Anisotropic hardness and fracture toughness of highly aligned YBa sub(2)Cu sub(3)O sub(7- delta )

The hardness and fracture toughness of aligned YBa sub(2)Cu sub(3)O sub(7- delta ) obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., K sub(c)@) super(0)01 < ) K sub(c)@) super(1)00o)r K sub(c)@) super(0)10 )The extremely low values of the fracture toughness suggest that considerable toughening would have to be achieved in melt-textured 123 for any practical bulk application. The presence of 211 phase and silver particles may serve to enhance the fracture toughness of aligned 123 by crack deflection and crack tip blunting respectively.