Abstract
The major objective of the present investigation was to apply the impression test method to determine the effects of thermal annealing and neutron irradiation on the anisotropic mechanical characteristics of Zircaloy TREX (tube-reduced extrusion) from which thin-walled cladding tubes are pilgered. The impression method gives a rather direct evaluation of the mechanical strengths along the three orthogonal directions of thick-walled tubings. The method was applied to study the effects of thermal annealing on Zircaloy-4 and neutron irradiation on Zircaloy-2 TREX. These results enabled an evaluation of the mechanical anisotropy parameters R and P, which are the contractile strain ratios along the axial and hoop directions. Crystallographic textures of the TREXs were characterized by constructing basal, prismatic, and pyramidal pole figures using an X-ray diffraction method from which crystallite orientation distribution functions were derived and used, in conjunction with plasticity models, to predict the anisotropy parameters. While reasonable correlations between model predictions and experimental results were noted in some cases, the presence of a texture gradient along the wall thickness of the TREX causes, in most cases, the texture-based model predictions to deviate from the experimental results. A limited number of Zircaloy-2 samples were neutron irradiated to a total fast ( > 1 MeV) fluence of approx 1.7 x 10 exp 18 n/cm exp 2 , and the effect of radiation on anisotropic mechanical properties was studied. The irradiation was observed to increase the mechanical strength and decrease the yield anisotropy of the material due to a strong effect of irradiation on the prismatic slip system, which is a major deformation mode in the unirradiated condition. This makes other deformation modes contribute, resulting in the observed decrease in yield anisotropy.