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The optimization of the heat treatment profile for Nba Sn superconductor wires is one of the most difficult steps to process this material. The present work had the objective to optimize the heat treatment profile to form the Nb[sub 3]Sn phase. It was developed an internal-tin Nb[sub 3]Sn strand with 1.0 mm in diameter, 12 065 Nb filaments with average diameter of 3.4 µm, 26 cores of Sn and internal stabilization of Cu surrounded by Ta diffusion barrier. Samples were removed for heat treatment optimization using different profiles to analyze the Sn diffusion and CuSn formation at temperatures up to 575 °C. A final treatment at 700 °C was used to form the Nb[sub 3]Sn phase. After the heat treatments, samples were removed for microstructural characterization. Measurements of T[sub c] and J[sub c] were performed to analyze the influence of the heat treatments on the superconducting phase and on the transport properties. It was concluded that the use of a two step heat treatment of 575 °C/100 h + 700 °C/100 h is as efficient as the use of a heat treatment with more low temperature steps. [ABSTRACT FROM AUTHOR]

Almost all large scale applications of superconductivity use metallic superconductors transporting high current in high magnetic fields. In this work, it was developed a (Nb,Ta)3Sn multifilamentary superconductor wire using the niobium tube and the internal tin methods. This conductor was projected to be used in a MagnetoHydroDynamic (MHD) energy generator system and it had 222 filaments of NbTa + Cu + Sn distributed in six regions, with Nb diffusion barriers around each one, and a central Cu rod. Several heat treatment profiles of diffusion and reaction of the Sn with the NbTa alloy were used. Microstructural and superconducting characterizations were made. The results showed that heat treatment that presented better critical current densities was 200 °C/50 h + 670 °C/100 h, leading to jc on the superconducting phase around 2800 A/mm2 at 9 T. [Copyright &y& Elsevier]