Impact of micro-alloying in ion-irradiated nickel: From the inhibition of point-defect cluster diffusion by thermal segregation to the change of dislocation loop nature

Micro-alloying strongly affects the incubation period of void swelling in irradiated face-centered cubic materials. However, the underlying mechanism, which relates to the formation of dislocation loops, is still unclear. Here, we investigate pure Ni, Ni-0.4wt.%Cr and Ni-0.4/0.8/1.2wt.%Ti as model materials, to gain insight into the solute effects on the loops evolution in the early stage of irradiation. The dislocation loop characteristics (mobility, Burgers vector, nature) are studied using in-situ transmission electron microscopy and ex-situ irra-diation with Ni+ ions at 450 degrees C and 510 degrees C for doses from 0.06 to 0.7 dpa. It appears that a tiny amount of Ti effectively increases the loop density, reduces the loop mobility and the stacking fault energy. It leads to an equal distribution among a/2 < 110 > perfect loop families. It also stabilizes self-interstitial loops against vacancy loops depending on Ti content and temperature. Our modeling of radiation-induced segregation, based on experiments and recent ab initio calculations of flux couplings, predicts a Cr enrichment and a Ti depletion nearby dislocation loops. It is in good agreement with our observations by X-ray spectroscopy in TEM and by atom probe tomog-raphy. However, the lowered loop mobility must be the signature of a thermal segregation rather than the impact of radiation-induced depletion. Indeed, oversized Ti atoms subsequently trapped at strained lattice sites around the dislocation line of the loop due to thermal segregation would inhibit its diffusion. This opens new per-spectives for future experimental investigations and radiation-effect modeling.

Automated summary

Micro-alloying significantly affects the incubation period of void swelling in face-centered cubic materials. The mechanism relating to the formation of dislocation loops is still unclear. This study uses pure Ni, Ni-0.4wt.%Cr, and Ni-0.4/0.8/1.2wt.%Ti as model materials to investigate the solute effects on loop evolution during early-stage irradiation. Experimental techniques including in-situ transmission electron microscopy and ex-situ irradiation are employed to study the characteristics of dislocation loops. The results show that a small amount of Ti increases loop density, while reducing loop mobility and stacking fault energy. It also stabilizes self-interstitial loops depending on Ti content and temperature.