Collision cascades in Zr 3Fe

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The objective of the present research is to understand better the processes that control irradiation-induced phase changes and solute segregation in zirconium alloys. Previously, it was found that 0.5–1.5 MeV 40Ar ion irradiations resulted in the conversion of the crystalline Zr 3Fe orthorhombic phase to the amorphous state. In the present investigation, 15–1500 keV 209Bi ion irradiations (10 11–10 14 ions cm −2) were performed to provide more detailed information on collision cascades in Zr 3Fe. Consecutive ion bombardments with 1.5, 1.0 and 0.5 MeV 209Bi ions showed that complete amorphization occurred from 35 K to at least 600 K. Low fluence (10 11–10 12 ions cm −2) irradiations performed at35–40 K with 15–350 keV 209Bi ions provided information in the nature of the damage produced within individual damage cascades. At high values for the average deposited-energy density θ ν in the cascade, which corresponded to low-energy heavy-ion implants (e.g. 15–30 keV Bi in Zr 3Fe), the visible damage produced in a cascade consisted of a single damaged region. With decreasing values of θ ν (i.e. increasing ion implant energies), there was an increasing tendency for multiple damaged regions (subcascades) to form within a main cascade. The visible damaged regions appeared to be amorphous. It was also found that as the Bi ion energy increased ( θ ν decreased), the fraction of the theoretical collision cascade volume that was occupied by the visible damaged regions within a cascade decreased rapidly. The crytalline-to-amorphous transformation appeared to be the result of direct amorphization within the collision cascades and a critical defect concentration being reached in the cascade overlap regions, thus producing additional amorphous regions.