Abstract
In the present work, an ODS 12 Cr steel was characterized using Electron Microscopy techniques, in an as-received condition and after annealing treatments between 773 K and 1573 K. Results show a complex microstructure, with the presence of fine Y–Ti–O nanoparticles dispersed in the matrix. After annealing at 1573 K, the average diameter of Y–Ti–O nanoparticles increases from ~ 4 to ~ 7 nm and partial recrystallization occurs. The trapping behavior of deuterium in the steel in its as-received state and annealed at 1573 K was investigated. Samples were exposed to low-energy deuterium plasma and analyzed with thermal desorption spectroscopy, after waiting times of 1 day and 25 days. The samples measured 1 day after exposure released a higher total amount of deuterium than the ones measured after 25 days. The effect of waiting time is explained by the release of deuterium, at 300 K, from sites with low activation energy for detrapping, Ed. In the as-received condition, part of the deuterium detrapped at 300 K was re-trapped by high-Ed sites. For the samples in the annealed condition, the redistribution of deuterium from low-Ed to high-Ed sites was not observed, but the total amount of deuterium released was higher.
Highlights
ODS ferritic steels have been extensively studied in the past decades due to their potential application as fuel cladding tubes in nuclear fast breeder reactors and on fusion reactor blankets
The microstructural characterization of the ODS 12 Cr steel after 1 hour annealing treatments at different temperatures allow the following conclusions: (i) The microstructure of the ODS 12 Cr steel is complex, formed by a variety of highly thermally stable components: a ferritic matrix composed of nanosized and micrometric grains, which has an intrinsic resistance to recrystallization due to its texture; incoherent TiC particles, even present after annealing at 1573 K for 1 hour and pores containing coarse Y–Ti–O-based particles, likely formed due to Ar retention during mechanical alloying and Y–Ti–O nanoparticles
It was possible to detect with Transmission Electron Microscope (TEM) an increase in average diameter of Y–Ti–O nanoparticles from ~ 4 to ~ 7 nm, which was associated to partial recrystallization of the material and to the decrease in hardness
Summary
ODS ferritic steels have been extensively studied in the past decades due to their potential application as fuel cladding tubes in nuclear fast breeder reactors and on fusion reactor blankets. Depending on morphological characteristics of these trapping sites and their distribution throughout the metallic matrix, they can become stress raisers when bound to these elements, leading to embrittlement and fracture during service, or they can be beneficial for increasing the resistance to damage.[21] Since it is not possible to prevent the formation of radiation-induced defects and the generation of He, H, D, and T in the metallic structure, the engineering of trapping sites becomes the most suitable approach to improve the resistance to this type of damage and that is how oxide nanoparticles in ODS steels can play their role These particles can retain the diffusible elements and make them inactive in the material, preventing their recombination or agglomeration at detrimental sites, like grain boundaries (leading to intergranular fracture), regions with microstructural banding, and elongated inclusions. Samples of ODS 12 Cr steel in the as-received condition and annealed at 1573 K for 1 hour were exposed to low-energy D2 plasma and analyzed with Thermal Desorption Spectroscopy, in order to study the trapping behavior of D and its interaction with Y–Ti–O nanoparticles
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