Metallographic studies of fatigue in 20% cold-worked zircaloy-2 containing zirconium hydride

The fatigue behaviour of unhydrided and hydrided 20% cold-worked zircaloy-2 reactor pressure-vessel tubing has been studied for fluctuating tension at room-temperature and 300 °C and for reversed torsion at room-temperature. At room-temperature, high concentrations of zirconium hydride markedly reduce the critical crack length. This effect is attributed to a lowering of the fracture toughness, since hydrides fracture in the path of crack propagation and promote matrix cleavage. At 300 °C, hydride particles constrained by the matrix are plastically deformed without fracturing; the toughness is probably unaffected by the presence of hydride.