Microstructural Changes in Neutron-Irradiated Commercial Alloys: A Sequel

The effect of reactor irradiation on the microstructural stabilities of several high-nickel-content superalloys was evaluated by transmission electron microscopy. The alloys include Nimonic PE16 and the Inconel alloys 706 and 718. Specimens were irradiated in sealed, unstressed, sodium-filled capsules in the EBR-2. Irradiation temperatures ranged from 399 to 649/sup 0/C (750 to 1200/sup 0/F); specimens accumulated a peak fluence of 6 x 10/sup 22/ n/cm/sup 2/, E > 0.1 MeV. While little or no microstructural changes were observed in Nimonic PE16, the Inconels exhibited overaging precipitation effects - in particular, the formation of the stable overaging precipitate, eta - which increased with temperature in the range studied. Inconel 706 exhibited the more pronounced overaging effects, i.e., larger and coarser eta plates, consistent with its higher Ti/Al ratio. In general, the precipitation features noted in all three alloys were similar to those observed in identical material after ion bombardment with high energy nickel. The ion bombardment work has thus correctly predicted the microstructural response of these alloys to fast neutron irradiation.