Microstructurally optimized heat treatment for melt-processed, Ag clad Bi2Sr2CaCu2Oy tape step-solidification melt processing

Abstract We have studied the behavior of (Sr 1− x Ca x )CuO 2 (1:1) and the development of Bi 2 Sr 2 CaCu 2 O y (2212) alignment during melt processing of silver-clad 2212 tapes in air in the critical temperature region of 870-860°C. We found that remnant 1:1 grains can be reduced in size with extended annealing just below 865°C. The highest 2212 alignment was achieved by annealing just below the 2212 solidus temperature (870°C). An alignment mechanism based on grain growth of fortuitously aligned, plate-like 2212 grains within a mostly two-dimensional environment (opportunistic grain growth) was proposed to explain the high degree of alignment that can develop in melt-processed tape. Based on the microstructural data obtained from this study, a heat treatment that uses step-wise cooling (step solidification) was developed yielding a microstructure consisting of highly aligned 2212 and small 1:1 grains.