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The roles of stress state and crystallographic texture on plastic flow fracture and fracture behavior were examined for Zircaloy-2 sheet specimens irradiated to fluences of 0.7 to 1.9 × 1021 neutrons/cm2 (E > 1 MeV) at 327°C. The extent of strengthening achieved by texture was determined by comparing the level of flow strength obtained under the plane strain loading condition to that of simple uniaxial tension, all at the test temperature of 250°C. It was demonstrated that the relative aspects of texture strengthening were retained in the post-irradiation tests; that is, the material with the peak basal pole density parallel to the sheet normal evidenced less ductility than that with the peak basal pole density inclined at 30 deg to the sheet normal. Supporting evidence is presented in terms of the changes in flow stress and ductility with texture and by the magnitude of R, the ratio of the transverse plastic strains. Plane strain loading increased the flow stress by 66 percent in the material having the peak basal pole density parallel to the sheet normal, but did not change the flow stress for material with the peak pole density inclined > 60 deg to the sheet normal. Texture strengthening persisted to the maximum fluence tested, suggesting a strong texture effect on the mechanical behavior of irradiated materials. The overall level of strain at fracture was substantially reduced by irradiation. The deformation and fracture modes were also strongly affected by texture as well as by the loading methods. The irradiated Zircaloy sheet with the peak basal pole density in the normal direction tended to deform by means of sharply defined deformation bands; intersection of these bands also leads to initiation of fracture. In the other materials (peak basal pole densities inclined to the normal by angles > 30 deg) the deformation bands tended to be more diffuse.
zirconium alloys, fractures (materials), texture, irradiation, strains, stresses, mechanical properties
Technical specialist, Vallecitos Nuclear Center, General Electric Co., Pleasanton, Calif.
Metallurgist, Research and Development Center, General Electric Co., Schenectady, N. Y.