Influence of strain conditions on the grain sub-structuration in crept uranium dioxide pellets

Saada, M. Ben; Iltis, X.; Gey, Nathalie; Beausir, Benoît; Miard, A.; Garcia, Philippe; Maloufi, Nabila

doi:10.1016/j.jnucmat.2019.02.052

Cited by 6 publications

(7 citation statements)

References 27 publications

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“…The grain size of each sintered batch was further determined from EBSD data, as described in [22]. The mean Equivalent Circular Diameters (ECD) 1 were 15 µm (± 1 µm) and 12 µm (± 1 µm), respectively, for B1-R and B2-R.…”

Section: Manufacturing Processmentioning

confidence: 99%

“…Sub-grain sizes were also quantified from EBSD maps. The procedure to evaluate the sub-grains proceeds in two steps considering an upper and lower threshold angle set here to 0.25° and 0°, respectively [22,25]. Finally, in order to explore sub-boundaries induced by creep and contrast their dislocation arrangements, Accurate-ECC images were acquired with a Zeiss Auriga 40 FEG-SEM equipped with a GEMINI-type electron column (with an accelerating voltage of 20 kV, a beam current of 550 pA and at a working distance of 7 mm) [26][27][28].…”

Section: Tests At Imposed Constant Stress (Creep Tests)mentioning

confidence: 99%

“…The deformed samples were characterized using an optimized protocol detailed in [21], for EBSD data acquisition and processing, to detect and quantify sub-boundaries with very low disorientation angles. This protocol was applied first on one batch of pellets and the corresponding results are presented in [22]. It allowed to quantify the evolution of sub-structure after deformation, in particular the linear fraction of sub-boundaries, from large EBSD maps, according to test conditions.…”

Section: Introductionmentioning

confidence: 99%

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Influence of intra-granular void distribution on the grain sub-structure of UO2 pellets after high temperature compression tests

Saada

Iltis

Gey

et al. 2021

Journal of Nuclear Materials

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The aim of this work is to study the role of the intra-granular voids, on the macroscopic behavior and the microstructure of uranium dioxide (UO 2 ) for different strain conditions in the dislocational creep regime. Two batches (B1 and B2) of stoichiometric UO 2 pellets were fabricated by adapted powder metallurgy processes to obtain very close mean grain size and porosity but different fractions of intra-granular voids: they were 2.5 times more numerous in the second batch. The pellets were then compressed at 1773 K mostly in the dislocational regime for different strain levels and strain rates. Large Electron BackScattered Diffraction (EBSD) maps were acquired to quantify the sub-boundaries fraction in each deformed sample (with reliable detection of disorientation lines down to 0.25°). Accurate-Electron Contrast Channeling Image (Accurate-ECCI) experiments were also performed to evidence the arrangement of dislocations in the sub-boundaries and highlight their interaction with intra-granular voids. The fractions of sub-boundaries and their disorientation increased in both batches with increasing strain levels and strain rates. This confirms that during creep, UO 2 is subject to a dynamic recovery mechanism. Interestingly, for similar deformation conditions, the pellets from batch B2 crept slower than those from batch B1. They also had a higher fraction of sub-boundaries which were more tortuous and located essentially close to the grain boundaries where the voids clustered. This suggests an influence of intra-granular voids on the creep rate, probably due to a void pinning effect of dislocation subboundaries. This effect should be taken into account to optimize the microstructure and mechanical properties of UO 2 nuclear fuel, in order to improve its behavior under irradiation.

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Section: Manufacturing Processmentioning

confidence: 99%

Section: Tests At Imposed Constant Stress (Creep Tests)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of intra-granular void distribution on the grain sub-structure of UO2 pellets after high temperature compression tests

Saada

Iltis

Gey

et al. 2021

Journal of Nuclear Materials

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“…This method allows fast and automatic/semi-automatic detection of grain boundaries but has only been used for the study of geological samples using optical microscopy. Furthermore, methods based on the recording of electron backscatter diffraction (EBSD) maps are under development [10,11,12]. The primary benefit of grain size measurement using EBSD over imaging of etched surfaces is that grain boundaries can be precisely identified owing to contrast modification due to the crystallographic orientation.…”

Section: Introductionmentioning

confidence: 99%

SEraMic: A semi-automatic method for the segmentation of grain boundaries

Podor

Goff

Lautru

et al. 2021

Journal of the European Ceramic Society

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The SEraMic method, implemented in the SEraMic plugin for Fiji or ImageJ software, was developed to calculate a segmented image of a ceramic cross section that shows the grain boundaries. This method was used to accurately and automatically determine grain boundary positions and further assess the grain size distribution of monophasic ceramics, metals, and alloys. The only required sample preparation is polishing the cross section to a mirror-like finish. The SEraMic method is based on at least six backscattered electron scanning electron microscopy images of a unique region of interest with various tilt angles ranging from -5° to +5°, which emphasises the orientation contrasts of the grains.Because the orientation contrast varies with the incident beam angle on the sample, the set of images contains information related to all the grain boundaries. The SEraMic plugin automatically calculates and builds a segmented image of the grain boundaries from the set of tilted images. The SEraMic method was compared with classical thermal etching methods, and it was applied to determine the grain boundaries in various types of materials (oxides, phosphates, carbides, and alloys). The method remains easy to use and accurate when the average grain diameter is greater than or equal to 0.25 µm.

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“…Generally, mechanical testing is preceded and/or followed by microstructural investigations in order to get the structure-property-processing relationships [4,5,6,7]. In situ characterization provides more useful data for a more realistic theoretical modeling, which allows for predicting the mechanical performance of components.…”

Section: Introductionmentioning

confidence: 99%

In Situ Macroscopic Tensile Testing in SEM and Electron Channeling Contrast Imaging: Pencil Glide Evidenced in a Bulk β-Ti21S Polycrystal

et al. 2019

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In this paper, we report the successful combination of macroscopic uniaxial tensile testing of bulk specimen combined with In situ dislocation-scale observations of the evolution of deformation microstructures during loading at several stress states. The dislocation-scale observations were performed by Accurate Electron Channeling Contrast Imaging in order to follow the defects evolution and their interactions with grain boundaries for several regions of interest during macroscopic loading. With this novel in situ procedure, the slip systems governing the deformation in polycrystalline bulk β-Ti21S are tracked during the macroscopic uniaxial tensile test. For instance, curved slip lines that are associated with “pencil glide” phenomenon and tangled dislocation networks are evidenced.

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Influence of strain conditions on the grain sub-structuration in crept uranium dioxide pellets

Cited by 6 publications

References 27 publications

Influence of intra-granular void distribution on the grain sub-structure of UO2 pellets after high temperature compression tests

Influence of intra-granular void distribution on the grain sub-structure of UO2 pellets after high temperature compression tests

SEraMic: A semi-automatic method for the segmentation of grain boundaries

In Situ Macroscopic Tensile Testing in SEM and Electron Channeling Contrast Imaging: Pencil Glide Evidenced in a Bulk β-Ti21S Polycrystal

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