The superconductor Nb3Sn has demonstrated great potential for its applications in the manufac-turing of high field superconducting magnets and superconducting resonant cavities.The electromechanical coupling effect involved in the superconducting transition of Nb3Sn has adverse effects on the electromag-netic performance and safe operation of superconducting magnets.In view of the fact that Nb3Sn has two phase structures:cubic phase and tetragonal phase,based on the results of the first principles and the poly-crystalline finite element calculation,the mechanical models of cubic Nb3Sn,tetragonal Nb3Sn as well as the mixture of the cubic phase and the tetragonal phase are established.The electromechanical coupling model,accounting for the mechanical deformation induced critical temperature degradation and the strain-dependent normal-state resistivity variations,is also developed.The results indicate that the phase structure will lead to the difference in the elastic properties of single crystal;however,the local stress state of poly-crystalline Nb3Sn with different phase structures under hydrostatic pressure is independent of the phase structure,and the grain boundary stress concentration depends only on the grain morphology and orienta-tion.The evolution of the electronic density of states at the Fermi surface under external loading is basical-ly the same for the different phase structures,which makes the mechanical deformation-induced critical temperature degradation response independent of the phase structure.The normal state resistivity variation of the mixed phase Nb3Sn can be characterized by the T2 law based on the assumption of electron-electron scattering if the temperature is lower than the martensitic transition temperature.When the temperature is higher than the martensitic phase transition temperature,the contribution of electron-phonon coupling to the normal state resistivity should be considered because the cubic phase transforms into a tetragonal phase;thus the extended Woodard-Cody resistivity model can be used to describe the strain effect of mac-roscopic resistivity.The results of this paper enhance the understanding of the mechanism of the degrada-tion of the critical temperature and provide some basis for understanding the effect of phase structure on the critical properties and normal state resistivity of Nb3Sn.
NETL
NSTL
万方数据
