Strength and fracture toughness of hot-pressed bulk Bi2Sr2Ca2Cu3Ox and Bi2Sr2Ca2Cu3Ox/Ag at 77 and 300 K

A study was made of the effect of temperature (300 and 77 K) and orientation on the mechanical properties of bulk BSCCO 2223 and BSCCO 2223/Ag composites processed by hot-pressing. The unreinforced material was strongly textured and almost fully dense and its flexure strength was outstanding. The flexure strength of the composites showed the balance between the benefits due to the presence of Ag, and the harmful impact of higher porosity and reduced texture. The strength of all the materials was fairly independent of the orientation and temperature, although a noticeable improvement (6-20%) was found at 77 K when the crack propagation direction was parallel to the hot-press axis. The fracture toughness was mainly a function of the porosity with the dense, BSCCO 2223 material showing the highest value. In addition, the toughness was largely influenced by orientation and temperature, again reaching maximum (by up to 70%) in the specimens tested at 77 K with the crack plane parallel to the hot-press axis. This behavior was explained in terms of the crack deflection and of the toughening effect of ice. (C) 2002 Elsevier Science B.V. All rights reserved.