Use of Ion Bombardment to Study Irradiation Damage in Zirconium Alloys

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Abstract
Zircaloy-2 having several different microstructures, textures, and compositions has been bombarded with either 5 MeV or 46.5 MeV nickel ions at 300 to 600°C to achieve doses ranging from 0.65 to 87.0 displacements per atom (dpa). Similar material was reactor-irradiated near 320°C to neutron fluences between 0.8 and 3.2dpa. Transmission electron microscopy methods were used to identify and compare the nature of the defect structure produced by the ions and neutrons. For doses below 10 dpa (8 × 1021 neutrons (n)/cm2 (E> 1 MeV)) and temperatures below 400°C, the predominant defects formed by nickel ion bombardment are black spots and loops on the order of 100 Å (10 nm) diameter. For these conditions the damage appears to be similar in most ways to that produced by neutron irradiation. An exception is that a diffraction contrast effect termed “corduroy” is consistently observed after neutron irradiation but generally not after ion bombardment. At temperatures above 400°C, the residual microstructure appears to depend on the rate of displacement damage. For doses above about 10 dpa and irradiation temperatures between 400 to 500°C, bombardment with 5 MeV nickel ions produces a striking alignment of defects on {0002} planes. At 600°C, no residual irradiation damage was observed. For all conditions where damage was present, some of the defects had Burgers vectors with a component parallel to the C-axis. Possible implications of the various observations are discussed.