The production of ordered defect structures in metals by neutron and charged particle bombardment is reviewed. Specific examples of a cubic array of aligned defect clusters are shown in nickel bombarded with 5-MeV nickel ions to 15 displacements per atom (dpa). The effect appears to occur only at temperatures between 280 and 450 C (536 and 842 F). Random defect arrays were found after 40, 180, 525, and 500 C (104, 356, 977, and 932 F) irradiation.
Ordered arrays of voids are shown in Ni nickel-irradiated to 300 to 400 dpa at 525 C and in molybdenum, Mo-0.5Ti, titanium-zirconium molybdenum alloy (TZM), columbium, tungsten, and tantalum irradiated with both neutrons and heavy ions. The structure of the voids is consistent with the parent lattice, that is, face centered cubic (fcc) in nickel and body centered cubic (bcc) in the refractory metals. A summary of the information reported to date reveals that the ratio of the lattice parameter of the void superlattice divided by the void radius varies from 5 to 17. The general features of the ordered void lattice are discussed in view of current theories that depend on strain interactions between the voids, anisotropic interstitial atom fluxes, and an approach to steady state at high displacement values.