Residual stress in nb3sn superconductor strand introduced by structure and stoichiometric distribution after heat treatment

Nb₃Sn, a widely-adopted superconducting material, suffers from fragility and sensitivity to strain. An elongation of 0.7% may lead to the irreversible failure of Nb₃Sn strands. Therefore, the stress and strain analysis of superconductors has attracted much attention from researchers. Many studies have anticipated these drawbacks to be greatly influenced by thermal expansion mismatch between the Nb₃Sn superconducting phase and matrix. X-ray diffraction (XRD) stress analysis was executed on a heat treated bronze strand at room temperature and its average axial residual stress was measured to be -135.7 MPa with fluctuation of about 300 MPa. The considerable stress fluctuation phenomenon may originate from diffusion, which was supported by electron probe microanalysis (EPMA) results. This work highlights the importance of component distribution on the stress status of a superconducting strand, and can supplement the thermal mismatch model.