High-Energy Ion Irradiation Induced Stepped Twins in the Ag Sheath of Bi2212 Superconductors

Silver (Ag) alloys have been widely used as the sheath material of Bi2212 superconductors; however, the irradiation resistance of Ag sheath is still not well understood. In this work, the transmission electron microscopy (TEM) observations indicate that the stepped twins could be generated in the Ag sheath after high-energy He + ion irradiation, in marked contrast to flat twins formed before irradiation. The average width of the twin boundaries, as well as the angle between two adjacent grains, was greatly increased after irradiation. This is probably attributed to the frequent interactions between the irradiation-induced defect clusters and twin boundaries. Two possible formation mechanisms of the stepped twins, including migration and detwinning of flat twins, are discussed accordingly. In addition, nanoindentation test results reveal an obvious hardening phenomenon of the irradiated Ag sheath, which was mainly associated with the formation of the stepped twins. This work provides a solid basis for further understanding on the interactions of twin boundary and irradiation defect in Ag sheath, which will be helpful for designing the twinned sheath materials with improved radiation tolerance and excellent mechanical properties through engineering formation of the twins.