科研之友
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摘要
Four sets of mono-element internal-Sn (MEIT) wires which have different Sn-Cu ratio and 1 at% Zr addition in one wire were designed and fabricated for investigating A15 phase formation kinetics of Nb-3 Sn superconductors. All samples underwent a 210 degrees C/50 h + 340 degrees C/25 h thermal duration for Cu-Sn alloying prior to the A15 phase formation heat treatment (HT). Four reaction temperatures of 650 degrees C, 675 degrees C, 700 degrees C, and 725 degrees C were chosen to study the temperature and time influence. All the beattreated samples were examined by scanning electronic microscope for A15 layer thicknesses that were then plotted versus HT time at different temperatures and were nonlinearly fitted. Superconducting quantum interference device magnetization measurements were used to determine the inductive J(C) variations for the heat-treated wires. The obtained results demonstrate that the A 15 phase growth is promoted by four factors: reaction temperature elevation, reaction time extension, Sn-Cu ratio enlargement, and the alloyed Zr addition. The phase formation kinetics of MEIT Nb3Sn superconducting wires is in agreement with Y-n = K(T)t relation and the A15 growth exponent n is affected by HT temperature and Zr alloying.
