Crack propagation effects on the critical temperature degradation of superconducting Nb3Sn single crystal

The irreversible degradation of Nb3Sn critical performance caused by the crack propagation brings challenges to the reliability of Nb3Sn service equipment. In this paper, the crack propagation behavior of Nb3Sn single crystal was studied by molecular dynamics method. The results show that amorphous transformation occur in Nb3Sn samples with cracks under the applied loading conditions. On the basis of these results, the electronic structures of different regions in the cracked sample are studied by first principles method. The critical temperature response in this process is analyzed in combination with our proposed trans-scale electromechanical coupling model. The physical mechanism behind the critical temperature degradation caused by the transition between the cracked surface and the amorphous zone at the crack tip is discussed. Amorphous states and the crack surface destroy the special kind of bonding in the atom chain direction, inducing the electronic band structure distortions. The density of states curve of Nb3Sn no longer exhibits the characteristic peaks near the Fermi surface observed in cubic crystalline Nb3Sn. The intrinsic relationship between the crack propagation, the electronic structure evolution driven by the local atomic rearrangements, and the irreversible critical temperature degradation of cracked Nb3Sn is revealed by the given model. The results deepen the understanding of the electromechanical coupling behavior of Nb3Sn under complex deformation.