Improvement of Nb<inf>3</inf>Sn high field critical current by a two-stage reaction

Abstract

The grain structure of a commercial multifilamentary Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn wire has been investigated as a function of reaction temperature, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> , and time, t <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> . Results allow a quantitative description of grain growth. Based on the dependence of critical current, Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn area and grain size on the heat treatment conditions a two-stage reaction process is proposed to improve the critical current carrying capacity in magnetic fields greater than 10 Tesla. The first reaction converts the major part of the Nb to fine grained Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn at low T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</inf> . Subsequent high temperature ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_{R}\simeq</tex> 800°C) heat treatment for a short time ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t_{R}\leq1</tex> h) increases both T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> and B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</inf> due to composition approaching stoichiometry (or a higher degree of order) without detrimental grain growth. First experimental results show a remarkable improvement in the high field critical current for this two stage-reaction process.