ALIGNMENT OF GRAINS IN BI1.6PB0.4SR2CA2CU3OX BY HOT DEFORMATION

The alignment of grains in sintered pellets of Bi1.6Pb0.4Sr2Ca2Cu3Ox with platelet microstructure, has been achieved by compressive deformation in air in the temperature range 830-860-degrees-C. The reduction in thickness of the pellet was achieved by rotating the platelets in such a way that their flat surfaces were aligned perpendicular to the direction of the stress, and by sliding the platelets over one another. During compression at 840-degrees-C, most of the alignment took place under stresses in the range 12-18 MPa, but after an engineering strain of 35.7% the stress increased rapidly, resulting in cracks on the round surface of the pellet. Due to rapid cooling after deformation at elevated temperatures, glassy and non-superconducting phases were formed from the partial melt, as indicated by the change in intensities of the x-ray diffraction pattern. As a result, T(c) of the deformed pellet was sometimes lower than that of the undeformed pellet by a few kelvin and transport J(c) at 77 K did not increase appreciably, even though there was considerable alignment of grains. However, upon annealing the deformed pellet at 840-degrees-C for 24 h in air, T(c) at zero resistance reached about 105 K and transport J(c) at 77 K was about 165 A CM-2, which was about 4 times that of the undeformed pellet. The density of the pellets, deformed at 860-degrees-C to 33.5% engineering strain, reached about 96% of the theoretical density. The Vicker's microhardness also increased due to the hot deformation.