Effect of the Heat Treatment Applied During the Welding Process on Superconducting Properties of the Welded YBCO Samples

Abstract

Two Y123 samples labeled as Y1 and Y2 were welded by using a Y123 solder reagent labeled as YA. Y1 and Y2 samples were produced by top seed melt growth (TSMG) method in Y123 + 30 wt.% Y211 composition and YA was produced by melt powder melt growth (MPMG) method in Y123 + 30 wt.% Y211 + 20 wt.% Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O composition. Artificial grain boundaries were created with the solder reagent and a pressure source was used during the welding process to obtain larger bulk superconducting samples. Welded sample was cut horizontally into three slices and these slices were named top down WY1, WY2 and WYA. Some superconducting properties such as superconducting transition temperature ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) and critical current density ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) of the welded samples were investigated before and after the welding process. Good quality welds obtained mechanically and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values determined from the resistivity measurements are around 92 K for all specimens, stating that the welding has no negative effect on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . The calculated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values are 13.71, 12.08 and 9.97 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the Y1, Y2 and YA specimens cut from the samples before welding process while the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values are 2.33, 21.13 and 14.42 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for WY1, WY2 and WYA specimens cut from the welded sample after welding process, respectively. It was observed that the welding process enhanced the superconducting properties of the welding region. After the welding process, the superconducting properties of the high-quality samples oriented in the c-axis decreased less than the samples that do not have a preferential orientation or grain structure.