EFFECTS OF SILVER ADDITIONS ON RESISTANCE TO THERMAL-SHOCK AND DELAYED FAILURE OF YBA2CU3O7-DELTA SUPERCONDUCTORS

The effect of silver (Ag) addition on the resistance to thermal shock and delayed failure of YBa2Cu3O7-delta superconducting wires has been evaluated. Resistance to thermal shock was evaluated by measuring the critical-current density (J(c)) as a function of the number of thermal cycles for YBCO and its composites with 15 vol. % Ag additions. Composite YBCO-Ag wires show a slower decrease in J(c) than does monolithic YBCO as the number of thermal cycles increases. The nature of delayed failure was studied by measuring strength (sigma(f)) as a function of loading rate (sigma) and evaluating the value of the subcritical crack growth parameter N[sigma(f) = Asigma1/(N+1)]. The value of the N parameter was observed to increase slightly from 35 for YBCO to 41 for YBCO-Ag composites. The improved resistance to thermal shock and subcritical crack growth is believed to be due to improvements in mechanical properties (strength and fracture toughness) and thermal conductivity of YBCO as a result of Ag addition.