Critical current densities at 77 K and 4.2 K of Bi(2223) tapes prepared by cold and hot deformation

Monofilamentary Bi(2223) tapes have been prepared by the Powder-In-Tube technique using various alternatives for the final thermomechanical processing. In particular, both cold and hot deformation processes were investigated and their critical current densities at 77 K and 4.2 K were measured. For long cold rolled Bi(2223) tapes, transport j/sub c/ values up to 30000 A/cm/sup 2/ were obtained at 77 K and 0T. The value of j/sub c/ was found to increase from 17000 A/cm/sup 2/ at the oxide center to 46000 A/cm/sup 2/ at the borders of the oxide layer. At 4.2 K and 28 T, j/sub c/ values of 45000 and 30000 A/cm/sup 2/ were measured for B parallel and perpendicular to the tape surface, respectively. The j/sub c/ (B) hysteresis was found to disappear at higher fields. The present state of hot deformed Bi(2223) tapes is presented. For rolling temperatures up to 850/spl deg/C, a maximum of j/sub c/ (77 K, 0T)=18000 A/cm/sup 2/ was observed at 800/spl deg/C, j/sub c/ being considerably lower for higher rolling temperatures. The results obtained so far show generally lower j/sub c/ values than for cold rolled tapes. This is essentially due to microcracks and to sausaging effects, which are more pronounced than for cold rolled tapes. For static hot deformation at 800/spl deg/C of short, pressed Bi(2223) tapes an enhancement of j/sub c/ (77 K, 0T) by 20% up to >40000 A/cm/sup 2/ was observed. In addition, the decrease of j/sub c/ for B perpendicular to the tape surface is less pronounced compared to cold deformed tapes.<
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