Fracture behaviour of As fabricated and hydrogen charged Zr-2.5 wt % Nb pressure tubes made from double and quadruple vacuum arc melted ingots

This article discusses the fracture behaviour of pressure tubes fabricated from quadruple vacuum arc remelted (QM) and double arc remelted (DM) Zr-2.5 wt % Nb ingots. The fracture behaviour of these alloys have been characterized using J-R curves over the temperature range of 27 to 300 deg C using single specimen test techniques and load normalization method. Effect of hydrogen ingress on the fracture properties have also been investigated. The acoustic emission (AE) activity was monitored during the tensile pull of precracked compact tension specimen to observe differences during the fracture process. Significant enhancement in the initiation and crack growth fracture toughness was found for quadruple melted alloys over the entire range of test temperature (ambient to 300 deg C). As fabricated pressure tubes when charged with different levels of hydrogen show sharp reduction in fracture toughness values at ambient temperature. The fracture toughness of hydrided material slowly increases with the increase in the test temperature and above 150 to 170 deg C a sharp increase in the toughness values are observed in the DM alloy. Hydrided QM alloy showed marginally better fracture properties than DM alloys, at low hydrogen levels (25 ppm), which is attributed to the inherently higher toughness of QM matrix. (author)