Optimization of Heat Treatment Profiles Applied to Nanometric-Scale ${\rm Nb}_{3}{\rm Sn}$ Wires With Cu-Sn Artificial Pinning Centers

Abstract

Nb3Sn is one of the most used superconducting materials for applications in high magnetic fields. The improvement of the critical current densities (Jc) is important, and must be analyzed together with the optimization of the flux pinning acting in the material. For Nb3Sn, it is known that the grain boundaries are the most effective pinning centers. However, the introduction of artificial pinning centers (APCs) with different superconducting properties has been proved to be beneficial for Jc. As these APCs are normally in the nanometric-scale, the conventional heat treatment profiles used for Nb3Sn wires cannot be directly applied, leading to excessive grain growth and/or increase of the APCs cross sections. In this work, the heat treatment profiles for Nb3Sn superconductor wires with Cu(Sn) artificial pinning centers in nanometric-scale were analyzed in an attempt to improve Jc . It is described a methodology to optimize the heat treatment profiles in respect to diffusion, reaction and formation of the superconducting phases. Microstructural, transport and magnetic characterization were performed in an attempt to find the pinning mechanisms acting in the samples. It was concluded that the maximum current densities were found when normal phases (due to the introduction of the APCs) are acting as main pinning centers in the global behavior of the Nb3Sn superconducting wire.