Influence of fabrication history on stress-oriented hydrides in zircaloy tubing

Abstract

The stress orientation of hydride platelets and crystalline textures of seamless Zircaloy tubing were related to the fabrication history. Stress-induced changes in preferred hydride orientations were measured with applied tensile and compressive stresses in the three major tubing directions. Changes in preferred hydride orientations were determined from frequency distributions of individual hydride platelets as measured with specially designed equipment. The susceptibility to stress-orientation of the hydrides was very high for the hot-reduced tube; essentially 100% of the hydrides were reoriented at moderate stress levels. In contrast, the stress-orientation susceptibility was lower and very similar for all cold-reduced tubing, i.e., tubing fabricated by reducing the diameter at ambient temperature. Thus, susceptibility to stress-orientation of the hydrides appeared to be a characteristic of the type of reduction, i.e., hot-reduced or cold-reduced, and was not dependent on the amount of reduction in diameter or wall thickness during fabrication. On this basis, the susceptibility to stress orientation of hydride platelets that was observed for these cold-reduced tubes can be applied to a first approximation to other cold-reduced tubes. Hydride-orientation distributions and stress-orientation susceptibilities could not be related to Zircaloy texture. Habit planes for the hydrides are discussed.