Toughness and thermal shock resistance of YBa2Cu3O7-x composite superconductors containing Y2BaCuO5 or Ag particles

Macroscopic toughness measurements and the Vickers indentation technique ha ve been used to characterise sintered or melt-textured superconducting YBa2 Cu3O7, ceramics. A newly developed thermal shock resistance parameter, base d on the Vickers indentation technique, has been used. The crack propagatio n mechanisms observed in sintered ceramics have been analysed with respect to residual stress fields due to the anisotropy in thermal expansion coeffi cients, or to the difference with that of the Y2BaCuO5 ('211') inclusions. The addition of the '211' brittle phase does not increase the toughness and thermal shock resistance of sintered ceramics, but toughens the textured m aterials. An enhancement of the thermal shock resistance, through an increa sed R-curve behaviour, has been achieved by introducing a metallic silver d uctile phase into the microstructure, both in sintered and textured ceramic s. The evaluation of the latter needed the extension of the thermal shock r esistance parameter to the case of Palmqvist indentation cracks. Parallelly , a modelling of the thermal shock behaviour of textured ceramics is propos ed through the description of the microstructure as a stacking of YBa2Cu3O7 -x layers cracked along the (001) planes, joined by Y2BaCuO5 particles, cor responding to a low-stiffness material. (C) 2001 Published by Elsevier Scie nce B.V. All rights reserved.