Helium solubility and bubble formation in a nanostructured ferritic alloy

摘要

The response of a nanostructured ferritic alloy to He implantation and post-irradiation annealing (PIA) at 750 ℃ was characterized by atom probe tomography and transmission electron microscopy. The supersaturated He concentration in the ferrite at a dose of ~2.1 displacements per atom was similar for the as-implanted, 75 ± 7 appm, and a 10 h PIA treatment, 71 ± 7 appm, but decreased to 38 ± 2 appm after a 100 h PIA treatment. Approximately 91-97% of the He bubbles were present as isolated bubbles in the ferrite and ~1-5% on the surface of the nanoclusters in the ferrite. The remainder were associated with the grain boundaries with a small fraction on the surface of Ti(N,C,O) precipitates. Their average size and number density were similar for the as-implanted and 10 h PIA treatment with a small increase in the size and a significant increase in the number density after the 100 h PIA treatment. Swelling in the high dose region increased from ~1% in the as-implanted and 10 h PIA conditions to ~5% after the 100 h PIA treatment but the estimated number of He atoms per unit volume in the He bubbles decreased by an order of magnitude. Number densities increased from ~8 ×10~(23) m~(-3) in the as-implanted to ~15 ×10~(23) m~(-3) in the 10 h PIA condition, with little change (to ~12 ×10~(23) m~(-3)) in the 100 h PIA condition. This trend may indicate nucleation of new bubbles up to 10 h, with growth and possible consumption of the smaller bubbles between 10 and 100 h.