Ductile to brittle transition behavior of Zr-2.5Nb pressure tubes

Fracture toughness tests were carried out at temperatures ranging from RT to 300 .deg. C on compact tension specimens of the Zr-2.5Nb containing up to 200 ppm H. Hydrides drastically decreased fracture toughness resistance, dJ/da of the Zr-2.5Nb pressure tube at RT along with the formation of fissures. However at higher temperatures larger than 200 .deg. C, little decrease in fracture toughness of the Zr-2.5Nb tube showed up along with no formation of the fissures. Thus, a ductile-brittle transition temperature lay in the temperature range of 130-180 .deg. C. Fissures are suggested to occur by fracture of hydrides by deformation twins accompanied during a crack growth in the Zr-2.5Nb tubes. The amount of deformation twins was determined though textural changes before and after tensile tests where the tensile stress was applied in the circumferential direction of the tubes. The ductile-to-brittle transition behavior of the Zr-2.5Nb tube with hydrogen concentration and heat treatment conditions is discussed in association with interaction of deformation twins and the γ- to δ-hydride phase transition, which causes the maximum fracture toughness of the as-received Zr-2.5Nb tube at 180 .deg. C