Effect of the partial melting process on the phase assemblage and microstructure of the (Bi,Pb)-2223/Ag strip

The effect of different stages of the partial melting process on the phase component and microstructure of (Bi,Pb)-2223/Ag strip was analyzed and compared to the normal two-stage heat treatment process. The results show that some of the (Bi,Pb)-2212 phase melted and decomposed into (Sr,Ca)₂CuO₃, (Sr,Ca)Cu₂O₃ and rich (Bi,Pb) liquid phase. At the same time, the (Sr,Ca)₂CuO₃ and (Sr,Ca)Cu₂O₃ phases grew rapidly. During cooling and phase formation, the (Sr,Ca)₂CuO₃ and (Sr,Ca)Cu₂O₃ phases stop growing when they reach a certain size and react with liquid phase to recreate the (Bi,Pb)-2212 phase with good orientation. At the phase formation stages, the (Bi,Pb)-2223 phase during transformation from the (Bi,Pb)-2212 phase inherits the good orientation of (Bi,Pb)-2212 phase. This results in an improvement in the texture and the density of the (Bi,Pb)-2223 phase which in turn results in an improvement of the critical current. The final strip made by the partial melting process has a critical current of 51 A (while the strip made by the normal two-stage heat treatment process have the lower critical current of 36 A). Thus the new method increases the critical current by about 40%.