Hydride distribution around a blister in Zr-2.5Nb pressure tubes

Blisters were grown in Zr-7.5Nb pressure tube sections by a thermal gradient without applying external stress. The surrounding hydride distribution was analyzed. Hydride platelets were observed in the radial direction of the blister. The precipitation of these hydrides was found to be favored by low temperature of blister growth and slow cooling rate after blister formation. The misfit strain produced by hydride blister growth provides the stress necessary to promote radial precipitation. During the subsequent tensile test at 200 degrees C (delayed hydride cracking test) the radial hydride length and thickness are increased. This increase is explained by a stress concentrator effect of the blister. When this effect vanishes, the increase of radial hydrides continues by an autocatalytic effect and stress concentrator effect of the hydride platelet. If a crack originated in the blister reaches the matrix it could propagate along a radial hydride previously precipitated. (C) 1999 Elsevier Science B.V. All rights reserved.