Swelling and irradiation induced microstructural changes in nickel-based alloys

Three nickel alloys, Inconel X750, Inconel 600, and Inconel 625, and a 20 percent cold-worked Type 316 stainless steel were bombarded with 5-MeV nickel ions at 6500C to damage levels up to 90 displacements per atom. Post bombardment examination was carried out using 1-MeV transmission electron microscopy to image the entire range of ion damage. The evolution of the microstructure as a function of depth and displacement damage was determined by stereo microscopy. Despite variations in base composition and initial microstructure the three nickel alloys behaved in a similar fashion and exhibited an order of magnitude less swelling than the Type 316 stainless steel. In Inconel X750 containing a dispersion of γ', loss of coherency of the γ' particles occurred at very low doses at 550, 600, and 6500C. At 600 and 6500C the irradiation induced loop structure was controlled by the initial distribution of γ', and further precipitation of fine γ' occurred in the rest of the matrix