| 1. |
- Eriksson, Johan, 1987, et al.
(författare)
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Solute Concentrations in the Matrix of Zirconium Alloys Studied by Atom Probe Tomography
- 2023
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Ingår i: ASTM Special Technical Publication. - 0066-0558. ; STP1645, s. 149-172
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Konferensbidrag (refereegranskat)abstract
- This work indicates that the matrix content of the alloying elements iron, chromium, and nickel in as-produced commercial Zircaloy-2-type materials is lower than what has been indicated by many previous studies. Atom probe tomography in voltage pulse mode was used to study the matrix content of solutes in Zircaloy-2 of type LK3/L and a similar model alloy, called Alloy 2, of the same heat treatment. Both alloys were analyzed in the as-produced state and after reactor exposure. In the as-produced materials, the concentrations of iron, chromium, and nickel were all below the detection limits of around 10 wt. ppm. After reactor exposure, these alloying elements were observed to reside in clusters at loops, and the matrix content (including clusters) of iron had increased to about 1,200 wt. ppm in the fueled region of the rod and to about half that value in the plenum region. The chromium content in the fueled region was approximately 100 wt. ppm, and the nickel content was approximately 200 wt. ppm. In the plenum region, the content of these elements was lower. However, due to an uneven distribution of clusters, there was a wide scatter in the measured concentrations in the irradiated materials. Additionally, the matrix concentrations of solute elements in (nonirradiated) Zircaloy-2 were investigated for a series of samples subjected to a annealing at 770◦C followed by cooling at different rates. From these measurements, the solubilities at 770◦C were estimated to be around 65 wt. ppm for chromium, at least 37 wt. ppm for iron, and below 9 wt. ppm for nickel. Slow cooling resulted in virtually no iron, chromium, or nickel in the matrix. The concentration of aluminum in the matrix was observed to be between 10 and 20 wt. ppm for all a-annealed samples and for the as-produced materials of commercial heat treatment.
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| 2. |
- Fabritius-Vilpoux, Kathia, et al.
(författare)
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Ultrastructural changes of bovine tooth surfaces under erosion in presence of biomimetic
- 2021
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Ingår i: Bioinspired, Biomimetic and Nanobiomaterials. - : Thomas Telford Ltd.. - 2045-9866 .- 2045-9858. ; 10:4, s. 132-145
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Tidskriftsartikel (refereegranskat)abstract
- Enamel and dentin are susceptible to acids from food sources leading to dental erosion, a global problem affecting millions of individuals. Particulate hydroxyapatite (HAP) on the tooth surface can influence the effects of acid attacks. Standardized bovine enamel and dentin samples with artificial saliva are used in an in vitro cyclic demineralization-remineralization protocol to analyze the structural changes experienced by tooth surfaces using high-resolution scanning electron microscopy and to evaluate the potential of a HAP-based oral care gel in the protection of teeth from erosive attacks. The interfaces between HAP particle and enamel HAP crystallites are investigated using focused ion beam preparation and transmission electron microscopy. The results show that erosion with phosphoric acid severely affects enamel crystallites and dentin tubules, while artificial saliva leads to remineralization effects. The HAP-gel forms a microscopic layer on both enamel and dentin surfaces. Upon acid exposure, this layer is sacrificed before the native tooth tissues are affected, leading to significantly lower degrees of demineralization compared to the controls. This demonstrates that the use of particulate HAP as a biomaterial in oral care formulations can help protect enamel and dentin surfaces from erosive attacks during meals using a simple and effective protection principle.
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| 3. |
- Kiranbabu, Srikakulapu, et al.
(författare)
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Influence of MnS inclusion characteristics on generation of white etching cracks in 100Cr6 bearing steel
- 2023
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Ingår i: Wear. - 0043-1648. ; 534-535
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Tidskriftsartikel (refereegranskat)abstract
- Wind turbine gearbox (WTGB) bearings suffer from premature failures through white etching cracks (WECs). To investigate causes of this failure mechanism, we tested two types of 100Cr6 bearing steel components. We carried out rolling contact fatigue experiments on standard washers and material extracted from a WTGB bearing. These differed strongly in morphology and orientation of non-metallic inclusions (NMIs) with respect to the raceway, especially of MnS-type. While the standard washer did not exhibit WECs formation, the WTGB bearing did - even under moderate conditions (1.9 GPa Hertzian pressure, 107 cycles). We therefore conclude that MnS-inclusions are a key factor in initiation of WECs in WTGB bearings.
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| 4. |
- Mayweg, David, 1986, et al.
(författare)
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Focused Ion Beam induced hydride formation does not affect Fe, Ni, Cr-clusters in irradiated Zircaloy-2
- 2023
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Ingår i: Journal of Nuclear Materials. - 0022-3115. ; 581
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature focused ion beam (FIB) milling is known to potentially promote the formation of hydrides in zirconium and its alloys. We used atom probe tomography (APT) to determine the composition of irradiated and as-produced Zircaloy-2 fuel cladding. We consistently found ∼ 50 at% hydrogen in all room temperature FIB-milled specimens run in voltage pulsing APT measurements. Crystallographic analysis of APT data however showed slightly better agreement with δ-hydride (ZrH2, FCC, ∼ 60–66.7 at% H) than γ-hydride (ZrH, FCT, ∼ 50 at% H). Electron energy loos spectroscopy (EELS) measurements prior to APT analyses confirmed the presence of δ-hydride. Hence, APT gives a systematic underestimation of hydrogen for Zr-hydride. Milling at cryogenic temperatures was found to not cause such hydride formation. However, we did not find significant differences in the clusters formed by segregation of the alloying elements Fe, Cr and Ni to irradiation induced a-loops whether the material was identified as α-Zr or hydride. Therefore, analyzing irradiation-induced redistribution of alloying elements in Zr fuel cladding using APT does not rely on FIB preparation at cryogenic temperatures. However, in conjunction with voltage pulsing APT cryo-FIB can be worthwhile if one aims at investigating hydrogen distribution or hydrides.
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| 5. |
- Mayweg, David, 1986, et al.
(författare)
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Formation of pure zirconium islands inside c-component loops in high-burnup fuel cladding
- 2024
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Ingår i: Journal of Nuclear Materials. - 0022-3115. ; 597
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Tidskriftsartikel (refereegranskat)abstract
- High-burnup Zr-based nuclear fuel claddings exhibit accelerated irradiation growth, corrosion and hydrogen pick-up, all correlated with the emergence of c-component dislocation loops. We made use of sub-nm-resolution atom probe tomography to characterize the nanoscale chemistry of c-loops in fuel cladding from boiling water reactor operation. We found segregation of Fe, Ni and Sn to dislocation lines and depletion of Sn and O inside the loops, resulting in nearly pure Zr islands. We also observed nucleation of suboxide inside one c-loop, pointing to a possible mechanism of accelerated in-reactor corrosion. Such Zr-islands might also promote hydride precipitation and associated degradation.
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