Atom probe microscopy characterization of as quenched Zr–0.8wt% Fe and Zr–0.15wt% Cr binary alloys

Gault, Baptiste; Felfer, Peter; Ivermark, Maria; Bergqvist, Hans; Cairney, Julie M.; Ringer, Simon P.

doi:10.1016/j.matlet.2012.09.059

Cited by 10 publications

(8 citation statements)

References 34 publications

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“…The datasets were reconstructed using state-of-the-art algorithms [63], resulting in the typical tomograms shown in Figure 1(a) for a binary Cr-Zr specimen containing 0.26 at % Cr. Therein, a 2 at% Cr isoconcentration surface highlights the presence of small regions enriched in Cr, up to 4-5 at%, which appear to be aligned, maybe along a twin boundary, similar to what was discussed in [49]. The signal to background noise ratio on the major peak of Cr was 120:1, and on the major peak of Fe it was above 200:1, providing a high level of certainty when labelling the Cr and Fe atoms.…”

Section: Atom Probe Tomographysupporting

confidence: 75%

“…The 125 g buttons were re-melted three times in order to ensure chemical homogeneity. Further details of the materials processing can be found in [49,50]. The buttons were analysed at Western Zirconium using induced coupled plasma-atomic emission spectroscopy and combustion analysis (oxygen and nitrogen) to determine the chemical constituent of each sample, presented in Table 1.…”

Section: Methodsmentioning

confidence: 99%

“…The latter are similar to split radial distribution functions investigating the local neighbourhood of each atom along a specific direction. Another common data treatment technique, the calculation and analysis of the distance between a given species and its first nearest neighbours [73][74][75], was also used here to estimate the matrix composition following the protocol described in [75] as reported in [49], but also to investigate the clustering tendency of Cr in Zr.…”

Section: Atom Probe Tomographymentioning

confidence: 99%

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From solid solution to cluster formation of Fe and Cr in α -Zr

Burr

Wenman

Gault

et al. 2015

Journal of Nuclear Materials

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To understand the mechanisms by which the re-solution of Fe and Cr additions increase the corrosion rate of irradiated Zr alloys, the solubility and clustering of Fe and Cr in model binary Zr alloys was investigated using a combination of experimental and modelling techniques -atom probe tomography (APT), x-ray diffraction (XRD), thermoelectric power (TEP) and density functional theory (DFT). Cr occupies both interstitial and substitutional sites in the α-Zr lattice; Fe favours interstitial sites, and a low-symmetry site that was not previously modelled is found to be the most favourable for Fe. Lattice expansion as a function of Fe and Cr content in the α-Zr matrix deviates from Vegard's law and is strongly anisotropic for Fe additions, expanding the c-axis while contracting the a-axis. Matrix content of solutes cannot be reliably estimated from lattice parameter measurements, instead a combination of TEP and APT was employed. Defect clusters form at higher solution concentrations, which induce a smaller lattice strain compared to the dilute defects. In the presence of a Zr vacancy, all two-atom clusters are more soluble than individual point defects and as many as four Fe or three Cr atoms could be accommodated in a single Zr vacancy. The Zr vacancy is critical for the increased apparent solubility of defect clusters; the implications for irradiation induced microstructure changes in Zr alloys are discussed. (P.A. Burr) SPP dissolution [1,3,[20][21][22][23][24][25][26]. It is important to limit hydrogen uptake during reactor operation because hydrogen causes dimensional changes to the cladding [24], reduces its ductility [24] and reduces integrity performance in hypothetical accident scenarios [27,28], and potentially in the storage conditions relevant to spent nuclear fuel [27,29].Recent advanced transmission electron microscopy (TEM) [30] and atom probe tomography (APT) studies [31] have shown that clusters of Fe and Cr form at a and c dislocation loops following the re-solution process. This was previously suggested by TEM investigation [9-11, 17, 18, 32, 33] but not observed directly. It has been suggested that irradiation induced defects may also act as trapping sites for hydrogen, thereby increasing the terminal solid solubility of hydrogen in α-Zr [34,35].The solubility of Fe in Zr -and to a lesser extent also that of Cr in Zr -has also been investigated using atomic scale simulations, but so far, the clustering behaviour of alloying elements has hardly been con-

