Investigation of defect ordering in heavily irradiated metals by high- voltage electron microscopy

Abstract

The development of radiation-induced contrast in Ag and Cu during heavy electron irradiation in a high-voltage electron microscope is investigated in the temperature range 20 to 394 K with particular attention to ordering phenomena. After fluences Φ of 1 MeV electrons of the order of magnitude 1026 to 1027 e− m−2 the following three regimes of irradiation temperatures Tirr can be distinguished in Cu. Tirr ⪅ 170 K (A): no ordering of visible defects (stacking-fault tetrahedra, dislocation loops) are observed. 170 K ⪅ Tirr ⪅ 350 K (B): ordering of stacking-fault tetrahedra in 〈100〉 directions, leading to simple cubic lattices at lower and to {100} walls at higher temperature. Tirr > 350 K (C): no visible radiation-induced contrast. In Ag the temperatures seperating the three regimes from each other are shifted towards lower temperatures by 20 K. In both metals the transition B/C is correlated with recovery stage III; there appears to be no correlation with recovery stage I, however. The observations are discussed in terms of self-organization associated with highly dissipative processes.