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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 Experimental Breeder Reactor II. Irradiation temperatures ranged from 399 to 649°C (750–1200°F); specimens accumulated a peak fluence of 6 × 1022 n/cm2, 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 titanium-to-aluminum 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 ions at comparable temperatures. (The latter work was presented in a similar symposium and published in ASTM STP 611). The ion bombardment work has thus correctly predicted the microstructural response of these alloys to fast neutron irradiation.
radiation, ion bombardment, simulation, radiation damage, overaging, precipitation hardening, transmission electron microscopy
Senior Engineer, Vallecitos Nuclear Center, General Electric Co., Pleasanton, Calif.
Senior Engineer, Advanced Reactor Systems Department General Electric Co., Sunnyvale, Calif