极低温环境下立方相和四方相Nb_(3)Sn超导晶体力学及力-电耦合行为分析  

Comparative studies on the electromechanical coupling responses of cubic and tetragonal Nb_(3)Sn at extremely low temperature

作　　者：王涛 何宇新 乔力 WANG Tao;HE Yuxin;QIAO Li(Institute of Applied Mechanics,College of Mechanical and Vehicle Engineering,Taiyuan University of Technology,030024 Taiyuan,China)

机构地区：[1]太原理工大学机械与运载工程学院应用力学研究所,太原030024

出　　处：《应用力学学报》2024年第4期764-777,共14页Chinese Journal of Applied Mechanics

基　　金：国家自然科学基金资助项目(No.11772212)。

摘　　要：Nb_(3)Sn超导相转变中的力电耦合效应给超导磁体装备的电磁性能指标和安全运行带来不利影响。鉴于Nb_(3)Sn具有立方相和四方相两种相结构,建立了Nb_(3)Sn立方相、四方相和混合相晶体力学模型,以及考虑变形-临界温度退化和变形-正常态电阻率变化的力电耦合响应模型。研究结果表明,相结构会导致单晶体弹性力学性能有所区别,但静水压作用下不同相结构的Nb_(3)Sn多晶体,其局部应力状态与相结构无关,仅取决于晶粒形貌和取向。由于不同的相结构在外载下的费米面上电子态密度的演变规律基本一致,使得变形诱导的临界温度退化行为对相结构没有依赖性。对于混合相Nb_(3)Sn正常态电阻率变化而言,温度低于马氏体相变温度时,可以采用基于电子-电子散射假设得到的T_(2)规律来描述;当温度高于马氏体相变温度时,由于四方相向立方相的转变,需要考虑电-声子耦合作用对正常态电阻率的贡献,可以采用拓展的Woodard-Cody电阻率模型来描述宏观电阻率的应变效应。研究结果提高了对不同相的临界性能退化机理的认识。The superconductor Nb_(3)Sn has demonstrated great potential for its applications in the manufacturing of high field superconducting magnets and superconducting resonant cavities.The electromechanical coupling effect involved in the superconducting transition of Nb_(3)Sn has adverse effects on the electromagnetic performance and safe operation of superconducting magnets.In view of the fact that Nb_(3)Sn has two phase structures:cubic phase and tetragonal phase,based on the results of the first principles and the polycrystalline finite element calculation,the mechanical models of cubic Nb_(3)Sn,tetragonal Nb_(3)Sn 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 polycrystalline Nb_(3)Sn 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 orientation.The evolution of the electronic density of states at the Fermi surface under external loading is basically 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 Nb_(3)Sn can be characterized by the T_(2) 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-Co

关 键 词：Nb 3Sn 四方相 立方相 力-电耦合效应 

分 类 号：TB331[一般工业技术—材料科学与工程]