Liquid Phase Diffusion Bonding of High Temperature Superconducting Ceramics

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In order to develop joining methods maintaining mechanical strength and superconducting property, YBCO(Y123) bulk superconductors were joined using YbBCO(Yb123), which had lower peritectic temperature than YBCO, added Ag2O as interlayer. The concept of the joining method in this study is based on the fact that the peritectic formation temperature(TP) of Yb123 is about 50K lower than that of Y123. The Samples were heated at about 1293K(above TP of Y123) for 10 minutes and slowly cooled down to 1198K.The microstructures of the joints revealed that Y element diffused from the bulk to the joining layers and Yb diffused from the joining layers to the bulk, and the joining part seemed to become more dense. As results of joining tests under such conditions that Ag2O content added to YbBCO was 0〜44 mass % and that joining temperature was 1213K 〜1293K, the joint strength increased in accordance with the joining temperature increase. Critical current density showed maximum value in case using the YbBCO interlayer added 10〜30 mass %Ag2O.Because of the boids occurred at the joint area, strength of the joint was inferior to that of the matrix, however, it was suggested that joint properties could be improved by selecting the joining time and pressure conditions. The possibility to improve the joining property of Y123 bulk was shown by use of Yb123 interlayer.