Abstract
The behaviour of the ordered alloy Zr3Al has been iavestigated by transmission electron microscopy following ion bombardments at temperatures ranging from 30 to 850 K. The diffraction-contrast features of individual damaged regions produced by low-fluence C+, N+ or Ar+ ions (0·5–2·0 MeV) were examined. Imaging with fundamental reflections revealed strain-contrast images arising from defect clusters which have essentially a spherically symmetrical strain-field and which presumably also encompass disordered regions. Other disordered regions, which were not associated with the defect clusters, were rendered visible due to structure factor contrast by imaging with 110 superlattice reflections. Both types of damaged regions were observed to anneal out in the region 723–848 K.
With increasing bombarding ion fluence, Zr3Al gradually disordered and this transition was monitored by assessing the change in the long-range order parameter S. Post-irradiation annealing and high-temperature irradiation experiments revealed that reordering of the disordered alloy also occurred in the region 723–848 K, probably due to the diffusion of vacancies. Zr3Al could also be eventually rendered amorphous by bombarding at fairly high ion fluences. The fluence required to reach a particular disordered state and degree of amorphicity was dependent upon the amount of annealing that occurred within the defect cascade during the bombardment.