MICROSTRUCTURALLY OPTIMIZED HEAT-TREATMENT FOR MELT-PROCESSED, AG CLAD BI2SR2CACU2OY TAPE - STEP-SOLIDIFICATION MELT PROCESSING

We have studied the behavior of (Sr1-xCax)CuO2 (1:1) and the developme nt of Bi2Sr2CaCu2Oy (2212) alignment during melt processing of silver- clad 2212 tapes in air in the critical temperature region of 870-860 d egrees C. We found that remnant 1:1 grains can be reduced in size with extended annealing just below 865 degrees C. The highest 2212 alignme nt was achieved by annealing just below the 2212 solidus temperature ( 870 degrees C). An alignment mechanism based on grain growth of fortui tously 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. Base d on the microstructural data obtained from this study, a heat treatme nt that uses step-wise cooling (step solidification) was developed yie lding a microstructure consisting of highly aligned 2212 and small 1:1 grains.