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Section: Atom Probe Tomographysupporting

confidence: 75%

Section: Methodsmentioning

confidence: 99%

Section: Atom Probe Tomographymentioning

confidence: 99%

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From solid solution to cluster formation of Fe and Cr in α -Zr

Burr

Wenman

Gault

et al. 2015

Journal of Nuclear Materials

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“…The addition of iron has also been shown to reduce the HPUF in zirconium alloys [8], whereas other authors report the opposite effect through a different mechanism [9,10]. In the metal substrate, it is found that iron atoms are readily rejected from the matrix of zirconium alloys, forming secondary phase particles (SPPs) but also segregating to grain boundaries [11,12]. The sizes and compositions of SPPs have also been linked to HPUF [9,10,13,14].…”

Section: Introductionmentioning

confidence: 99%

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Than

Wenman

Bell

et al. 2018

Journal of Nuclear Materials

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Simulations based on density functional theory (DFT) were used to investigate the behaviour of substitutional iron in both tetragonal and monoclinic ZrO 2. Brouwer diagrams of predicted defect concentrations, as a function of oxygen partial pressure, suggest that iron behaves as a p-type dopant in monoclinic ZrO 2 while it binds strongly to oxygen vacancies in tetragonal ZrO 2. Analysis of defect relaxation volumes suggest that these results should hold true in thermally grown oxides on zirconium, which is under compressive stresses. X-ray absorption near edge structure (XANES) measurements, performed to determine the oxidation state of iron in Zircaloy-4 oxide samples, revealed that 3+ is the favourable oxidation state but with between a third and half of the iron, still in the metallic Fe 0 state. The DFT calculations on bulk zirconia agree with the preferred oxidation state of iron if it is a substitutional species but do not predict the presence of metallic iron in the oxide. The implications of these results with respect to the corrosion and hydrogen pickup of zirconium cladding are discussed.

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“…On the contrary, the absence of Nb along with the higher O content facilitates the formation of Widmanstätten structures in Zr702. It is also noted that both Fe and Cr have rather low solid solubilities (<150 wppm [36]) but relatively high diffusion coefficients in α-Zr [37,38]. This explains why the relatively low additions (~750 wppm) of Fe and Cr in the Zr702 material allow the precipitation of Fe/Cr-bearing particles during the β water cooling, as shown in Figure 3b.…”

Section: Discussionmentioning

confidence: 99%

Comparative Study of Microstructural Characteristics and Hardness of β-Quenched Zr702 and Zr–2.5Nb Alloys

et al. 2019

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In this study, two commercial Zr alloys (Zr702 and Zr–2.5Nb) were subjected to the same β-quenching treatment (water cooling after annealing at 1000 °C for 10 min). Their microstructural characteristics and hardness before and after the heat treatment were well characterized and compared by electron channel contrast (ECC) imaging, electron backscatter diffraction (EBSD) techniques, and microhardness measurements. Results show that after the β quenching, prior equiaxed grains in Zr702 are transformed into Widmanstätten plate structures (the average width ~0.8 μm) with many fine precipitates distributed along their boundaries, while the initial dual-phase (α + β) microstructure in Zr–2.5Nb is fully replaced by fine twinned martensitic plates (the average width ~0.31 μm). Differences in alloying elements (especially Nb) between Zr702 and Zr–2.5Nb are demonstrated to play a key role in determining their phase transformation behaviors during the β quenching. Analyses on crystallographic orientations show that the Burgers orientation relationship is well obeyed in both the alloys with misorientation angles between α plates essentially focused on ~60°. After β quenching, the hardnesses of both alloys were increased by ~35%–40%. Quantitative analyses using the Hall–Petch equation suggest that such an increase was mainly attributable to phase transformation-induced grain refinements. Since Nb is able to effectively refine the β-quenched structures, a higher hardness increment is produced in Zr–2.5Nb than in Zr702.

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Atom probe microscopy characterization of as quenched Zr–0.8wt% Fe and Zr–0.15wt% Cr binary alloys

Cited by 10 publications

References 34 publications

From solid solution to cluster formation of Fe and Cr in α -Zr

From solid solution to cluster formation of Fe and Cr in α -Zr

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Comparative Study of Microstructural Characteristics and Hardness of β-Quenched Zr702 and Zr–2.5Nb Alloys

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