Role of the Complex Interface Between Bi2Sr2CaCu2Ox Filaments and the Ag Matrix in the Mechanical and Electrical Behaviors of Composite Round Wires

Abstract

For a superconducting Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (Bi2212) multifilamentary composite round wire (RW), typically the interface between Bi2212 filaments and the Ag matrix become extremely complex after heat treatment, and all the time the question of how the unique interface structure affect the macro properties such as mechanical, electrical, and thermal behaviors has not been satisfactorily answered, mainly because it is very hard to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> measure the microstructure evolution and further evaluate its effect on these macro properties. Therefore, for this purpose, in this article, we made the modeling and numerical study on the role of the Bi2212/Ag interface in the mechanical and electrical behaviors of composite RWs. By using the randomly generated polygons method, we first reconstructed the cross section of Bi2212 composite RWs, especially in this reconstruction the complex Bi2212/Ag interface can be effectively characterized. On both of two models with and without the complex interface, we obtained the thermally residual stresses and strains due to cooling down from heat treatment, and then the mechanical response from the applied tensile strain. The comparative study further revealed that, for a practical Bi2212 RW with the complex interface, the distributions of the stress and strain are more uniform, which make the wire tend to safely and equivalently increase its limiting load capacity according to the maximum principal stress theory. In order to deeply understand the degradation of the critical current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> under applied tensile strain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\varepsilon $</tex-math></inline-formula> of Bi2212 RWs, we presented a current sharing model in which the current shares both in Bi2212 filaments and surrounding Ag matrix, taking into account the obstacle of cracks in the filament. By comparing the calculated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${I_c} - \varepsilon $</tex-math></inline-formula> curve with experimental data, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_c</i> degradation with the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\varepsilon $</tex-math></inline-formula> was very well interpreted by the mechanical damage and fracture of the microstructure of Bi2212 RWs.