Microcracking and mechanical properties of YBa2Cu3Ox ceramics

Elasticity, hardness and fracture data have been measured on superconducting YBa, Cu3 O~ ceramics with a relative density ranging from 87 to 93% and a grain size from about 10 to 2411m. For the 93% dense material a value of 112 GPafor the Young’s modulus and a hardness value of about 4.5 GPa are obtained. The strength andfracture toughness are dependent on cooling rate. A strength of 86 and 117 MPa are obtained for ‘fast’ and ‘slow’ cooling rates respectively. The corresponding fracture toughness measurements yielded 1•2 and 1•4 MPa. m1. The fracture toughness can be sign~cantly lower, as observed on some specimens, probably by reaction with water at the grain boundaries. Extensive microcracking, in agreement with theoretical expectations, was observed by microscopy. Further evidence from mercury intrusion porosimetry and N, adsorption analysis is presented. Possible consequences are discussed