Abstract---The evolution of the microstructure during heat treatment was investigated for dip-coated BizSr2CaCu20y(Bi-2212)/Ag and Ag alloy tapes as a function of temperature and oxygen partial pressure(Poz=0.01, 0.21 and 1 atm) using quenched and fully-processed tapes. The microstructures were essentially the same for Bi-2212 on pure Ag and on the Ag alloy. Although the melting temperature of Bi-2212 increased with increasing Po*, the solidification temperature(T,,I) of Bi-2212 for Poz=0.21 atm was higher than that for P o~= l atm. The volume fraction and grain alignment of Bi-2212 processed in Poz=O.Ol atm was smaller than in tapes processed in 0.21 and 1 atm, which were quite similar. HR-TEM studies on grain boundaries and AC susceptibility measurements suggest that the higher critical current density(J,) for tapes processed in PoZ=l atm than that for 0.21 atm is due to improved coupling of the grains.

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Specimens of Nb3Sn tape have been irradiated at ∼380 K with reactor-spectrum neutrons to fluences of 1.3×1019 n/cm2 (E>1 MeV) and the internal friction and dynamic Young’s modulus measured from 6 to 300 K. The softening of the lattice with decreasing temperature is seen to decrease from 40% of the room-temperature value at 10 K for unirradiated Nb3Sn to 94% at a fluence of 1.3×1019 n/cm2. The internal friction δ due to tetragonal domain-wall motion of the transformed material decreased with increasing fluence, being completely suppressed after ∼4×1018 n/cm2. The transformation temperature Tm decreased from ∼49 K for the virgin specimen to 22 K for a fluence of 3.8×1018 n/cm2 with no evidence of any tetragonal transformation at all for higher fluences. The lattice-dynamical and electronic changes responsible for these effects are not known at this time, but are seen to be correlated with the neutron-induced disorder.

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