Free surface impact on radiation damage in pure nickel by in-situ self-ion irradiation: can it be avoided?

Inversion of dislocation loop nature driven by cluster migration in self-ion irradiated nickel

“…The observed defect free layer can not only be explained by an increase of defect recombination due to a higher damage rate at the damage peak (2.7 x10 -4 dpa/s). Indeed, past experiment realized with the same damage rate shows that vacancy loops grow at this level of flux [19]. Therefore, the observed defect free layer is related to the implantation peak.…”

“…Nevertheless, recently, vacancy-type loops were identified for the first time as dominant in the microstructure, within the damage zones of Ni irradiated by self-ions at 450°C [18]. The same vacancy nature was identified in as-irradiated TEM thin foils [19] and Focus Ion Beam (FIB) specimens up to 1.5 µm irradiation depth [18]. Interstitial Frank loops were only occasionally detected within vacancy-type Frank loops eradicating the outer vacancy loop [18].…”

“…Some I-clusters in the fcc structure were suggested to be highly mobile and to migrate in long-range 1D motion while V-clusters have low mobility [20,31,32]. In our previous work [19], the microstructure of irradiated thin foil Ni was dominated by vacancy loops. Rate theory combined with an original production bias model was suggested to explain the vacancy nature of loops.…”

“…Interstitial Frank loops were only occasionally detected within vacancy-type Frank loops eradicating the outer vacancy loop [18]. These observations contrasts with the well-established interstitial loop nature in literature and could be explained by the high mobility of interstitial clusters escaping from the damage production zone [9,[19][20][21]. To better elucidate the mechanisms, full characterization of dislocation loops (their nature and type) along the ion irradiation profile is therefore essential and has never been explored in ion-irradiated Ni.…”

“…Rate theory combined with an original production bias model was suggested to explain the vacancy nature of loops. In the model, I-clusters formed within cascades are assumed to be partially (about 10% for 260 nm thickness at 510°C [19]) absorbed by free surfaces due to their high mobility, which can theoretically lead to the growth of vacancy loops.…”