Degradation of the mechanical properties of Zircaloy-4 due to hydrogen embrittlement

During nuclear reactor operation, the embrittlement of components made of zirconium-based alloys is observed. The degradation of their mechanical properties is due to the combined effect of hydrogen absorption and the damage caused by neutron irradiation. In this work we studied the influence of hydrogen content on the fracture toughness of a Zircaloy-4 alloy, Compact tension (CT) specimens were obtained from a hot-rolled, annealed and finally cold-rolled material. The observed microstructure consisted of alpha-Zr rounded grains with diameters of about 15 mum. Selection of the tested material was guided by the need to perform experiments on samples with a texture equivalent to the cladding components of Candu-type nuclear reactors. The specimens were fatigue precracked and hydrogen charged before testing. Two different reactions were performed. Specimens with a final hydrogen content ranging from 10 to 400 ppm were obtained by electrochemical charging and those with a final concentration of up to 2000 ppm were charged by absorption under a gaseous atmosphere. In both cases, an homogeneous distribution of dissolved hydrogen and hydride phases was obtained. The dependence of the toughness on temperature and hydrogen content was measured on CT specimens. The analysis was performed in terms of J-integral and resistance curves. (C) 2002 Elsevier Science B.V. All rights reserved.