INTERNAL FRICTION STUDY OF ANNEALING PROCESSES IN PILE-IRRADIATED GRAPHITE

A reactor grade graphite irradiated by fast neutrons at 30°C to the total dose of 5.8 × 1020 nvt was stepwise annealed between 100° and 2300°C, and was examined each time by measuring the internal friction and dynamic modulus at temperatures from 300° down to 80°K. The recovery process has been found to consist of three stages; the first stage occurring between 100° and 500°C, the second one in the range from 600° to 1150°C, and the third one between 1200° and 2300°C. In the first stage the dynamic modulus recovers for the most part, while the internal friction indicates little change. On the other hand, the recovery of internal friction arises mostly in the third stage where the dynamic modulus shows only a slight fall-off. In the second stage no serious change arises in the anelastic properties. A qualitative explanation for the formation and decomposition processes of interstitial clusters is given within the framework of the Granato-Lücke theory in relation to the behavior of such anelastic properties. © 1969.