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

Blisters were grown in Zr-7.5Nb pressure tube sections by a thermal gradien t without applying external stress. The surrounding hydride distribution wa s 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 formatio n. The misfit strain produced by hydride blister growth provides the stress necessary to promote radial precipitation. During the subsequent tensile t est at 200 degrees C (delayed hydride cracking test) the radial hydride len gth and thickness are increased. This increase is explained by a stress con centrator effect of the blister. When this effect vanishes, the increase of radial hydrides continues by an autocatalytic effect and stress concentrat or effect of the hydride platelet. If a crack originated in the blister rea ches the matrix it could propagate along a radial hydride previously precip itated. (C) 1999 Elsevier Science B.V. All rights reserved.