Collision cascades in Zr 2Fe, Zr 3Fe and ZrFe 2

Abstract

In the present investigation, 15–350 keV 209Bi ion irradiations and subsequent transmission-electron-microscope (TEM) investigations were performed to provide detailed information on collision cascades in Zr 2Fe, Zr 3Fe and ZrFe 2. Low fluence (10 11–10 12 ions cm −2) irradiations were performed at 35–40 K with the 209Bi ions in order to observe the nature of the damage produced in individual collision cascades, as well as in early stages of cascade overlap. At high values for the average deposited-energy density ▪ in the cascade, which corresponded to low-energy heavy-ion implants (e.g. 15–30 keV Bi in Zr 2Fe, Zr 3Fe and ZrFe 2), the visible damage produced in a cascade consisted mainly of a single damaged region. With decreasing values of ▪ (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 ( ▪ decreased), the fraction of the theoretical collision cascade volume that was occupied by the visible damaged regions within a cascade decreased rapidly. The crystalline-to-amorphous transformation in Zr 2Fe, Zr 3Fe and ZrFe 2 bombarded with heavy ions appears 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.