Microstructural evolution of Bi-2223/Ag tapes during the cooling process after the first heat treatment

摘要

The microstructural evolution of Bi-2223/Ag tapes during cooling after the first heat treatment is investigated by SEM, XRD and EDS. Cooling was carried out after samples were heat treated at 840 deg C for 10 h. Samples were quenched in air from different temperatures during the cooling process. Investigation showed that the volume fraction of Bi-2223 increased during the initial stages of cooling, reaching a maximum of 93 percent at 780 deg C, and then began to decrease as the temperature fell below 780 deg C. CuO particles precipitated out from the liquid phase and grew into big particles at temperatures below 750 deg C. The Ca_2PbO_4 phase formed rapidly at the beginning of the cooling process, while the 3321 phase began to form only below 750 deg C. The formation and amount of the lead-rich phases are associated with the amount of the liquid present at high temperatures.