Shock Compaction of YBa2 Cu3 O(sub 7-x) and HoBa2 Cu3 O(sub 7-x) Powders in a Metal Matrix.

摘要

Shock compaction of powders has several features with potential for processing high-J/sub c/ oxide superconductors. Because compaction occurs by applying 100 kbar pressures on fast mu sec timescales, compressive energy and heating are localized on powder particle boundaries. By using single-crystallite particles the method could be used to heat and bond grain boundaries while maintaining their interiors cool and stable. Shock processing of ceramic powders produces defects and fine grain size, which might increase flux pinning and J/sub c/. This paper summarizes results of compactions using single-phase orthorhombic powder specimens of YBa2 Cu3 O/sub 7-x/ or HoBa2 Cu3 O/sub 7-x/ mixed with 30 vol % Ag. Each powder specimen weighed less than 0.2 g. Dynamic pressures in the range 29-217 kbar were generated by impact of a 5 g plastic projectile at velocities in the range 0.77-3.26 km/s. Projectiles were accelerated with a two-stage light-gas gun. Representative pressure histories were calculated with a two-dimensional finite-element computer code. X-ray diffraction, optical microscopy, magnetic susceptibility, and electrical resistance measurements were made on the recovered compacts. X-ray and magnetic data show these oxide powders to be robust to shock compaction, essentially maintaining their chemical and crystal structures, oxygen stoichiometry, and bulk superductivity to shock pressures well above 100 kbar. The dependence of magnetic susceptibility on shock pressure is interpreted by a decrease in grain size which is consistent with the optical microscopy. At 167 kbar some tetragonal phase is formed. 24 refs., 12 figs. (ERA citation 14:022562)