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The onset of plastic instability in irradiated materials is known to be governed by deformation processes that occur on a microscopic scale. In order to identify the nature of the controlling mechanisms giving rise to plastic instability, details of the deformation processes were examined for Zircaloy-2 irradiated to fluences of 1.0 to 3.0 × 1021 neutrons (n)/cm2 (E >1 MeV) and tested in inert and 0.3-torr iodine atmospheres at 322 ∼ 335°C. For irradiated materials tested in air, it was shown that plastic strain at the maximum load decreased by more than an order of magnitude relative to unirradiated material, especially under plane-stress conditions. This was due largely to concentrated shear deformation resulting from dislocation channel development. When the similar materials were tested in iodine, the load-carrying capacity was reduced further. Based on the evidence obtained by metallographic examination, a model has been proposed describing deformation behavior of irradiated plane-stress specimens by assuming consecutive formation and strain hardening of new deformation zones containing channels. Crack nucleation under an iodine atmosphere is believed to occur when the local strain at the channel zone becomes sufficiently large to break oxide films and cause intergranular cracking.
zirconium, mechanical properties, irradiation, zirconium alloys, dislocation (materials), crack initiation, iodination, stress corrosion, plastic properties, deformation
Staff, Corporate Research and Development, General Electric Company, Schenectady, N.Y.
Manager, General Electric Company, Pleasanton, Calif