Fracture toughness of zirconium hydride and its influence on the crack resistance of zirconium alloys

Measurements of fracture toughness have been made on specimens of delta-zirconium hydride and two-phase mixtures of hydride and zirconium. The tests were carried out over the temperature range of 20 to 3000C on both hydrided zirconium and hydrided Zr-2.5%Nb. The results are discussed in terms of the threshold stress intensity for hydrogen-induced subcritical crack growth in Zr-2.5%Nb. The effect of hydride on the fracture toughness of zirconium alloys at 20 and 3000C is also discussed. We conclude that the improvement in toughness of hydride-containing zirconium alloys above 1500C is primarily due to the improved ductility of the zirconium phase rather than to improvements in the hydride properties. (orig.)