TEM investigation on the microstructural evolution of hastelloy N induced by Ar+ ion irradiation

Hastelloy N alloy has been selected as the primary structure material for molten salt reactor. In this article, Hastelloy N alloy samples were irradiated to different doses at room temperature using 300 keV Ar⁺ ions. The microstructural evolution was investigated by transmission electron microscopy (TEM) and energy‐dispersive spectroscopy (EDS). Black dot defects emerged in sample irradiated at low dose (0.4 displacement per atom (dpa)), and they grew up with irradiation doses (0.4–2 dpa). A high density of small dislocation loops (nano meters in size) were observed in the sample irradiated to 4 dpa. When the ion dose increased to 12 dpa, complicated structures with defects (including dislocation lines, larger loops and smaller black dots) were observed. Dislocation networks were detected from high‐angle annular dark field (HAADF) images. Larger dislocation loops (size: 30–80 nm) were visible in the sample irradiated to 40 dpa. Irradiation with dose of 120 dpa led to the formation of face‐centered cubic nanocrystallites with preferred orientations. Microsc. Res. Tech. 77:161–169, 2014. © 2013 Wiley Periodicals, Inc.