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Abstract
Hydrogen can be induced in various ways into reduced-activation ferritic/martensitic (RAFM) steels when they are used as structural materials for advanced nuclear systems. However, because of the fast diffusion of hydrogen in metals, the effect of hydrogen on the evolution of irradiation-induced defects was almost neglected. In the present work, the effect of hydrogen on the evolution of dislocation loops was investigated using a transmission electron microscope. Specimens of reduced-activation ferritic/martensitic (RAFM) steels were irradiated with hydrogen ions to 5 × 1020 H+ • m−2 at 523–823 K, and to 1 × 1020 H+ • m−2 − 5 × 1020 H+ • m−2 at 723 K. The experimental results reveal that there is an optimum temperature for dislocation loop growth, which is ~723 K, and it is greater than the reported values for neutron irradiations. Surprisingly, the sizes of the loops produced by hydrogen ions, namely, 93 nm and 286 nm for the mean and maximum value, respectively, at the peak dose of 0.16 dpa under 723 K, are much larger than that produced by neutrons and heavy ions at the same damage level and temperature. The results indicate that hydrogen could enhance the growth of loops. Moreover, 47.3% a0 <111> and 52.7% a0 <100> loops were observed at 523 K, but a0 <111> loops disappeared and only a0 <100> loops existed above 623 K. Compared with the neutron and ion irradiations, the presence of hydrogen promoted the formation of a0 <100> loops.
Highlights
A challenge for developing advanced nuclear systems, such as fusion reactors, GenerationIV fission reactors, and accelerator-driven spallation (ADS) devices, is the deep understanding of the complicated irradiation damage mechanisms in irradiation resistant materials [1,2,3,4].Reduced-activation ferritic/martensitic (RAFM) steels are considered as prime candidate structural materials for advanced nuclear systems, owing to their excellent mechanical properties, microstructural stability, and irradiation resistance [5,6,7]
Previous studies have investigated evolution of loops in body-centered andiron iron–chrome alloys with irradiations of neutron and heavy ion, which is summarized cubiciron and iron–chrome alloys with irradiations of neutron and heavy ion, which in is Compared to neutron and heavy ion, we find that hydrogen ion irradiations produce summarized in Table 2 [23,24,25,26,27,28,29,30,31,32,33]
The evolutions of the dislocation loops that are dependent on irradiation temperature and fluence were investigated using transmission electron microscope (TEM) observations in RAFM steel irradiated by hydrogen ions
Summary
Reduced-activation ferritic/martensitic (RAFM) steels are considered as prime candidate structural materials for advanced nuclear systems, owing to their excellent mechanical properties, microstructural stability, and irradiation resistance [5,6,7]. The properties of the RAFM steels will degrade when they are exposed to conditions of high energy neutron irradiations, such as 14 MeV for fusion reactors and hundreds of MeV for ADS devices. In such conditions, hydrogen and helium are Materials 2018, 11, 2276; doi:10.3390/ma11112276 www.mdpi.com/journal/materials. Because the diffusion of hydrogen is fast, it was generally understood that hydrogen would diffuse out of steels, and that it had little effect on microstructure evolution, especially at elevated temperatures [4]
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