Direct formation of novel Frank loop and stacking-fault tetrahedron complex

Stacking-fault tetrahedron (SFT) is one kind of typical three-dimensional vacancy defect in quenched, deformed or irradiated face-centered cubic (FCC) metals, which can seriously degrade the mechanical properties of materials. It's generally believed that high stacking fault energy (SFE) is unfavorable for the formation of SFTs. Here, we report the first in-situ investigation of irradiation-induced formation of novel Frank loop-SFT complexes in Pd with extremely high SFE. Our findings reveal a new mechanism that vacancy clusters rearrange directionally to form SFTs due to the ambient stress deviations and compressive stress fields induced by interstitial Frank loops. Continuous hydrogen implantation will lead to a synergistic growth of the complex, while direct interaction between the Frank loop and SFT under thermal effect can cause the complex to disappear. These results uncover a unique formation mechanism for SFT and provide a new perspective for understanding nano-defects in high SFE metals.