Hot rolling of powder-in-tube Li-doped Bi(2212) tapes

Powder-in-tube Li-doped Bi(2212) tapes with high critical currents have been obtained by a hot rolling process. Hot rolling was accomplished in the final rolling stage after partial melting by preheating the rolls with infrared heaters to various temperatures ranging from 300°C to 410°C and then rolling the tapes directly from a 750°C furnace. T_c decreased after hot rolling and final heat treatment. Microstructural analysis shows improved grain alignment with increased hot rolling temperature. Due to the small thermal capacities of these Ag-clad BSCCO tapes, as well as the difference in temperature between the rolls and the furnace, the remnant liquid phase that termed from partial melting was melted during the 750°C preheat and subsequently formed a glassy phase upon contact with the heated rolls. The amount of glassy phase was reduced with increasing roll temperature. Results show that the enhancement of J_c was due to an improvement of grain alignment and reduction in the amount of secondary phases