Significantly, in the RAFM steel exposed to Ar++He+ irradiation, the dislocation loops exhibit a significantly larger average size compared to those resulting from Ar+/He+ and He+/Ar+ irradiation. The loop density produced by He+/Ar+ is the largest, and the loop density produced by Ar+/He+ is the smallest. The order of the amount of self-interstitial atoms (loops) caused by three types of dual ion beam irradiation is Ar++He+ > He+/Ar+ > Ar+/He+.