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

Abstract

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.

Ion irradiation-induced swelling and hardening effect of Hastelloy N alloy

“…The lattice expansion suggests that the defects are randomly distributed and their concentration is sufficient to influence the long range order, and M. Liu et al [11] have investigated the irradiation induced microstructural evolution of Hastelloy N alloy, they found that radiation induced defects in Hastelloy N alloy are mainly small vacancy and interstitial clusters at irradiation dose below 1 dpa, resulting in the beginning of microstrain just like the present study. When irradiation dose exceeds 1 dpa, the defects grew up by absorbing the point defects, and finally evolved into the dislocation loops.…”

“…In recent years, the high dose, high flux ion irradiations have been considered as a useful tool to understand the basic mechanisms of irradiation damage in structural materials, especially for the evolution of the irradiation induced microstructures and properties [5][6][7][8][9][10]. M. Liu et al investigated the microstructural evolution of Hastelloy N alloy using Ar ion irradiation and observed that the black dot defects and small dislocation loops emerged at dose of 0.4 and 4 dpa respectively, and the size of those loops increased with irradiation fluence [11]. K. Liu et al reported that the size and the density of defects produced at a low irradiation dose rate were larger and higher than that at a high irradiation dose rate [12].…”