Homogeneous nuclei and preexisting defects in materials are competitive for absorbing He atoms. These two ways are competing during actual nucleation process in materials suffering He ion irradiation.Īt low temperatures, thermal dissociation of He atoms from their traps is negligible. Homogeneous nucleation means that bubbles nucleate in perfect lattice position, while heterogeneous nucleation preferentially occurs on defects of materials, such as dislocations and interfaces. There are two types of nucleation of bubbles: homogeneous and heterogeneous nucleation. Consequently, bubble and void are two distinct forms of cavities, but with a strong connection. Then with the increasing of irradiated dose or temperature, bubbles would achieve a critical radius via absorbing more He atoms and vacancies and transform into voids. For cavity formation, first He atoms and vacancies agglomerate into clusters, which accelerate the bubble nucleation and growth. However, a void with plenty of vacancies has internal pressure much lower than equilibrium-pressure, so that the void has a faceted structure composed of close-packed planes. Usually, bubble is a kind of spherical cavity, possessing a high concentration of He atoms, hence the bubble has over-pressure or equilibrium-pressure. įor high dose irradiation, He atoms would accumulate to form defect clusters, such as interstitial clusters, He-vacancy clusters, cavities (bubbles and voids), which display different diffusion mechanisms: when T 0.5T m, the “vacancy mechanism” would be dominant, because He diffusion can be assisted by numerous vacancies (formed by thermal activation) that can move easily.īefore introducing the bubble nucleation, it is necessary to distinguish the forms of cavities, i.e., bubble and void. In the case of a low radiation dose, the concentration of defects introduced by irradiation is negligible low, hence He atoms diffuse effectively as interstitials at T 0.5T m, abundant vacancies would form by thermal excitation, hence He atoms could jump from one to the other vacancy. Since the activation energy of the He atoms interstitial migration is only a few tenths of eV, the He atoms can diffuse quickly at room temperature until they are trapped by other defects. (1) Interstitial migration: He atoms at interstitial sites diffuse interstitially. Schematic illustration of defect configurations and jump processes relevant for He diffusion without and with irradiation. Finally, we discuss the evolutions of properties of irradiated nanostructured materials. Then, we summarize the irradiation response in nanostructured materials, including the interactions between cavities and interfaces, and interface effects on irradiation damage. In this review, we first introduce He ion irradiation damage in materials. To understand the interface mechanisms and provide a theoretical basis for designing nuclear materials, we summarize these research achievements in this review. Recently, many achievements have been made to explore the interface mechanisms for designing suitable nuclear materials. However, the underlying mechanisms for interfaces enhanced irradiation resistance had not been revealed in-depth in the past. Prior studies show that nanostructured materials possess outstanding irradiation resistance because abundant interfaces can hinder the formation of cavities. He can combine with cavities and accelerate irradiation-induced swelling, hardening, embrittlement and surface deterioration. He is insoluble in most nuclear materials and its diffusion activation energy is low, so it is easy to form interstitials and He bubbles. In nuclear fission and fusion reactors, helium (He) ions are produced by the decay of tritium and the (n, α) reaction during neutron irradiation. The next generation nuclear reactors have increasing demands for the discovery of advanced materials that can survive severe radiation environments, so that nuclear reactors can operate safely for a prolonged period of time. As a reliable, sustainable and affordable energy, nuclear power provides more than 13% of electricity worldwide.
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